D04B - INSTALLATION GUIDE - INSTALLATION

D04B-1 Hardwood flooring installation - General requirements
D04B-2 Hardwood flooring installation methods
D04B-3 Installation requirements
D04B-4 Installation of hardwood flooring
D04B-5 Installation problems
D04B-6 Site finishing of hardwood flooring
Preface:
This study guide covers the installation requirements for solid and engineered strip, plank, and parquet hardwood flooring and related materials. Specifiers and/or persons using this guide should verify all facts relative to the particular project installation requirements.

1 • HARDWOOD FLOORING INSTALLATION - GENERAL REQUIREMENTS

.01 General:
  • Regardless of the installation method chosen, proper preparation and the use of skilled installers is necessary for a satisfactory finished appearance and the performance of hardwood flooring and related accessories.
  • Most floor covering contractors employ skilled installers who recognize the importance of following proper procedures to assure both the best appearance and the best performance of the finished installation. This means careful attention must be given to the proper preparation of substrates, a properly planned installation layout to assure flooring material grain and pattern match, pre-conditioning of hardwood flooring materials, the use of correct installation procedures and techniques, and finally in the case of site finished material, the choice and application of an appropriate finish. The hardwood manufacturer's recommended installation procedures must be followed or the manufacturer will reserve the right to withhold any guarantee unless there is rigid adherence to such procedures.
  • Part of any installation is the choice and use of the correct tools and installation materials to suit the particular installation.
  • Prior to installation the hardwood flooring manufacturer as well as any flooring installation material manufacturers (such as underlayments and adhesive if used) must be consulted in regard to their recommendations for the installation of their materials. Only methods and materials specifically designed for the installation method selected shall be used.

.02 Tools and Installation Materials:

  • All hardwood flooring and accessories shall be installed using tools and materials recommended by the material manufacturers and as referenced in this standard.

  • Proper tools and quality materials are essential for a skilled and proficient installation of hardwood flooring.

  • All required tools should be on the job site for the complete duration of installation work to assure a uniform and correct installation.

.03 Acceptable Substrates and Site Conditions:

  • Refer to Part A10 - Acceptable Conditions, for acceptable substrate types and environmental conditions for the installation of hardwood flooring materials.

  • Unless otherwise specified or agreed to prior to Bidding or installation, the General Contractor / Construction Manager, or Owner is responsible for providing acceptable substrates and site conditions for the installation of hardwood flooring and related materials.

  • All site and substrate surface conditions and their preparation shall be in accordance with the hardwood flooring material manufacturer's recommendations and NFCA requirements as noted in Part A10 - Acceptable Conditions.
  • Note: Hardwood flooring when installed over an uneven substrate surface (including depressions and protrusions) may result in squeaking floors and cause premature surface wear. As well, soil, dust, wax, oil, grease, moisture, and other contaminants on the substrate can prevent or otherwise destroy adhesion for flooring that is adhered directly to the substrate causing localized or widespread failure.

    • Where hardwood flooring is to be installed over crawl spaces, unheated basements, or below grade (when approved by NFCA) such spaces must be dry and well ventilated. In joist construction the joists should be insulated from below and when over crawl spaces, outside cross ventilation through vents or other openings in the foundation walls must be provided with no dead air areas. A surface cover of 0.15 mm (6 mil) polyethylene film is essential as a vapour retarder in crawl space construction.
    • Where hardwood flooring is to be installed over concrete, all concrete substrate surfaces shall be tested for moisture and alkalinity in accordance with floor covering material manufacturer's recommendations and as noted in Part A11 - Substrate Testing. All other substrate surfaces shall be tested for moisture as applicable in accordance with these requirements.

    • All site conditions, installation requirements, and the timetable for the work shall be reviewed. Substrates, environmental conditions, and work by other trades shall be acceptable prior to commencing any installation of hardwood flooring and to ensure that the schedule for installing such flooring can be maintained.

    • Any existing floor covering materials, including adhesive, shall be removed and recycled or disposed of in a legal manner.

    • All substrate surfaces to receive hardwood flooring shall be clean, dry, smooth, and free from all substances detrimental to fillers and patching compounds where required and to adhesive bond where flooring materials will be glued to such surfaces. Surfaces shall be vacuumed clean.

    • Hardwood flooring shall only be installed over substrates that are acceptable to and are prepared in accordance with NFCA requirements and specific product manufacturers recommendations for the type of flooring materials and specific installation methods selected.

    • Patching and filling of substrates shall be in accordance with extent / limits and requirements of Part A13 - Patching and Filling. Where used, patching compounds must be polymer-fortified, suitable for the intended application, and be applied in strict accordance with the patching material manufacturer's instructions and NFCA requirements noted in Part A13. If required by the patching compound or adhesive manufacturer, patched areas shall be primed and/or sealed, particularly if they are porous and highly alkaline, which may prevent adequate adhesive bond where flooring is glued.
    • Where level discrepancies are too large, i.e. where the thickness of patching and filling compounds required exceeds NFCA tolerances, such surfaces must be corrected by others using a self-levelling cementitious underlayment in accordance with requirements of Part A13 - Patching and Filling.

    • All substrates must be structurally sound so as to not compromise the hardwood flooring installation. Unless otherwise agreed to prior to commencing work all structural deficiencies must be corrected by others before any hardwood flooring is installed.

    • All defects likely to impair flooring work shall be reported to the General Contractor / Construction Manager and Owner in writing. Hardwood flooring installation shall not proceed until all deficiencies and unsatisfactory environmental and site conditions have been corrected.

    • Installing hardwood flooring prematurely before other trades have completed their work or in the presence of personnel not essential to the flooring installation often results in visible damage and soiling. These conditions may not be immediately evident.

    .04 Planning and Layout:
    • All facets of hardwood flooring installation shall be carefully coordinated before ordering materials.

    • To aid in the estimation / Bidding and ordering / installation of hardwood flooring and related materials site measurements are required.

    • In large sized commercial and institutional or complicated projects, scaled drawings should be prepared using actual site measurements for both new construction or existing areas in order to determine quantities and types of materials (flooring, underlayments, moulding and trim, etc.) to be installed, to identify orientation of flooring, and to provide details as required.
    • In all cases the following shall be considered:

      • Strip / plank direction in each area.

      • Pattern layouts where applicable.

      • Quantity of flooring required for each area allowing for method of product packaging and unusable material in each carton, bundle, or nested bundle.

      • Quantity of underlayment required for each area, including roll length requirements.

    .05 Shop Drawings (installation / layout drawings where required):
    • Where specified, the hardwood flooring supplier / contractor shall provide shop drawings to the design authority through the General Contractor / Construction Manager or Owner for pre-approval in accordance with specification submittal requirements. This is generally a requirement for large-scale commercial and institutional projects only and is not necessary or normally required for residential or small-scale projects.

    • Shop drawings shall be prepared from actual site measurements for each floor area to receive hardwood flooring. Do not scale the design authority's drawings or calculate sizes from drawing dimensions shown.

    • Shop drawings shall contain the following information:

      • Room and floor numbers (based on drawing information and Finish Schedules provided by the design authority when applicable).

      • Type of substrate and installation method for each area and floor preparation required.

      • Type of underlayment required for each area, including roll length requirements, i.e., a cut list.

      • The species, grade, stain, flooring type (e.g. strip, plank, etc.), and direction / pattern of hardwood flooring for each area.

      • Type and locations of all base, trim, and mouldings within each area.

      • Large scale detail drawings where required (hardwood stairs, etc.).

    • Shop drawings shall also include the following additional information as appropriate:

      • Name and address of the project (building).

      • Name, address, and phone, facsimile, and email numbers of the Owner.

      • In new or renovation construction, the name, address, and phone, facsimile, and email numbers of the design authority (e.g. architectural or interior design firm) and the General Contractor or Construction Manager.

      • Name, address, and phone, facsimile, and email numbers of the hardwood flooring supplier and installation company.

      • Date of drawing and scale.

      • Party responsible for removing furniture and oversize items in existing areas.

      • Party responsible for removing and disposal of existing floor covering materials in existing areas.

    .06 Material Choices:
    • The following factors affect the choice of hardwood flooring to be installed:
      • All solid wood flooring will expand with changes in moisture content and the wider the board, the greater the potential for gaps between the boards when they experience seasonal humidity and temperature changes. 
      • Boards with beveled edges will help to disguise inevitable shrinkage and individual board movement. 
      • For solid wood flooring products, Quarter cut, Rift, or Edge Grain materials are more stable than their flat or plain sawn counterparts.
      • For installations of hardwood over in floor heating systems, check with the manufacturer to confirm suitability warranty of the hardwood product.
      • Many wood floor finishes scratch white. Darker colored wood floors in high traffic areas should be be carefully considered.
      • Softer wood species dent and compress easily and may not be suitable for high traffic applications. Refer online to a wood hardness chart for comparison to other species.

    .07 Ordering Materials:
    • As hardwood is a natural product manufactured according to industry standards that permit a defect tolerance not to exceed 5% of the square footage, additional material must be ordered. These defects may be of a natural or manufacturing origin.
    • Typical cutting waste of 5% should be added to orders of unfinished solid wood flooring.
    • Engineered flooring installed in the floating method will require more material to be ordered.
    • Wider planks produce more cutting waste.
    • Wood flooring installed on a 45 degree angle produces considerably more cutting waste. Careful calculations should be made for accurate ordering.
    • Herringbone patterns require considerably more material be ordered for cutting waste. 
    • Waste quantities depend on the size of the projects, complexity of layout and size of individual planks.
    • No one waste percentage amount applies to all scenarios.

    .08 Material Delivery, Handling, and Storage:
    • All hardwood flooring and related installation materials shall be delivered, handled, and stored in strict accordance with material manufacturer's requirements and in a manner to prevent damage or distortion to the materials.

    • As a kiln dried material with a moisture content of 6 to 9%, hardwood flooring shall be delivered from the point of manufacturing to the jobsite fully protected from damage and exposure to the elements. Protection shall not be removed and material shall not be unloaded in rain, snow, or excessively humid conditions, nor shall it be stored in excessively dry heat conditions. Such conditions may result in moisture absorption and swelling of wood or over drying and shrinking of materials. This will cause buckled flooring or shrinkage when the material is installed without proper acclimatization or adequate expansion gaps.

    • All materials shall be stored on site and adequately protected from dirt, dust, moisture, and other contaminants, in secure, climate-controlled, dry spaces within manufacturer's written temperature and humidity requirements. Under no circumstances shall such materials be moved to and/or stored in unconditioned spaces.
    • New construction shall be closed in with outside windows and doors in place and all concrete, masonry, gypsum board, and framing members shall be thoroughly dry before flooring materials are delivered to the job site. The average moisture content of wood framing members and sub-flooring should be below 14% before delivery of any flooring materials as a moisture content above this level may cause moisture related problems. Knowing the moisture content of substrates prior to the installation of flooring is essential to its performance.
    • Tests must be conducted and digitally recorded (photographed) to confirm moisture level of sub-floor and substrates are in accordance with NFCA requirements (refer to Part A11 - Substrate Testing). Test results are to be verified by the flooring installer in each area. Where moisture conditions are above manufacturer and NFCA requirements delivery of hardwood flooring to job-site shall not proceed.

    • As noted, flooring materials are manufactured and supplied with a moisture content between 6% to 9%. The moisture content variation between the sub-floor and flooring material should be less than 4% with 57 mm (2 1/4") material and 3% with 83 mm (3 1/4") material. Flooring must not be installed when the substrate moisture content is above 12% for hardwood flooring and 14% for engineered flooring or above the variation levels noted above unless otherwise permitted by the hardwood and engineered flooring manufacturers. These moisture levels must be verified on site using a recently calibrated, pin type wood moisture meter.

    • Caution: Flooring materials must not be delivered or acclimatized on site when environmental conditions are not within required moisture, humidity, and temperature levels.

      • Most hardwood flooring manufacturers have high manufacturing standards and stringent inspection procedures for their finished products. Nevertheless, all hardwood flooring materials should be inspected upon delivery and before installation by the General Contractor / Construction Manager or Owner and the Supplier Representative (and Design / Consultant if required) to confirm product grade and quality and if any suspected irregularities are noted that might give rise to undesirable visual effects, installation should not proceed until the supplier has also inspected the material and an agreed upon course of action has been established. 
.09 Conditioning
  • All hardwood flooring, adhesive, underlayment and related materials shall be conditioned or acclimatized within the area of installation and be adequately protected from soil, dust, moisture, and other contaminants during this time. Where possible the conditioning period shall be for at least 48 hours before installation, or as a minimum, at least until the materials reach temperature and humidity levels of the installation area, providing they are within requirements noted herein.
  • To facilitate conditioning, solid hardwood flooring bundles and packaged wrappings shall be opened and removed if required or recommended by the manufacturer and the material separated into small lots and stored in areas where it will be installed ensuring that there is adequate room around stacks of material for good air circulation.
  • Plastic wrapped Engineered hardwood flooring materials should be left in packaging until ready for installation. Where possible the conditioning period shall be for a minimum of 4 to 5 days in correct conditions before installation.
Prior to installation:
  • Hardwood flooring product shall be tested for acceptable moisture content.
  • Hardwood flooring packages shall be tested for acceptable temperature.
  • Sub-floor surface shall be tested for acceptable temperature, and moisture content.
  • Ambient room temperature and ambient room Relative Humidity shall be tested, recorded and confirmed acceptable to manufacturers requirements.
  • Test results shall be recorded for ease of reference at a future date should an issue develop.
Failure to acclimatize (condition) hardwood flooring correct may result in:
  • dimensional changes.
  • excessive expansion.
  • development of squeaks and creaks.
  • Veneer face checking.
 
Note: In all cases manufacturers requirements for conditioning shall apply.

  • Areas in which hardwood flooring is to be installed must be heated and ventilated and the ambient and substrate temperatures and humidity levels must be within the flooring and installation material manufacturers requirements. Unless otherwise specified by the hardwood flooring manufacturer the ambient temperature shall be between 16°C to 27°C (60°F to 80°F) and the relative humidity shall be between 30% and 50%. Unless otherwise approved by the manufacturers the minimum substrate (notably concrete) temperature shall be not less than 16°C (60°F).
  • Note: If the temperature and humidity levels are outside these parameters, the installation must not begin until the heating and ventilation system (and air conditioning system if an option) is operational and the temperature and humidity level reaches minimum manufacturer and NFCA requirements and is maintained for a minimum of 72 hours before, during, and at least 72 hours after the installation.

    • From the time flooring is delivered and until occupancy, temperature and humidity levels must be maintained at or near occupancy levels. After occupancy the environmental conditions must be controlled so as to maintain the heat and humidity levels at a constant level within the ranges noted. Extended times without such controls can adversely affect hardwood flooring.
    • Installed hardwood flooring must also be protected from excessive heat. Flooring installed over a heating pad and/or un-insulated heating ducts and piping may develop cracks unless protection from the heat is provided. It is therefore critical that any concentrated heat source be separated from hardwood flooring. This can be accomplished by the use of a suitable insulation around or above (i.e., between joists) heating ducts and piping in these areas. The insulation should be non-combustible where required.
    • For site requirements in regard to radiant heated floors refer to item 3.06 below.
.10 Floor Protection
  • Installed flooring shall be protected with heavy Kraft-paper or other suitable covering as recommended by the flooring manufacturer. Do not use non-breathable sheet or film that could cause condensation to form. This covering must be maintained throughout the remainder of construction period.
  • Protective sheathing should be overlapped and taped. At no point should tape of any kind, unless approved by the manufacturer, touch or stick to the wood floor finish.
  • The overall responsibility for the protection of all installed hardwood flooring, from completion of work until the Owner's take-over, is the responsibility of the General Contractor. The flooring contractor will not be able to control the work or actions of on-site workers, or the actions of persons causing damage from setting-up or delivering equipment, furniture, or other items to the site.
2 • HARDWOOD FLOORING INSTALLATION METHODS

.01 A variety of methods are used to install hardwood flooring to acceptable substrate surfaces. Typically solid hardwood strip, plank, and parquet flooring are recommended to be installed on or above grade and engineered hardwood strip, plank, and parquet flooring can be installed at all levels of the building.

.02 Refer to relevant Association (e.g. CLA, NWFA/NOFMA, MFMA, SPIB) guidelines for acceptable methods and specific installation requirements for hardwood flooring materials and systems. The following is offered as general information only:

.03  Nail Down Installations: This method uses hand or power driven nailing tools to attach solid strip or plank tongue and groove flooring to acceptable wood substrate (sub-floor)       surfaces using special "L" or "T" shaped nails, barbed cleats, or staples for flooring driven through the tongue of each piece at prescribed intervals with the groove of the                   following piece of flooring concealing the fasteners. Pneumatic nailing machines designed for hardwood flooring installation that use fasteners fed into the machine in clips may       be used to drive fasteners through the tongue of the flooring at the proper angle.
Link to recommended nailing schedules.
Solid and engineered flooring products can be nailed into place. In all cases manufacturers require 15 gauge fasteners and state strict nailing schedules be followed.
.04 Full Spread Glue Down Installations: This method uses mastic or adhesive to adhere solid hardwood flooring to an acceptable wood or concrete substrate. As there are many types of adhesives and mastics on the market it is important to use the flooring manufacturer's recommended adhesive or mastic, trowel size, and spread rate when installing flooring. Not doing so can cause issues and could void any product warranty.
Full spread glue down installations create a solid feel to the floor under foot and are quieter to walk on than a floating floor design. Care must be taken to use the correct adhesive type and trowel size. Sub-floors must be flat to manufacturers recommendations (see below).
Note: The use of mastics (a petroleum based material) may now be limited due to environmental issues (VOC's and off-gassing). The use of such material must be verified with the design professional, with authorities having jurisdiction and the flooring manufacturer / supplier.
.05  Glueless Floating Installations:
This method for engineered hardwood flooring utilizes the product manufacturer's proprietary glue-less fastening system to connect flooring pieces (planks or panels) together by friction or mechanical means only.
.06 Glued Joint Floating Installations:

This method for engineered hardwood flooring utilizes glue to connect engineered hardwood units (planks or panels) together. The glue is applied to the tongue and groove on site or in some instances the manufacturer may have a proprietary pre-glued joint system.
Note that the type of adhesive may be subject to environmental issues and LEED requirements.
  • Floating Floors: Floating floors, by design, are meant to "float", unrestricted in a way that allows them to expand and contract naturally as indoor environmental conditions change. They can do this on a variety of acceptable substrate surfaces such as wood sub-floors, concrete slabs, and even some types of existing floors. Floating floors must not be anchored in anyway to the sub-floor below.
  • Overlap transitions: Transitions must be carefully installed to allow natural expansion and contraction of the wood flooring.
               T Caps - End Caps - Reducer Strips - Overlap Bull Nosings - Quarter Round are all different wood moldings used for transitioning wood flooring to other floor coverings.
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Incorrect application of adhesive
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'T' Cap Expansion Joint
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Overlap Reducer
  • Under pad - Floating floors are usually installed over a separation membrane or a resilient / acoustical underlayment. Refer to Part D03C - Material Guide - Flooring for various types of underlayments and their usage.
.07 Sports Flooring Installations: These solid hardwood flooring installations encompass some of the above noted methods in part or in whole and include various resilient             sub-assemblies to provide a sprung flooring system to meet specific design parameters. These installations are typically proprietary systems and can be installed over a variety       of substrate surfaces.
3 • INSTALLATION REQUIREMENTS

.01 Substrate Level Tolerances:

  • Hardwood flooring must be installed over acceptable substrate surfaces that meet specific level tolerances. Notwithstanding concrete slab and floor finish classifications and level tolerances noted in current CSA A23.1, ATSM E1155, or ASTM E1486 consensus standards, or those required by MFMA, NOFMA, or other wood flooring associations the substrate finish classifications and level tolerances required by NFCA for all types of substrates (including concrete slabs-on-grade, suspended concrete, wood and other substrate types noted herein) at the time of floor covering installation shall be as follows:
Refer to Part A10 - Acceptable Conditions for further clarification.
.02 Substrate Moisture Control and Testing:
  • When hardwood flooring will be installed over on-grade or below grade concrete slabs or over unheated and un-ventilated spaces there is danger of dampness and condensation affecting the hardwood flooring.

  • New concrete contains water which is problematic for wood flooring. Proper on-grade slab construction requires a free draining support layer (e.g., compacted granular fill) and a vapour retarder between the fill and the slab as noted below. While this prevents moisture entry through the slab, this membrane also retards the curing of the slab.

  • To be absolutely certain moisture does not reach hardwood flooring installed over concrete substrates on or below grade, a vapor retarding membrane must be used. Where this is placed will depend on the type of system used.
For on-grade concrete slab construction a 0.15 mm (6 mil) polyethylene or other membrane waterproofing barrier should be installed over the compacted granular fill (as noted above) and directly under the slab (this is usually provided by the General Contractor). In addition adequate drain tile should be provided adjacent to the footings, and in colder areas perimeter insulation is highly recommended to prevent cold transfer and freezing / thawing of the fill and slab.

Supplementing the membrane waterproofing barrier, concrete slab surfaces should be damp-proofed with one ply of 30 lb. or two plies of 15 lb. asphalt saturated felt, each laid in a heavy trowel coating of mastic with edges butted and surfaces rolled to remove air pockets and blisters. Alternatively a layer of 0.15 mm (6 mil) polyethylene with joints lapped minimum of 100 mm (4") may be used. This damp-proofing is usually provided by the wood flooring Contractor.
  • A suspended concrete slab with a controlled environment below does not require a surface vapor retarder.

  • A suspended slab over exposed earth or an uncontrolled environment below requires a proper vapor retarder over the slab surface. In this case cross ventilation below the slab is essential, and, if over exposed earth, a 1.5 mm (6 mil) polyethylene ground covering should be provided.

  • It is important to note that the appearance of any new or existing concrete slab can be deceiving and it is never safe to assume that it is dry. Accordingly all new and existing on-grade or suspended concrete substrates shall be tested by an independent testing agency for moisture content and alkalinity levels in accordance with the requirements of Part A11 - Substrate Testing. The testing methods employed must be acceptable to the flooring manufacturer before testing. Such testing must be conducted at several locations in each area, room, or floor level. Test results must show acceptable conditions before commencement of any hardwood flooring installation.
  • Where moisture tests have been conducted and documented and show acceptable conditions at the time of application, subsequent failure of the hardwood flooring application due to the presence of moisture, failure of membrane waterproofing or damp proofing will not be the responsibility of the hardwood flooring contractor. Repairs to the hardwood flooring as a result of such moisture problems, will be the responsibility of the General Contractor / Construction Manager or Owner.
.03 Hardwood Flooring over Concrete Substrates:
  • Solid and engineered hardwood flooring can be installed successfully on suspended and above grade concrete slabs and on slabs-on-grade. Below grade installations are not recommended for solid hardwood flooring because of costlier substrate preparation requirements but may be acceptable for engineered hardwood flooring subject to manufacturers requirements and pre-approval.
  • All suitable concrete substrates must be dry, sound, and level with a smooth trowel finish to a Concrete Surface Profile of 1 to 2, and be free of curing agents, sealers, grease, oils, paint, stains, and dust. Any high spots should be ground smooth and low spots filled and slab swept clean. Refer to Part A10 - Acceptable Conditions.

  • As previously noted in 3.01 the use of a moisture-retarding barrier for on or below grade concrete slabs is imperative and the use of a separation barrier between any wood members and concrete at any level is also recommended.

.04 Hardwood Flooring over Wood Substrates:
  • In all of the following cases, solid and engineered hardwood flooring installed over wood substrates shall conform to flooring manufacturer's recommendations and NFCA minimum requirements.
  • 3/4" solid t&g wood flooring:  When joist spacing is at 16” (406mm) o/c or less, the industry standard for single-panel subflooring is nominal 5/8” (19/32”, 15.1mm) CD Exposure 1 Plywood subfloor panels or 23/32 (18.3mm) OSB (Oriented Strand Board) subfloor panels, 4’ X 8' sheets.

  • Plywood over Concrete Substrates: This system utilizes 19 mm (3/4") or thicker sheathing grade exterior plywood installed over a vapour retarder membrane and mechanically fastened to the concrete slab-on-grade or suspended concrete slab using powder activated or hammer driven concrete nails. Refer to NOFMA for specific details and requirements. This method is not often used and not recommended in multi-residential construction where sound transmission through fasteners is a concern.
  • Screed System on Concrete Substrates: This system uses pressure treated wood screeds or sleepers of random lengths laid at right angles to the direction of the finished flooring and set in adhesive over acceptable concrete substrates. The flooring is installed over a vapor retarder spread over the screeds. As a general rule, the screed system alone is used for all 19 mm (3/4") strip and plank flooring up to 100 mm (4") wide. Plank flooring 100 mm (4") and wider requires either a plywood-on-slab sub-floor or screeds plus a wood sub-floor to provide an adequate nailing surface. The sub-floor may be 16 mm (5/8") or thicker plywood or 19 mm (3/4") boards no wider than 150 mm (6"). In all cases refer to NWFA/NOFMA for specific details and requirements.
  • Installation over Wood Framed Systems (joists and sub-flooring): This system uses plywood or other suitable sub-floor panel sheathing over wood joists with the sheathing panel face grain laid at right angles to joists and fastened using appropriately spaced fasteners. The thickness of panel sheathing is subject to joist spacing and load conditions but in any case should not be less than 16 mm (5/8") thick. It is also recommended (although not part of flooring work) that the sub-floor sheathing be glued and screwed to the joists when possible to eliminate floor squeaks and movement.
  •  Outside cross ventilation through vents or other openings in the foundation walls with no dead air areas must be provided. Over a crawl space, a ground cover of 0.15 mm (6   mil) polyethylene film or concrete skim coat shall be provided as a moisture barrier.

    Note: NFCA does not recommend non-veneered panel products for sub-floors.

    • In addition, and where required by the hardwood flooring manufacturer, a separation membrane (such as building paper) may also be required between the substrate and hardwood flooring to keep out dust, retard moisture movement from below, and to help prevent squeaks in dry seasons.
.05 Hardwood Flooring Over Existing Wood Flooring:
  • Existing wood floors can serve as substrates for the installation of new solid or engineered hardwood flooring provided they meet flooring manufacturer and NFCA minimum requirements for installation. Any raised nails must be driven down, loose and warped boards replaced, and floor surfaces vacuum / swept clean without the use of water.

  • Where the flooring is to be glued down, the existing surface must be cleaned, screened (lightly sanded), and vacuumed to provide a smooth, level, roughened and dust free surface acceptable for adhesive application. In some instances flooring manufacturers may recommend a thin panel overlayment be installed over the existing floor, although this will add to the overall height of the floor installation.
  • Where the flooring is to be nailed down the use of a separation or slip-sheet may be used as recommended by the flooring manufacturer to eliminate dust and moisture transmission and squeaks caused by new flooring binding with the existing floor boards.

  • Where flooring is to be "floated" (not fastened) over existing wood flooring the existing surface must be acceptable for the installation of flooring and resilient / acoustical underlayment.

  • Existing doors and baseboards must be removed and thresholds must be removed to allow new flooring to run flush through doorways and to provide an expansion gap under the reinstalled existing or new base.

  • It is strongly recommended that new flooring be installed at right angles to old floor boards, although this may not always be possible.

.06 Hardwood Flooring Over Radiant In-Floor or Below Floor Heating:

  • As a general rule most hardwood flooring manufacturers do not recommend nor will they warrant the installation of solid hardwood flooring over radiant heated floors (due to the risk of excessive shrinkage) but will recommend and warranty engineered flooring over such heating. The hardwood flooring manufacturer must be consulted for any restrictions. Refer also to Part D03C - Material Guide - Flooring, item 14.
  • There are a variety of radiant heating systems. Some of these include heating elements (piping) installed within the concrete slab or concrete topping, between a plywood sub-floor and a wood flooring panel system on sleepers, or affixed to the underside of wood sub-flooring. Some systems are not suitable for the installation of hardwood flooring.
  • In all cases where any type of hardwood flooring is installed over a radiant heating system the following precautions must be adhered to:

    • The substrate (slab, sub-floor, and sleepers) must be tested for moisture and confirmed dry or within moisture content levels acceptable to the flooring manufacturer and NFCA.

    • The flooring installation must strictly adhere to the flooring manufacturer's requirements for radiant heated substrates, noting that any flooring materials such as plywood, sleepers, or flooring cannot be fastened to the concrete (i.e. nails and powder-actuated fasteners are not permitted). Note also that particle board subfloors are not recommended by radiant heat companies.

    • The hardwood flooring must not be installed in direct contact with radiant heating elements or coils or over green concrete or wet sub-floor sheathing.

    • The radiant heating system should be running at 20°C (68°F) for two weeks (or at least 5 days) prior to delivery of wood flooring to the site to drive moisture out of the substrate (e.g. slab) and to acclimatize the installation area. Both the flooring and adhesive manufacturers should be consulted to determine if the radiant heating system needs to be turned off and the flooring installed on a cool substrate or if it should remain on throughout the installation process. Where the heating system is not operational or is turned off and the hardwood flooring is installed on a cool substrate surface, the heat should be turned on after the installation and be slowly increased until service temperature has been reached. This must be done gradually in 5°C (15°F) increments at a time so as to avoid unnecessarily shocking the floor with a sudden heat loss or gain.

    • Thermostat controls must be fully operational to avoid overheating the floor.
    • A protective covering of building paper or other material pre-approved by the flooring material manufacturer should be installed over the flooring after installation until occupancy.

  • The following factors may affect hardwood flooring installed over radiant heated substrates after installation:

    • Wood flooring is an insulator and may require higher water temperatures than for other types of flooring (e.g. carpet).

    • The heating, ventilation, and air conditioning (HVAC) system should have an automatic humidity control in order to keep the relative humidity of the area at an even level. This will keep the equilibrium moisture content of the floor stable.

    • An outside thermostat is recommended to respond to rapid temperature changes resulting from outside sources (e.g. sun through windows) and to protect the perimeter of the system from condensation absorption during the spring and fall when rapid temperature changes may occur.

    • Radiant heating water temperature must be controlled to keep it to a maximum of 52°C (125°F). This will limit the temperature of the slab surface to about 29°C (85°F), which is an acceptable level for most adhesives and mastics.

    • Wood dries rapidly when any heat is first turned on and will dry to a lower moisture content toward the end of a heating season. When radiant heat is turned off (e.g. during warmer summer months) moisture will once again start to seep into the concrete or wood sub-floor over crawl spaces and the hardwood flooring. Abruptly turning on radiant heating at the start of cooler months (Fall) will subject wood flooring to rapid and easily noticed movement which may cause cupping or crowning of the flooring and/or shrinkage cracks between individual floor boards. Turning on the heat in small increments will slowly acclimatize the floor resulting in less stress and movement in the floor. Humidity controls can help to offset flooring expansion and contraction by maintaining a constant humidity level throughout the year.
.07 Hardwood Flooring Expansion:

  • Most complaints concerning hardwood flooring are related to changes in the moisture content of the flooring. When moisture changes are severe, the result can be gaps between strips / planks, cupping, buckling, movement, and/or cracks/splits in the flooring. A combination of these results may be present in the same floor.

  • As wood is a hygroscopic material, it will absorb or release moisture when exposed to the air. Exchange of moisture vapor between the wood and its surrounding environment will continue until equilibrium with Relative Humidity and temperature are achieved.
  • Moisture absorption causes wood to swell. Shrinkage of wood begins at 25 to 30% moisture content, the fiber saturation point, and will continue until it reaches 0% moisture content, an oven-dry state. Conversely, swelling occurs as wood increases in moisture content from 0% to 25-30% moisture content, the fiber saturation point. Above 25% to 30% wood is dimensionally stable.

  • Wood does not shrink or swell equally in all directions. A change in moisture content of a piece of wood from 0% to 28% (oven dry to fiber saturation point) will increase the size of the piece approximately 0.1% longitudinally or along the length / grain, 2% to 8% perpendicular to the annular growth rings (radially or in strip width for quarter sawn flooring), and 5% to 15% change in size parallel to the tree's annular growth rings (also known as tangentially or in width of the strip with plain sawn flooring).

  • The shrinking and swelling of wood depends on a number of conditions in the area of installation:
    • Incomplete construction such as concrete, masonry, gypsum board, paint. 
    • Moisture content of substrate systems and moisture conditions at the job-site. 
    • Moisture content of flooring at the time of delivery. 
    • Expected moisture content of wood flooring in a particular area after acclimation and installation.
    • Ambient Relative Humidity, Temperature and the particular wood species expansion/contraction coefficient 
    • Type and operation of the HVAC system.
    • Type and operation of the heating system.  
    • Geographical area and the time of year.
  • As a general rule, engineered hardwood flooring is less susceptible to dimensional changes due to humidity fluctuations than solid hardwood flooring.
  • Expansion Allowance: An allowance for expansion must be left around the perimeter of the installation area as well as at all vertical interfaces such as millwork, around columns, transitions to other floor coverings etc. The size of an expansion gap must comply with the manufacturers recommendations.
  • Expansion will depend on a number of factors:
  • The type of material (solid or engineered strip, plank, or parquet hardwood).
  • The species of wood. (Some species are less stable than others and will shrink or expand more than other species).
  • The direction of installation.
  • The environmental conditions of the project (some areas have higher humidity and temperature variations than others). Generally, wood flooring is expected to expand in wetter climates or when it is exposed to wet conditions and shrink in dry climates or when it is exposed to dry conditions.
  • The moisture content (i.e., the larger the change of moisture content; the larger the change of width between oven-dry at 0% and fibre saturation at 28%.
  • The direction of grain (plain sawn material will change more than quarter sawn material).
  • Wider pieces of flooring will shrink or expand more than narrow pieces of flooring for a given change in moisture content. Four strips of 38 mm (1 1/2") flooring will expand / contract as much as two strips of 75 mm (3") flooring under similar conditions, species, grain, and pattern.
  • In all cases, the width of the gap left for expansion shall be in accordance with the above noted factors and the manufacturer's recommendations for the material and actual site conditions that apply.
  • Depending on the requirements and width of gap, a wood base, vent cove rubber base available from resilient flooring manufacturers, or other similar detail acceptable to the designer and flooring manufacturer may be used as a perimeter molding over the expansion void. The base is attached to the walls only.
  • Heavy items on floating hardwood floors.
Expansion / movement restriction:

Floating Hardwood floors must be allowed to move (shrink/expand) naturally through the four season cycle and with natural changes in ambient Relative Humidity. Excessive loads on the floor can restrict such movement. Recommendations for load capacity regarding Kitchen Islands, commercial refrigerators, grand pianos or other heavy items that may restrict movement should be obtained from the flooring manufacturer. A 500 lbs maximum is a general guide only.
Each hardwood product manufacturer should be consulted for technical guidance regarding weight restrictions.
Tension in joints caused by restricted movement can lead to squeaks.

4 INSTALLATION OF HARDWOOD FLOORING

.01 General Requirements: The following applies to hardwood strip and plank flooring installed on plywood-on-slab, on screeds, and on plywood or board sub-floors.

.01 Acceptable Surfaces and Level Tolerances: as noted herein.

.02 Wood Substrates: Where a plywood or board sub-floor is used, any loose areas should be re-screwed and the sub-floor swept clean. Wood substrates shall be covered with a separation sheet (e.g. building paper) with 100 mm (4") lapped seams with the type of paper as recommended by the flooring manufacturer. This helps keep out dust, retards moisture from below, and helps prevent squeaks in dry seasons.
.03 Direction of Finish Flooring: For best appearance, strip and plank flooring should be laid in the direction of the longest dimension of the room or area and where possible across or at right angles to joists. If installed parallel to joists an increase in sub-floor sheathing or additional joist bracing may be required.

.04 Dry Laying or Racking the Floor: Seven or eight loose rows of strip or plank flooring should be laid out end to end in staggered pattern with end joints at least 150 mm (6") apart. Multiple bundles or packages should be used for this purpose to ensure an equal blending of material and to check for appearance (grain and colour variation). Care should also be taken to ensure an even distribution of long and short pieces and to avoid clusters of short boards.
.05 Layout Lines: Walls may not be square or in line and they should not be used as working lines for the installation of hardwood strip, plank, and tile./ parquet flooring unless their squareness and alignment is verified and compensated for before commencement of installation of any flooring. All flooring shall therefore be installed working from chalk lines established in accordance with flooring manufacturer's recommendations and NFCA requirements.
.06 Commencement of Laying: The location and straight alignment of the first strip, plank, or tile is important. It is imperative that they be installed square and aligned with chalk layout lines. Subsequent material adjacent to the starter row should fit tightly.
.07 Fastening: All fastening of solid and engineered hardwood strip, plank and parquet flooring shall be done in strict accordance with manufacturer's recommendations and NFCA minimum requirements for substrate conditions that apply. The following must be considered:
  • Good fastening is important as it limits movement and keeps the boards rigid preventing creeping / creaking sometimes caused by shrinkage in sub-floor lumber. Without adequate fastening it is impossible to obtain solid, non-squeaking floors.
  • Tongue and groove flooring shall be blind nailed through the tongue according to manufacturer's recommendations and NFCA minimum requirements. The first board should be set on the chalked line with the groove side towards the wall and face nailed with finishing nails at one end of the board near the grooved edge such that the nails will be covered with the base shoe.
  • Square edge (non T&G) boards shall be face nailed with countersunk fasteners and holes filled with appropriate filler according to manufacturer's recommendations and NFCA minimum requirements. Pre-drilling nail holes may be required to prevent splits.
  • Various manual and pneumatic "nailing" machines using either a barbed fastener or staples fed into the machine in clips may be used with the fasteners driven through the tongue of the flooring at the proper angle.
  • Note: As not all wood flooring manufacturers recommend the same nailer or stapler gun, it is important to read the manufacturers installation manual to assure that the right type and size of staples are used.
  • Caution: Improper pressure settings and failure to use proper adapters can cause severe damage or dimpling on the board face while power nailing or stapling hardwood flooring. The correct adapter and air pressure setting will properly set the nail, brad, or staple in the nail pocket. Low air pressures may fail to properly set the nail, brad, or staple and damage adjoining boards. High air pressures may cause damage to the tongue preventing installation of adjoining boards and can also cause blisters on the face of the flooring. Installers must make certain that the equipment used is designed for the type of flooring being installed and for the type of fastener selected. The equipment compressor must have an in-line regulator for proper adjustment. Power nailing or stapling equipment shall be set at the air pressure rating recommended by the flooring manufacturer for the type of flooring, nail, brad, or staple and substrate types, and shall be adjusted until the correct nail or staple setting occurs. Any water damaged, swollen or delaminated sub-flooring materials will not properly hold nails or staples and must be repaired or replaced. Some flooring manufacturers suggest that minor squeaking of stapled floors is not abnormal due to structural movement caused by environmental conditions.
  • Warning: Improper stapling / nailing can cause dimpling on the face of flooring due to improper adjustment of the stapler / nailer shoe and angle / place of staple entry. To counter this, fastening must always be visually checked at a low viewing angle under good lighting conditions and from a distance as work progresses to ensure that dimpling does not occur.
  • Nailing to Screeds: When nailing directly to screeds 9no solid sub-floor), nailing shouldoccur at all screed intersections and at both screeds where a strip passes over lapped screed joint. Since flooring ends are tongued and grooved, all end joints do not need to meet over screeds but end joints of adjacent strips should not break over the same void between screeds.
  • Wall Base and Quarter Round or Shoe Molding: The base must be fastened to the wall with the quarter round or shoe molding nailed to the baseboard and not the flooring, after the entire floor is in place.
.8  Adhesives: Where hardwood flooring is to be glued down it shall be installed over clean and acceptable substrate surfaces using adhesives / mastics applied at coverage rates with notched trowels all in strict accordance with manufacturer's requirements. Refer to 2.04 above for additional requirements.
.02 Installation of Hardwood Strip Flooring:
  • Hardwood strip flooring laid on plywood-on-slab, on screeds, and plywood or board sub-floors shall be installed in strict accordance with hardwood flooring manufacturer's recommendations and NFCA minimum requirements.
  • Note: Flooring "Shorts", i.e. 380 mm or 610 mm (1-1/4' or 2') bundles of flooring strips are Strip Flooring and should be installed as such.
Note: When using a nailing machine to fasten 19 mm (3/4") thick strip or plank flooring to plywood laid on a slab, ensure to use a 1 1/2" cleat, not the usual 2" cleat due to its' length being too long. In all other applications the 2" cleat is preferred.
.03 Installation of Hardwood Plank Flooring:
  • Hardwood plank flooring laid on plywood-on-slab, on screeds, and plywood or board sub-floors shall be installed in strict accordance with hardwood flooring manufacturer's recommendations and NFCA minimum requirements.
  • Plank flooring is installed in the same manner as strip flooring. Planks may be installed using the same width throughout or by alternating courses by widths, starting with narrowest boards, then the next width, etc., and repeating the pattern.
  • Manufacturers' instructions for fastening plank flooring vary. The general practice is to blind nail flooring members through the tongue as with conventional strip flooring, using one or more (depending on width of the plank) countersunk screw or nail fasteners at each end of each plank and at intervals along the plank to hold it securely in place. Nails shall be countersunk and puttied and screws shall be covered with wood plugs glued into the holes. Alternately adhesive may be applied for 100 mm (4") or wider width planks to avoid using nails or screws. Care should be taken not to use too many screws and plugs which will tend to give the flooring a "polka-dot" appearance.
  • Some manufacturers recommend face nailing in addition to other fastenings. Another practice sometimes recommended is to leave a slight crack, about the thickness of a putty knife, between planks. The Design Authority should consult the flooring manufacturer's installation instructions for details.

.04 Installation of Parquet, Block, Herringbone, and Similar Hardwood Flooring:
Note: This section applies only to tongue-and-groove parquet flooring where tongues and grooves are engaged and does not apply to slat-type or finger block parquet.
  • The styles and types of block and parquet flooring as well as the recommended procedures for application vary somewhat among the different flooring manufacturers. Detailed installation instructions are usually provided with the flooring, or are available from the flooring manufacturer or distributor. The Design Authority should consult the hardwood flooring manufacturer or supplier for such information.
  • Blocks and the individual pieces of parquetry should be laid in adhesive or mastic over a wood subfloor, or over a moisture barrier on a concrete slab as previously described.
  • Adhesive and mastic coverage rates and trowel size must be as recommended by the manufacturer. Some mastics must be allowed to set overnight or up to 48 hours in accordance with manufacturer's directions. Most wood floor adhesives and mastics, regardless of type or open time, will allow the parquet tiles to slip or skid when sidewise pressure is applied for some time after open time has elapsed. By working from "knee boards" or plywood panels laid on top of installed area of flooring this sidewise pressure is avoided. For the same reason no heavy furniture or activity should be allowed on the finished floor for about 24 hours.
Note: Some hardwood flooring must be rolled after installation to ensure 100% full contact or bonding with the adhesive / mastic. This requirement must be verified with the adhesive / mastic and hardwood flooring manufacturers. Refer also to 2.04 above for additional requirements.

  • There are a number of ways to layout parquet flooring. The most common is with the edges of parquet units (and thus the lines they form) square with the walls of the room. Another way is a diagonal pattern, with lines at a 45° angle to walls.
  • Each piece must be carefully aligned with all of its neighbours. Small variations in size, natural to wood, must be accommodated during installation to keep overall pattern squared up. A "creeping" pattern cannot be corrected after it develops; the more carefully laid out floor causes fewer problems during field work.
  • Wood parquet must always be installed in a pyramid, or stair-step sequence rather than in rows. This again prevents the small inaccuracies of size in all wood from magnifying, or "creeping" to gain an appearance of misalignment.
  • Blocks or parquetry pieces should be cut to fit all walls and an expansion space allowed on all sides. Cork or polystyrene blocking should be installed between flooring edge and wall to permit the flooring to expand and contract.
  • With blocks, a diagonal pattern is recommend in corridors and in rooms where the length is more than 1-1/2 times the width. This diagonal placement minimizes expansion under high humidity conditions.
.05 Installation of Ornamental Hardwood Flooring Elements:
  • Where ornamental elements such as borders and fields, insets, inlays, medallions, and mixed media are to be installed, such elements shall be installed in strict accordance with NOFMA "Ornamental Floor Design and Installation" requirements using the most appropriate methods noted therein for the type of elements and flooring system that apply.
  • In all such cases accurate measurement, layout, and finishing requirements are critical.
.06 Installation of Strip Block Flooring:
  • Strip block flooring can be installed over clean and acceptable concrete or plywood substrate surfaces using adhesives as noted herein.
  • Strips are installed in a parallel pattern in accordance with the manufacturer's directions and flat tapped into the mastic.
  • Increased resilience can be achieved by installing 13 mm (1/2") or thicker corkboard between block flooring and the substrate surface in accordance with manufacturer's recommendations.
  • Expansion gaps at walls and other vertical surfaces must be provided in accordance with requirements noted herein. Temporary plywood or lumber strips are placed in void and replaced with cork expansion strips at intervals within void.
.07 Installation of Hardwood Sports Flooring:
Most hardwood sports floors, including gymnasium, handball, squash, and racquet ball court floors use Northern Hard Maple strip flooring.
  • There are a variety of installation methods used for installing hardwood sport flooring. In each case the type (width and thickness) of flooring and installation of the particular system must be in strict accordance with flooring manufacturer's directions. In addition, the Design Authority should consult with the hardwood sports flooring manufacturers or suppliers for local availability of such systems.
  • As most hardwood sports flooring systems are proprietary the following general information includes most system assemblies:
    • Panel System: this system utilizes resilient pads attached to the underside of two layers of laminated plywood with the flooring nailed to plywood.
    • Sleeper System: this system utilizes resilient pads attached to the underside of pressure treated wood sleepers with the flooring nailed directly to the sleepers.
    • Sleeper/Panel System: this system utilizes resilient pads attached to the underside of pressure treated wood sleepers with one or two layers of plywood nailed to sleepers, and the flooring nailed to the plywood.
    • Direct Glue-Down System: This system utilizes specially formulated elastomeric adhesive and low profile 8mm (5/16") or 18mm (11/16") hardwood flooring.
  • Other special proprietary resilient installation systems are also available including:
    • Metal Channel and clip systems using heavy-duty flooring anchored at each channel with lock-in clips.
    • Metal channel and high density plywood nailing strip system using 26mm (33/32") flooring
    • Resilient steel leaf spring and solid blocking (sleepers) and plywood sub-floor system using 26mm (33/32") flooring.
  •  Game Equipment Floor Inserts: Floor sockets for game equipment such as volleyball, tennis and badminton net posts are typically provided with the sports flooring. The installation details vary with the type of (wood or concrete) floor system installed and must be carefully coordinated with various trades before the installation of flooring commences.
.08 Special Hardwood Installation Systems:

  • Plank flooring can be installed using a clip system method. Various proprietary systems specially designed for wood flooring, are available from hardwood flooring manufacturers. The Design Authority should check with flooring manufacturer or supplier for availability and details of such systems.
  • For added resilience and greater sound abatement a sheet of acoustical underlayment (as noted in Part D03C - Material Guide - Flooring) can be placed directly on the substrate below the flooring. Such material is supplied by the hardwood flooring supplier.
.09 Changing nailing direction
  • Prepare slip tongue inserts.
  • Once the row of flooring to receive the direction change is chosen, insert wood glue into the groove followed by a slip tongue (spline) in the exposed groove.
  • Always glue and nail the slip tongue in place.
5 • INSTALLATION PROBLEMS

.01 Crowning and Cupping:

  • Kiln dried hardwood flooring subjected to gaining or losing moisture on one side faster than on the other will result in the flooring expanding on the moist side and warping away from the moisture. Refer to the following details in regard to cupped and crowned floors:
  • Cupping: When the underside of hardwood flooring absorbs moisture cupping will occur and the surface of boards will be concave or "U" shaped (i.e., the outer long edges will be higher than the centre of the boards). If unchecked, heavy expansion may ensue, followed by buckling of the floor. Often, however, only enough moisture is present to cause the cupping, and this will be the extent of damage. Rapid cupping may also occur when an impervious surface finish is applied, cutting off evaporation through the surface and resulting in an accumulation of moisture on the underside of the flooring. It may also occur when flooring is installed over damp substrate sheathing or where there is no moisture barrier between the flooring and the substrate surface.

  • If cupped boards are dried soon enough, they usually return to a flat position. However, if they remain cupped long, the stresses within boards may change to the extent that drying will not remove the cupping. This is more common in wider boards.
    Replacing a cupped floor is usually the worst choice, especially if replacement is made before the moisture condition causing the problem has been corrected. Replacement flooring is almost certain to react to the moisture situation by cupping, like the first floor, and the whole process must be repeated.

    Some cupping should be considered normal, especially in 125 mm (5") and wider planks and particularly in plain-sawn boards. In such boards (as opposed to quarter-sawn) the growth rings of the tree travel in a slightly curved pattern from one side of the board to the other. This curved pattern produces, with normal moisture content changes, a slight convex or concave cup, depending on how the rings curve within individual boards. This type of cupping is usually not noticeable unless the floor is viewed across the boards and against a strong, low light source, such as through a large window or patio door and is more noticeable if the space is empty.
  • Crowning: When the topside of hardwood flooring absorbs moisture due to excessive humidity crowning will occur, and the surface of the boards will be convex or crowned, i.e., the centre of the boards will be higher than the long edges. Crowning will also occur if the flooring is sanded when the board are cupped and the high edges cut flat by the sanding machine. After sanding, the boards will then have abnormally thin edges, i.e., flat on top with edges of the reverse side of boards still curved upward, or cupped.

  • If these boards later dry and flatten to their original position, the thin edges recede, leaving the top of boards convex (edges lower than the centres) and the back again flat against the subfloor.
  • Repair: The first step in repairing a cupped floor is to remove the source of moisture, which entails finding its source.

  • In crawl-space or concrete slab substrates ensure that outside drainage (drain tile) moves water away from the inside slab or area.

  • In crawl-space construction ensure that a vapour retarder membrane (e.g. 1.5 mm (6 mil) polyethylene film) is installed over the ground surface and that the crawl space area is properly ventilated and that there is some method of limiting ingress of moisture-laden air.

  • In basement construction the perimeter drainage and under slab vapour retarder must be reviewed to ensure that they are "working". In addition or where necessary provide mechanical dehumidifiers and summertime ventilation as required to ease the problem enough to allow the subfloor and surface hardwood to dry.

  • Once the moisture source has been eliminated or controlled, the floor and all under floor construction must be allowed to dry thoroughly, a process that may take a number of weeks or even months. The drying process must be monitored by taking moisture readings on a bi-weekly or monthly basis, and no repairs should be attempted until the readings have remained balanced between face and back of the flooring for 30 days to be sure that cupped floors have flattened as far as they are going to. Note that floors with a surface finish will react much more slowly to moisture changes.

  • If the floors remained cupped after thoroughly drying it has most likely set new stresses and most boards will remain cupped indefinitely. In this case the only practical repair is complete re-sanding and re-finishing. Cracks should be filled as a normal part of the finishing process and fastenings checked and repaired before sanding.
.02 Panellizing:
  • Shrinkage of hardwood flooring strips and planks in dry seasons is normal and generally results in the formation of hairline gaps beside each individual piece. Panellizing is an un-natural shrinkage behaviour pattern of installed strip or plank flooring that can develop during the first or even subsequent heating seasons and is caused by flooring boards losing moisture to a drier interior environment and shrinking in groups. The groups of strips or "panels" may contain any number of pieces within this "panel" that are "stuck" tight together. This transfers the aggregate shrinkage, or total shrinkage for all the pieces in the panel, into large gaps between strips on either side of the "panel" with the gaps being very noticeable and objectionable. No manufacturing or kiln drying procedure (nor lack of one) during production of the flooring itself can produce this phenomenon.
 
  • Panellizing, the result of external forces acting on a hardwood floor that tug, push, and lock the strips of flooring together, is caused by a number problems:
    • Foundation settlement: Perimeter foundation settlement can cause a floor joist structure to stretch across centre supporting beams resulting in gaps between floor surfaces. If the settlement is extreme, the floor joists will raise near the centre beam. This "jack-knife" effect will cause humps to form in the floor. In a strictly technical sense, this effect is not "Panellizing" but just large abnormal gaps.). Hardwood flooring gaps or "panels" caused by foundation settlement usually occur near the centre beam, and often are limited to one or two major cracks. They can occur elsewhere, however, particularly when plywood is the subfloor, in which case the panels will follow the seams of the plywood subfloor.
    • Floor finish edge bonding: Although the process is not fully understood, apparently some types of surface finish such as polyurethane seep between individual flooring strips and planks resulting in bonding between some of them and "panel edges" or "panellizing". Floor finishers must ensure that they employ the total system specified by the finish manufacturer as skipping a required sealer coat may at times contribute to panellizing.
    • Subfloor movement: Subfloor material often must remain exposed to the elements for days or weeks while the building is under construction and will absorb excess moisture from exposure to rain or high humidity. When the roof, windows and doors are in place and the building is closed in, this material will begin to lose the moisture as soon as the environment becomes drier. When this occurs every wood component with high moisture content, i.e. subfloor sheathing, joists, and beams, will shrink and move. This shrinkage and/or shifts caused by framing movement that occurs after the installation of flooring can result in gaps between flooring components and may appear in any sort of random pattern and may result in "panellizing".  Panellizing is most often caused, in the case of subfloor shrinkage, by movement of the subfloor plywood sheathing. Plywood has been shown to retain fasteners well and as both the plywood and hardwood flooring dry, the plywood tends to pull flooring strips along panel edges in the opposite direction. This sometimes produces a "panel" effect in hardwood flooring with separations roughly corresponding to edges of plywood panels. This is most likely to occur along the long dimension of plywood panels parallel to the direction of flooring strips.
.03 Repair: in order to repair panellizing it is necessary to either repair the gaps and/or remove the panel sections. A number of options are available and any one or all may be required on the same floor. Some of these options are:
  • Filling of gaps: By far the simplest method is to fill panel gaps if they are less than 2 mm (3/32") with a colour matched wood floor filler. This must be done when the moisture content of the flooring is at its median stage, i.e., halfway between its highest and lowest seasonal readings (typically in late spring or fall in four-season areas). The filler should be sealed with a similar finish that is on the floor or the entire floor may need screening and coating where more extensive filling is required.

  • As the flooring will expand with moisture gain and shrink with loss of moisture every year, the cracks should be filled when the gap is large enough so that the filler will not be squeezed out as the floor shrinks in wet seasons and large enough to leave the smallest possible crack when the floor expands in dry seasons. For gaps wider than 2 mm (3/32") the filler may be squeezed out as the flooring expands in humid seasons, or the filler itself may break leaving a jagged-edged gap when loose chunks of filler are vacuumed away. If there are many gaps 2 mm (3/32") or wider in small areas more extensive repairs may be necessary.

    If only gap filling is necessary, and if the floor has a polyurethane coating or seal-and-wax finish, the finish can normally be repaired very simply after the filler is well dried. The floor must be first buffed with a No. 120 or finer screen and thoroughly vacuum cleaned. The floor is then recoated with one coat of polyurethane. For seal-and-wax finish apply sealer to filled areas then re-wax with coloured wax to match the original finish.

    White-finished floors offer some potential problems due to the nature of the pigmented colouring, and where it lies within the finish. The above technique can be tried, and if results are unsatisfactory, full refinishing may be required.

    • Selective removal and replacement of boards: Where large "panellized" cracks occur near a wall or other vertical interfaces, those boards nearest the interface can sometimes be removed and reinstalled to eliminate the gap. Where possible, the boards should be replaced in the same sequence as they were removed. This will allow simpler finish repairs.

    • If boards are replaced with new, un-sanded material, it will probably be necessary to re-sand and re-finish the entire floor.
.4 Caution: The remedy often demanded by unhappy owners, is to remove and replace panelized floors with new flooring material. However, if the cause has not been cured then panelizing will occur in any new flooring.
In all cases, repairs should be performed by an experienced floor finisher whose judgement should be relied on to provide the proper remedy for each circumstance. Experience is the best teacher in deciding which gaps will hold filler, which need adjacent boards to be reinstalled, or wider boards custom fit to replace cracks, and how best to match the filler to the surface.
.03 Ledging (Lippage)
  • Adjacent flooring pieces should be, within reason, even across their seam. Product milling issues, sub-floor issues and or incorrect installation can lead to unevenness referred to as ledging between neighboring pieces of flooring.
    • Engineered
      • For a select grade of engineered hardwood flooring a tolerance of .31mm (.012") is acceptable. A character (rustic) grade of engineered flooring is 0.63mm (.024") is acceptable.
    • Solid
      • For solid wood flooring, milling tolerances vary between manufacturers. There is no one written standard for ledging tolerance for solid wood flooring. A general guide would be that ledging should not exceed .5mm (.017") at time of installation for planks less than 3 1/4" in width. The wider the plank the more likely natural movement will cause this issue and that the ledging will exceed the norm.
      • Wood floors shrink, expand and move through the four season cycle hence some ledging is to be expected.
6 • SITE FINISHING OF HARDWOOD FLOORING

.01 Refer to Part D04D – Installation Guide - Finishing for site and factory finishing of hardwood flooring.