HARDWOOD FLOORING INSTALLATION GUIDE
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Plywood-On-Slab Method
This system uses ¾" or thicker sheathing grade exterior plywood as the subfloor over the appropriate vapor retarder. Loose
lay ¾" plywood panels over entire floor. Laying plywood on a diagonal to the direction of the finished floor will help prevent cracks associated
with panel edges.
Stagger plywood and joints every 4' by cutting the first sheet of every other run in half. Leave ¾" space at all wall lines and ¼" to
½" between panels. Cut plywood to fit within 1/8" near and around door jambs and other obstructions where finish trim will not be used.
Fasten the plywood with a powder-actuated concrete nailer or hammer-driven concrete nails. To be sure to flatten out the plywood, start at the center
of the panel and work toward the edges. Use at least nine nails per panel or more to fasten securely.
An alternate method is to glue the ¾" plywood over the vapor retarder systems which include the cut-back mastic. Cut the ¾" plywood into
4' x 4' squares or 16" x 8' planks, score the back 3/8" deep on a 12" x 12" grid, and lay panels in the cut-back mastic applied with a ¼" x ¼"
notched trowel (35 sq. ft. per gal.). Remember to stagger panel joints by 2 ft.
Screeds System
This system uses as a nailing base flat, dry 2" x 4" screeds of Group1 density wood (sometimes called sleepers) of random lengths from 18"
to 48", as a nailing base. They must be preservative treated with a product suitable for interior installation. After treatment screeds must be dried to a
Moisture Content of 12% or less, if saturation with water is involved.
Screeds are laid on their flat face in rivers of mastic with screeds run 12" on center at right angles to the direction of the finished floor.
Sweep the slab clean, prime with an* asphalt primer and allow to dry. Apply hot (poured) or cold (cut-back) asphalt
mastic and imbed the screeds. Stagger joints and lap ends at least 4" and leave ½" space between lapped edges. Be sure there is enough mastic for
100% contact between screeds and slab. Leave ¾" space between ends of screeds and walls with a continuous run of screeds at end walls.
Over the screeds lay a 4- to 6-mil polyethylene vapor retarder with edges lapped over rows of screeds. Avoid bunching or puncturing it, especially between
screeds. The finish flooring will be nailed to the screeds through the film
The system with screeds spaced 12" on center and a moisture retarder without a subfloor is satisfactory for all ¾" Strip Flooring and Plank Flooring
less than 4' wide. Plank Flooring 4' and wider requires either the Plywood-On-Slab subfloor, or screeds plus a wood subfloor, to provide an adequate nailing
surface. The subfloor over screeds may be 5/8" or thicker plywood, 3/4" OSB (performance rated), or 3/4" Group 1 dense softwood boards or equivalent no wider
than 6". If subfloor boards are used over sleepers or screeds, allow ½" spacing between boards.
Installation Over Wood Joist Construction
Outside cross ventilation in the foundation walls must be provided through vents or other openings with no dead air areas. A surface cover
throughout the crawl space (100%) of 6 mil polyethylene film is essential as a moisture barrier.
Subflooring. With ¾" thick strip flooring use either kiln-dried boards of NO. 1 or NO. 2 Common Pine or other dense, Group 1 softwoods
suitable for subfloors over wood joists, or exterior sheathing grade plywood. If plywood, 5/8" (19/32") or 3/4" (23/32") performance rated products are
preferred. Also, 3/4" (23/32") OSB is a comparable substrate. With 1/2" thick strip flooring use a 3/4" (23/32") subfloor.
Thinner materials cannot be recommended as a preferred subfloor material.
For a board subfloor, use only flat, dry 3/4" dressed square edge boards no wider than 6". Lay diagonally across the joists; allow 1/4" to 3/8" expansion space
between boards. Don't use tongue and groove boards. Nail every bearing point (includes blocking) with two 8d common nails. All mitered joints must rest on joists.
Mark location of joists so flooring can be nailed into them.
Good nailing is important. It keeps the boards rigid, preventing creeping sometimes caused by shrinkage in subfloor lumber. Without adequate nailing it is impossible
to obtain solid, non-squeaking floors.
| * - Always follow manufacturer's instructions |
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