Installing Hardwood Flooring

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Clear the Decks

Actually putting the floor in place involves a lot more than nailing boards down. Preparation will prove, over time, to be more important than layout. In a structure with floor joists, renail any loose pieces and vacuum the subfloor clean. If the surface has uneven spots (check by rolling a marble across its length and breadth), you may need to level it with 1/4" underlayment; use ring-shank nails and lay the seams perpendicular to those of the plywood.

Then cover the entire area with 15- or 30-lb. builder's felt, overlapped about 6" at the seams (Fig. 4). The paper works to block moisture and subdue squeaks, so don't try to get by without it. Concrete floors must be topped with a wooden subfloor to nail into, and there are two ways of providing it. The first calls for a base of 3/4" squareedge exterior plywood laid over a glued vapor barrier. Clean the slab with a primer and apply an even layer of cold asphalt mastic, using a notched trowel. The adhesive should be cut to cover about 50 square feet per gallon, and be sure to allow for plenty of ventilation while you're working. After about two hours, roll out one layer of builder's felt, edges overlapped, then trowel another coat of mastic on top of this.

Cover the area with a second layer of felt, placing the seams so they fall between the others. You can also use one 6-mil polyethylene layer and eliminate the second covering, but you may have to slit out bubbles which form under the plastic. When that's done, lay down your plywood so the joints are staggered; it's easy to do if you halve the first sheet of every other course.

Leave a 1/4" space between panels and 3/4" along walls, then fasten the wood down securely with 2 1/2" concrete nails. If you can rent a shot nailer—a powder-actuated fastener that runs about $18 a day plus 25¢ a cartridge—it's well worth the extra expense. You'll need to use nine to 12 nails per panel to anchor the floor properly. The other method uses 2 X 4 nailing strips as sleepers—false joists which are glued to the concrete.

These "screeds" range in length from 18" to 48" and are treated to resist decay. Use an asphalt primer on the concrete, then trowel 1/4"-thick rows of cut mastic onto the surface, centered 12" apart, and arranged perpendicular to the direction the finished floor will run. Lay the strips into the adhesive, alternately side-lapping the joints at least 1/4", and allow a 3/4" expansion space at the walls. When all the screeds are in place, you can spread a 6-mil poly vapor barrier over the surface, allowing the edges to lap where there's a screed row (Fig. 5).

The finished floor is nailed directly to the wood, unless the flooring is made of planks wider than 4"—which would need a 5/8" or thicker plywood subfloor as an anchoring surface. If preparation is the hardest part, then ordering your flooring may seem the most confusing. It isn't, really, if you understand that flooring is often sold by the board foot as well as the square foot. Board-foot measurement represents the volume of lumber it took to make the finished piece, and is always greater than the amount of wood you're actually getting, because a portion has been removed in the milling process.

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