- 1). Ensure the concrete slab is thoroughly dry and the moisture content is below 80 percent before installing the flooring. To test for moisture content, tape a 6 mm thick plastic sheet to the concrete floor. Completely seal the edges of the plastic. Overlap any seams by at least 6 inches and tape them also. After 72 hours, take a reading with a dew point hygrometer. The moisture content should be below 80 percent and there should be no damp odors, discoloration or dampness under the plastic.
- 2). Level the surface of the slab by adjusting the surface of the concrete, if necessary. Remove any high spots and fill in any low spots. Use a grinder to sand down any high spots and concrete patching compound to raise any low spots.
- 3). Clean the concrete slab thoroughly, using a mixture of trisodium phosphate (TSP) and water, following the manufacturer's mixing instructions. Use a sponge or string mop to apply the solution and then rinse well with clear water. Allow it to dry for 48 hours before proceeding.
- 4). Install a plastic vapor barrier over the concrete. Use 6 mm polyethelene plastic sheeting. Lay the sheeting over the floor, extending the sheeting beneath the baseboards on the perimeter. Overlap the edges of the plastic by 4 to 6 inches.
- 5). Put down 4-by-8-feet sheets of 1/2- to 3/4-inch plywood on top of the plastic sheeting. Cover the entire floor with the plywood panels but leave a 3/4-inch space between the edges of the panels and the baseboards at the perimeter of the room. Also leave 1/4 inch between the plywood panels. These small gaps are necessary to allow the wood to expand and contract.
- 6). Attach the plywood to the concrete slab with concrete screws. Space the screws every 16 inches in all directions.
- 7). Install the hardwood flooring boards using the plywood as the nailing base.
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