1. Plywood sub-floor
- For nail down installations (engineered or solid wood) use STD Douglas Fir plywood
- Minimum plywood thickness should be 5/8”
- We don't recommend OSB (oriented strand board) for nail-down installations because we don't believe it provides the same holding power as plywood.
2. Sub-floor 'flatness'
- Should be 3mm + or – over 10’ (concrete or plywood)
- Level the plywood sub-floor by sanding off high spots and building up low spots with layers
of 1/8" or 3/8" thick plywood as necessary. Glue and nail, or staple the extra layers of plywood
For concrete sub-floors
- Grind down high spots and use cement leveling compound to fill in low areas. Use best quality
cementitious leveling compounds with an acrylic additive for flooring that is to be glued down.
Less expensive self leveling products can be used for floating floors.
3. Sub-floor moisture
- The maximum moisture content in the plywood sub-floor should be 12%. The difference in moisture content between the plywood and the hardwood should be no more than 4%.
- Concrete moisture content should be no more than 3lbs of vapor emissions per 1000sqft. Use a Calcium Chloride test (ASTM F1869) or RH test (ASTM F2170) to confirm this.
- Installing solid wood flooring over a crawl space or car port or garage risks excessive shrinkage and expansion.
- Always use a moisture barrier when installing wood flooring on concrete which is at or below ground level.
4. Site Conditions
- Never acclimate the wood flooring on site without confirming the sub-floor is dry, the space is heated to 20c, and the relative humidity is between 40% and 60%.
- Ensure the space to receive the hardwood flooring is at lock-up stage (protected from the outside elements) and has the main heat on before delivering the flooring to site.
5. Hardwood flooring moisture content
- Should be approximately 8%.
6. For nail down installation
- Nail or staple the hardwood every 6” to 8” when installing over plywood.
7. Reducing squeaks/tighten the sub-floor
- Re-screw old sub-floors with 2” or 3” decking screws before installing the hardwood flooring.
8. Relative humidity in the house
- Should be between 40 and 60% before the wood flooring is delivered.
9. House temperature
- Should be at 20c before wood flooring is delivered.
10. Trades using water in their product (i.e. tile and drywall)
- Work must be completed before the hardwood flooring can be shipped to site.
All of this information and more can be found in the National Floor Covering Association's 'Floor Covering Reference Manual' - a fantastic source of information for floor covering installations. You can buy this manual on line at http://www.mfcsi.com/reference-manual.html
Note: ALWAYS read the installation guidelines or instructions that come with the product you have purchased. Those instructions should supersede any instructions given above. Avoid purchasing your flooring from an auction because of potential milling, moisture content and warranty issues. Hardwood flooring problems are expensive to fix (if they can be corrected at all), choose a product and installation firm that has a good reputation and offers a real warranty.