Recent advances in technology have
made hardwood floors in underground (below grade) basements a safe and
reliable option. All concrete floors emit water vapor, and basements in
particular are notorious for damp conditions and water seepage
through the slab. However, as long as proper precautions are taken and the
appropriate products used, you can still have a hardwood floor in your basement
that is fully covered by the manufacturer's warranty.
In the case of my latest
installation, this involved a number of steps which I've outlined below.
Hopefully this information will help other homeowners in evaluating the
potential of their basements for hardwood flooring.
Preparation
A chat with the homeowners, and a
quick inspection after a record rainfall, revealed no evident problems with
water seepage through the floor. The basement was clean and mold-free. A
hygrometer measurement indicated moderately high levels of humidity
compared to the rest of the house--about 70%. The homeowners purchased a
dehumidifier and a hygrometer to address this issue. Within hours the humidity
had dropped to 50%, which is a nice median percentage. Maintained year-round,
the floor should experience minimal swelling or shrinking.
The concrete floor underneath the carpet had been polished
and treated with an epoxy or oil finish. Using a diamond-blade grinder
attachment on a buffer, I removed the coating and achieved a light surface
texture. These steps ensured maximum adhesion when it came time to glue down
the wood floor.
 |
| original surface |
 |
| prepared for adhesive |
With a clean substrate, it was time to measure the vapor
emissions from the concrete, using two calcium chloride tests from Taylor
Tools. I placed a dish containing a
known weight of calcium chloride on the concrete floor, enclosed it under a
plastic dome that sealed tightly to the concrete, and waited 65 hours.
Then,
with the help of a friendly pharmacist, I had the dishes re-weighed, calculated
the increased weight, and ran the figures through the formula provided by the
manufacturer. The test indicated that emissions were just a hair over 5 pounds
of water per 1000 square feet per 24 hours--fairly dry conditions that,
especially in light of the excessive rainfall this summer, indicated no major
concerns with the concrete slab.
Products
For extra security, and to allow
room for possible increase in moisture emissions down the road, we used Bona's
R851 adhesive, which is warranted to protect wood floors up to 12 pounds of
vapor emission. Since our slab was right around 5 pounds, the hardwood floors
should be amply protected. The calcium chloride test results were independently
verified by a lab, giving both Old Town Wood Floors and the homeowner proof
that the adhesive warranty conditions were complied with.
As a second precaution, this time to
guard against possible elevated humidity in the future, we used Owens Plankfloor engineered wood instead of the typical solid oak. With
multiple layers of hardwood plies glued perpendicularly to each other, the
danger of humidity-related swelling or shrinking is significantly reduced.
Engineered wood can remain stable under more extreme moisture changes than
solid wood. The best feature of the Owens Plankfloor products, however, is that
on top of the engineered foundation, each board has a 4.5mm thickness of solid,
unfinished oak. Thus we were able to match the floors in this house both above
and below grade, using the same grade of red oak, and employed identical
sanding and finishing techniques for a flawless match across all three stories
of this house. And just like the rest of the house, the basement floors can be
refinished multiple times down the road.
