Hello, <!—-><!—-> <!—->
I sure can use some help. I’m planning on installing a hardwood floor over an above grade (~2′) concrete slab. The concrete slab was poured over a year ago. The concrete slab is in an addition off my kitchen which has a 3/4″ existing oak hardwood floor. The cement slab is ~2-1/2″ below the top of the hardwood floor off the kitchen. If I just install one sheet of 3/4″ plywood over the slab I’ll have a transition at the threshold of the room. I talked to several contractors about the best way to install the 3/4″ plywood subfloor in the addition and got just as many ideas from gluing and nailing to just gluing (construction adhesive). The most recent contractor suggested that perhaps I install two 3/4″ sheets of plywood over the slab nailing the plywood together and letting the subfloor float over the slab with the 3/4″ oak floor installed over this. This would still leave only ~1/4″ difference between the two floors. Using two sheets of plywood is ok with me as it allows me to get the two floor near level. <!—-> <!—->
Do I need a vapor barrier between the cement and the plywood? Is any method of installing the subfloor preferred over the other?<!—-> <!—->
I’d appreciate all the help I can get as I plan on installing the subfloor myself. <!—-><!—->
<!—->Thanks <!—->
Replies
You are installing a hardwood floor over an exsiting hardwood floor? Why?
WHen work gets slow I work part time for a hardwood flooring installer, we did 5,000 sq ft of flooting floor for the YMCA. over the cement we laid down one layer of the cheapest cdx plywood he could find, then laid down a second layer running the other way, so the seams were perpendicular. Then we put in the hardwood floor. The only nails holding it all togeather were from the installation of the hardwood.
I wouldn't put down a vapor barrier it will trap moisture and cause mold.
Thanks for the reply.
I am installing a hardwood floor over a cement slab in a room adjacent to a room with an existing hardwood floor. The slab is ~2-1/2" below the top of the existing hardwood floor in the adjacent floor.
You suggest not using a vapor barrier because of mold. Wouldn’t the purpose of the vapor barrier be to keep the moisture between the cement and the vapor barrier preventing and mold from getting to the wood?
I’m not opposed from this technique it’s just a question. Also, wouldn’t it be better to nail the two plywood sheet together?
Thanks again for the reply.
Mark
Mark, Correct, don’t use a vapor barrier, it will trap the moisture between the cement and the plastic and cause mold there. Some moisture in you wood is good, I don’t know the percentages. Around here (MN & ND) lack of moisture in the winter is more of a problem then to much in the summer. We didn’t specifically screw or nail our plywood together on the YMCA job, but in the process of nailing the hardwood to the sub-floor (the two layers of plywood) it all got nailed together.
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Here is another idea from Fine Home Builder, lay down a layer of expanded- polystyrene, and then two layers of plywood then screw it to the cement. The article is on page 79 of March 2005 issue # 169. It is an article about a dry, mold free basement.
I installed bamboo directly to an on grade concrete floor that was poured about 1978. I glued it down with Bostic's best, which pretty much becomes your water barrier. You can play basketball on that floor. It is 2 years old now and as solid as if it grew there.
Look at Bostic's site.