Is treated or untreated plywood more acoustically dead?

Vapor barrier over pressure treated plywood for hardwood floor over

• Our customer wants to install an unfinished, thin, hardwood floor over pressure treated plywood. The moisture difference between the two materials needs to be within 2% to 4%. The plywood tests at almost 20%, the hardwood between 4-6%. We need a vapor barrier that will close up around the nails. One material suggested is "bitchathane" but the flooring contractor checked with the manufacturer of one type used by roofing contractors in "ice" situations. The manufacturer didn't think it would work but thought there might be another product that would, but needed the list of materials in the pressure treated lumber. What should we use to fix this problem? We are already using fans to try to dry out the plywood but it will undoubtedly take a very long time to dry out enough. We think the vapor barrier will be the answer...

• Answer:

  Hi carter9, Thanks for your very well-presented question. You obviously are dedicated to finding the best solution for your customer, and I believe I have come up with it. W.R. Grace & Co. makes a product called Perm-A-Barrier System 4000 Wall Membrane that seems to satisfy all your requirements. I chased your problem around the Internet for a couple of days, then found myself in conversation with the support people at Grace. They assure me this product will do the job for you, and my experience with their company's Construction Products Division gives me confidence in their expertise although they obviously have an ax to grind in answering your question. Perm-A-Barrier is described on their website as "a tough, self-adhering, self-healing composite membrane. It consists of 0.9 mm (.036 in) of rubberized asphalt and an integrally bonded 0.1mm (.004 in), high density cross laminated polyethylene film. When combined with a structural substrate, Perm-A-Barrier wall membrane produces a virtually impermeable air and water barrier on concrete, masonry, gypsum board and wood walls. It is designed to be a cost-effective system which acts as both an air and vapor barrier. Perm-A-Barrier Wall Membrane retards the diffusion of moisture through the building enclosure. It provides a continuous seal against air and vapor leakage around the entire building." The product is sold as a vapor barrier for vertical surfaces, but I am assured it will work well in your application as well. Here are its most salient features: 1) virtually impermeable to moisture 2) cross-laminated film for dimensional stability and tear, puncture, and impact resistance 3) cold-applied, so no flame hazard 4) self-adhesive 5) flexible to accommodate minor settling and shrinkage 6) self-healing around mechanical fasteners (one of your main concerns) 7) comes in 3' x 83.4' rolls, each weighing about 75 lbs. If you go to this page, you will find a thorough data sheet detailing topics such as handling, safety, application, and so on: http://www.na.graceconstruction.com/vaporret/download/permem.pdf W.R. Grace representatives for your part of the country are: North (Area Codes 209, 341, 408, 415, 510, 530, 559, 650, 707, 831, 916, 925) Scott Tyson Florprufe, Perm-A-Barrier, Procor 866-333-3726, select option 3, then option 2, extension 5675 [email protected] Bob Ogletree Florprufe, Perm-A-Barrier, Procor 866-333-3726, select option 3, then option 2, extension 5670 [email protected] The W.R. Grace office nearest to San Mateo is just across the Bay from you at: 2140 Davis St San Leandro, CA 94577-2292 Phone (510)568-3427 Again, I think the solution above will very nicely do the trick, and Grace, as you probably know, is a reputable company with an extensive network of support representatives and distribution points. If you have any concerns about this answer, just ask for clarification and I'll be happy to get right back to you. Thanks again for your question, and best of success with your project. Regards, ericynot-ga