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RH in Concrete for Wood Floor with Vapor Membrane
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06-14-2012, 10:31 AM #1
eaadams Concrete Moisture Expert *****
Status: Offline Posts:591 Threads:85 Joined:Jul 2010
I am looking for advise on establishing a RH for a wood floor system. (special system from Europe very dimensionally stable)

The flooring has a RH limit of 90% over 6-mil poly that has a perm of 0.06.

I want to put the flooring down over 15-mil poly with a perm of 0.018-0.01. (83% less)

What RH should the concrete be? perhaps 83% of the difference between 90 & 100? So that would be 98% rH? I don't think it is a sliding linear scale though.

06-14-2012, 10:51 AM #2
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
Here's my take:

The poly won't matter if a failure occurs. They will test the slab and if it is above 90% you are screwed.

The better poly will do a better job of keeping MVE from the wood. But concrete that is very high in rH has a multitude of issues beyond moisture vapor. If moisture vapor was the problem, we'd have had it licked long ago!

Realistically though, yes a better poly will do wonders for you, although it may be a warranty battle, you probably will never have an issue. There are products better than poly available if you want stronger and tighter vapor retarders also....

But you know all this! Wink

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

06-14-2012, 10:56 AM #3
eaadams Concrete Moisture Expert *****
Status: Offline Posts:591 Threads:85 Joined:Jul 2010
Yea I'm considering Stego so ... a little better than poly. Perm of 0.01

06-14-2012, 10:59 AM #4
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
Stego is tough too!

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

06-14-2012, 12:20 PM #5
eaadams Concrete Moisture Expert *****
Status: Offline Posts:591 Threads:85 Joined:Jul 2010
Good point, I don't want it degrading over time. I wonder what is a more harsh enviroment, in between concrete, or under a floating moving floor.

06-14-2012, 05:56 PM #6
CCR Concrete Moisture Coach ***
Status: Offline Posts:236 Threads:14 Joined:Dec 2011
Poly sheet is risky with wood is what I've always heard. How much is a roll of the dice. For my money, I'd want Koester or Ardex MC with a 15 year warranty under my wood floor.

JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com

06-15-2012, 07:01 AM #7
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
Yes, for about $1.50/sf you could eliminate any question at all..... Wink

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

06-18-2012, 04:55 PM #8
Rubensgt40 Concrete Moisture Coach ***
Status: Offline Posts:172 Threads:13 Joined:Oct 2011
I attended a wood flooring job where a slab took moisture from a plumbing failure. There was poly sheeting on the slab, 12mm ply then 13mm overlay solid timber. The whole thing buckled like buggery. So there are definitely points which poly cannot withstand. As JD always advises- see what the warranty says!

The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


06-18-2012, 05:55 PM #9
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
Seems maybe the seams were open, or the plastic failed or something.

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

06-19-2012, 11:49 AM #10
eaadams Concrete Moisture Expert *****
Status: Offline Posts:591 Threads:85 Joined:Jul 2010
1) Yes we would all like Koster or Ardex under the floor but at $4.50 sf it isn't cost effective.
2) If there was a plumbing leak the existing wood floor would have fallen apart. Also a plumbing leak defeat any Koster or Ardex anyway. I had one job where the bleacher guys drilled into a water pipe when mounting the bleachers to the wall. The floor was saved thanks to a great superintendent on the job who took car jacks and jacked up the entire wood floor system 5', ran fans and dehumidifiers all night. Cost them a pretty penny for the fix (~1/4 of the floor had to be replaced) but it wasn't a total loss.

When it comes to Warranties, if you have to go to the Warranty you are screwed anyway. I was talking to my REEF rep (0.22 s/f) and was discussing the perm tests with him. He discounted the perm ratings. However his product is fiber re-inforced which might work better under a floor for wear and tear over time. The Stego (0.20 s/f) rep pushes the perm tests but discounted any abrasion over time.

Still though, no one has provided me any guidance as to my original question as to how to select an RH guide. Just a lot of talk. Just like Calcium Chloride is used as a 'well it should be about X pounds' I am getting the feeling the way people come up with RH guide numbers is not based in any science or logic.








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