4 mil vapor Barrier versus 6 mil ??


Converting 300 sq ft garage into family room. Installing full floor above garage concrete slab. I want to put a polyethylene vapor barrier on the concrete.
Most places I read recommend 6 mil polyethylene. Home Depot selling for $50.
When cleaning out the garage I found a brand new box of 4 mil polyethylene that my Dad had given me.
Would it be a problem if I used the 4 mil that I have, instead of buying 6 mil?
I have a giant box. Can I double-up the 4 mil, creating a 8 mil barrier?
Thanks,
Chris
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might be ok if all seams sealed and overlapped. but plastic isnt forever. how old is it?
if your getting a permit run it by the local code enforcement building inspector
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Prob Ok if never exposed to sunlight! But 300sq ft. of 6 mil not very expensive? Assuming you have to insulate and vapour barrier the walls (unless they are already insulated and vapour barriered) use the 4 mil for that? Also what about the ceiling insulation and vapour barrier for a room that will now be heated, occupied by living breathing people and other activities that put out moisture; is that insulated and vapour barriered?
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On Sat, 20 Sep 2008 16:49:31 -0700 (PDT), wrldruler

Hi Chris,
Polyethylene is an extraordinary VB.
(I won't bore you with the details, but I use .1 mil for certain purposes, and it does the job.)
So, in your situation, the issue is fragility rather than the thickness needed to provide a barrier to the migration of moisture.
I would say "yes," you could use the 4 mil (and be careful to avoid tearing it.) Or, double it, and sleep a bit better.
All the best,
--
Kenneth

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