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need help with mastic type

7K views 7 replies 4 participants last post by  knifer 
#1 ·
What type of mastic am I supposed to use for layered moisture barrier for hardwood nailed to ply over concrete?
It's supposed to be something called "cold cut back asphalt mastic" but I could not finad anything like that in my local HD/Lowes/Menards. Thanks.
 
#7 ·
Interesting this question is asked. Having installed solid hardwoods over concrete for a good number of years in South Florida I can only think of one job that used the older mastic method and that was back in the early 90's.

I would guess try a roofer...really. I have no idea where to find it. For years the procedure I saw used was laying 6 mil visqueen plus #15 asphalt felt paper then attach the plywood with concrete fasteners(tapcons, hilti, aerosmith, concrete cut nails).

Many will argue the above procedure punctures the moisture barrier. True. But in all my years I never encountered a problem. Another idea is a floating subfloor. While using the same visqueen(6-8 mil plastic) and #15 felt, install two layers of 3/8" plywood in opposite directions and over lapped. Attach with a staple gun. Plywood costs increase but you don't get into that very messy mastic situation.

I'm also kind of curious why I never hear the use of Bostiks MVP used as a substitute to the mastic. Simply spread as you go, lay the ply in place then attach. It would solve the seal being broken angle when attaching in my opinion.

Don't neglect floor preparation before.

Some more insight...

http://www.hardwoodinstaller.com/hardwoodinstaller/hardwoodonconcrete.htm
 
#8 ·
I was told that "punctuated 6 mil poly" is ok if you 100% sure concrete is not going to get moist. Like for houses that located on artificial hill where basement is half exposed. But too risky for old houses on gound level where noone knows what waterproofing was done for foundation and what is located below slab.

For MVP I believe the only way to go is either floting subfloor or MVP+glue without subfloor. With just one level of MVP it's not going to seal nail holes and for multiple levels it's just too pricy (like $1 per sq ft per level)

Thanks.
 
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