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knifer 01-19-2009 09:17 AM

need help with mastic type
 
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.

angus242 01-19-2009 09:20 AM

Are you planning on laying tile?

knifer 01-19-2009 09:23 AM

Quote:

Originally Posted by angus242 (Post 215495)
Are you planning on laying tile?

No, I am planning to nail 3/4 hardwood to 3/4 ply as subloor. That's why I need mastic-like waterproofing so when nail goes through it mastic will seal it well.

angus242 01-19-2009 09:35 AM

Quote:

Originally Posted by knifer (Post 215496)
No, I am planning to nail 3/4 hardwood to 3/4 ply as subloor. That's why I need mastic-like waterproofing so when nail goes through it mastic will seal it well.

Mastic and waterproof are 2 terms that do not go together. Mastic (as an organic adhesive) will re-emulsify when becoming wet.
I am not familiar with a product that does what you're looking for. I'm sure a wood flooring installer will chime in shortly.

jaros bros. 01-19-2009 09:39 AM

You will probably end up going to a flooring store to find it. Too much of a specialty intem for the box stores to carry, especially for DIYers.

Josh Jaros (Jaros Bros. Construction)

knifer 01-19-2009 09:40 AM

Quote:

Originally Posted by angus242 (Post 215501)
Mastic and waterproof are 2 terms that do not go together. Mastic (as an organic adhesive) will re-emulsify when becoming wet.
I am not familiar with a product that does what you're looking for. I'm sure a wood flooring installer will chime in shortly.

I got all my info from NOFMA hardwood install quide:
Quote:


With
34" plywood used as a nailing base, the recommended
vapor retarders are affixed to the slab. These
systems may be either 2 membrane asphalt felt/building
paper and mastic or a 4-6 mil polyethylene film or an

equivalent system as described below.
....
Two membrane asphalt felt or building paper system.
Prime and apply cold cut-back asphalt mastic
with a notched trowel at the rate of 50 sq. ft per gallon.
Let set 2 hours. Roll out 15 lb. asphalt felt/building
paper, lapping edges 4". Butt ends. Over this apply a
second similar coating of mastic and roll out a second
layer of asphalt felt/building paper. Lay both layers
of felt in the same direction, but stagger the overlaps
to achieve a more even thickness.

As I understand simple 6mil ply is way easier but this two membrane method is more moisture proof. Thanks.

HardwoodGuy 01-19-2009 12:43 PM

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/har...onconcrete.htm

knifer 01-19-2009 01:23 PM

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.


Quote:

Originally Posted by HardwoodGuy (Post 215612)
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/har...onconcrete.htm



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