Question on vapor barrier attachment

[bob_mp]

Greetings,

I am getting ready to pour the slab for my new shop. It's an 8" slab on top of 15 mil Stegowrap.

The concrete contractors were planning on tucking the vapor barrier under the felt expansion joint which is nailed to the stem wall. I talked to the Stegowrap guys and that suggested placing the vapor barrier between the slab and the expansion joint.

Please see the attached image.

The concern I have about tucking the vapor barrier under the felt is that in some places, there are voids in the fill right below the felt, This would seem to be placing concrete against the stem walls without any expansion joint at all. If the slab were to move/expand, there would be nowhere for it to go without hitting the wall.

Now placing the vapor barrier on the inside (away from the stem wall) of the felt solves this problem but creates another. The felt does not seem to stick to any of the tapes I have tried. I have about a half a dozen adhesives I will try tomorrow, but I'm not sanguine.

The nail in the felt is also worrisome. If the vapor barrier is under the felt, the concrete is directly in contact with the nail. It seems like potentially a whole lot of force concentrated on the nail. Something to worry about?

I would appreciate some guidance.

Thanks,
Bob

 

[OldTC]

I wouldn't think it would make any difference at all.

I'd cut it so it laid flat on the fill and not turn it up at all....but that's me.

Did you say an eight inch slab??? My.

 

[willymakeit]

Install vapor up the wall,install expansion on top of vapor. The concerns are minute.
If you are still concerned use a peel strip on top of the expansion. After the concrete has set ,remove the peel strip and caulk with a urethane caulk such as Sonneborne or equal.

 

[ConCretin]

I prefer locating the vapor barrier behind the expansion material. It doesn't make any difference with regard to the vapor barrier - it simply easier to secure for the reasons you mention.

Don't sweat a little concrete to concrete contact under the expansion material or the nails holding the expansion material. Concrete expansion is negligible and not a problem. Contraction i.e. crack control is a far bigger issue.

 

[OldTC]

I'm glad you said that LLWillysfan,.....if a guy is pouring a garage or shop floor where the temperature change inside is relatively minimal, especially if you're pouring in decent weather,...there is really not much need for expansion joint.

I've been in construction and remodel all my life and I've never seen a floor move a stem wall. Contrary to popular belief; that oil impregnated expansion joint will not crush due to the it's large surface area. Besides,...the slab under expansion is pushing on the heads of the concrete nails, (used to attach the expansion joint), which are transferring that "push" to the stem wall,...after all; they are not driving further into to concrete.

 

[Dick in Wisconsin]

Is the slab going to be thick enough?