Could foam lines show up in concrete?

[bfarroo]

I've been talking with a few different contractors the past two weeks to get quotes on buildings and site prep. One mentioned that his concrete guy said the vapor barrier should go over the foam to keep the concrete from seeping down between the cracks between the sheets and leaving lines in the finish. I've never heard anyone do it that way and I told him that typically the vapor barrier goes down then the foam on top. Have any of you heard of this happening? maybe the mix was to thin? I know I've seen some people tape the foam together which I may consider if it could be an issue. Also is there any value to putting the foil type insulation in the areas where the lift will go? I'm thinking not but figured I'd ask. Have any of you had issues with the foam wanting to blow away after it gets put down before the tubing gets installed and the rebar gets set?

Thanks for the help guys,

 

[stingry]

I've been talking with a few different contractors the past two weeks to get quotes on buildings and site prep. One mentioned that his concrete guy said the vapor barrier should go over the foam to keep the concrete from seeping down between the cracks between the sheets and leaving lines in the finish. I've never heard anyone do it that way and I told him that typically the vapor barrier goes down then the foam on top. Have any of you heard of this happening? maybe the mix was to thin? I know I've seen some people tape the foam together which I may consider if it could be an issue. Also is there any value to putting the foil type insulation in the areas where the lift will go? I'm thinking not but figured I'd ask. Have any of you had issues with the foam wanting to blow away after it gets put down before the tubing gets installed and the rebar gets set?

Thanks for the help guys,

NO
NO Foil is basically worthless for underslab insulation. I put XPS under the whole floor, including under the lift.
and NO

Cheers
Steve

 

[wssix99]

The foam should be sealed with special tape:

This article from the Portland Cement Association gives the info on where to place the barrier: http://www.cement.org/tech/cct_con_vapor_retarders.asp

 

[bfarroo]

They don't show using insulation in the article though. Where do you get the tape from? I'd prefer not to tape it just because of the size of the building but will if there is a chance of the concrete sagging.

 

[classic boost]

i didn't tape my foam in my 40x32. no lines showed. i can't see how they would anyways.

 

[Highbeam]

No reason to tape the foam when you have a poly vapor barrier beneath.

 

[brownbagg]

the vapor barrier always goes against the concrete, the form board be under the vapor barrier

 

[TheBadDog]

Wow, talk about a lack of consensus...

 

[Rookie2]

"what does it matter !"

 

[NUTTSGT]

If the contractor thinks lines are going to show up from the foam joints with 4" of concrete on top, I would not be using him.

 

[wssix99]

They don't show using insulation in the article though. Where do you get the tape from? I'd prefer not to tape it just because of the size of the building but will if there is a chance of the concrete sagging.

The article is all about engineering the vapor and slab, but even that (not to mention location of the insulation) is debatable and regularly debated by experts and the concrete trade associations. The problem is trade-offs between trapping water in the concrete, (and seeing more cracking from differential shrinkage) constructability, and longevity of the insulation.

The tape is available from any commercial building supply that sells the foam.

i didn't tape my foam in my 40x32. no lines showed. i can't see how they would anyways.

I'd think that if there is a pathway in some areas for moisture to get away from the concrete, it could influence how shrinkage cracks propagate and the slab curls. Likewise - I can't figure out how this would create lines on the surface.

the vapor barrier always goes against the concrete, the form board be under the vapor barrier

PCA recommends (in the article above) in some cases putting the barrier under the sub base to improve quality of the concrete and reduce curling. A lot of it depends on the environment the slab is in.

 

[cyamaha2007]

When we had to meet a specific grade of precast concrete decking for over basements and stuff we had to tape the seams of the foam. It was so the thin mud couldnt seep between the **** join of the foam. It was for structural reasons due to making a imperfection creating a stress point. This may not be what your contractor is talking about but I taped the seams on my xps for vapor barrier reasons. If the foam is taped its a vb all on its own. Since the standard plastic vb can deteriorate over time its just a back up. I would put the xps under the lift its fine in this application. Im not a engineer but do know a great deal about concrete unfortunately.

 

[Quijote]

Is an epoxy finish considered a "moisture-sensitive finish?" I may well epoxy my yet-to -be built garage, so I am curious if I should request a vapor barrier beneath the slab.

 

[Kevin C]

the vapor barrier always goes against the concrete, the form board be under the vapor barrier

DOW says to put the vapor barrier under the foam.

 

[Kevin C]

Is an epoxy finish considered a "moisture-sensitive finish?" I may well epoxy my yet-to -be built garage, so I am curious if I should request a vapor barrier beneath the slab.

Epoxy does not like back pressure from moisture. Regardless, of floor finish, you should put in a vapor barrier. Last I checked its a code requirement, even for a garage.

 

[wssix99]

Is an epoxy finish considered a "moisture-sensitive finish?" I may well epoxy my yet-to -be built garage, so I am curious if I should request a vapor barrier beneath the slab.

No, its not moisture sensitive. After talking to my contractors, I think we are going to go with the barrier above the sub base and under the foam, even though its in a protected and conditioned space. We figured that the barrier would hold up better long term in that location vs. being sandwiched between two rough surfaces.

PCA recommends putting the barrier lower for some slabs to allow more moisture to escape from the slab as it cures. This is probably more critical for industrial slabs that have curling concerns.

 

[srmofo]

Plastic Is Cheap. Put It In Both Areas If It Concerns You