When a shallow footing is done (18" deep) for a slab on grade design. Can the footing and ICF stem wall be done at one time or must the footing be done first, cured, and then the ICF stem wall form placed on top of the footing?

The problem with the latter is that you have TWO cold joints. The footing top and the ICF stem wall top.

Either approach is acceptable. When we only have short stem walls, we find it preferable to accomplish both the footing and the short stem walls in one pour. We typically don't use ICF for interior stem walls. When we have tall ICF walls, we pour the footing first. The footing has dowels and a keyway formed using 2x4s. Then we subsequently pour the ICF walls. The dowels and keyway make the cold joint a non-issue.

Another thing I am noticing is that some contractors DO NOT like pouring a slab on grade on top of rigid foam. Most of them complain about it and claim that the concrete will not cure correctly due to the foam beneath it. They claim concrete needs to cure both ways (top & bottom) but on footings concrete is not curing from the bottom because it's facing soil that is not getting oxygen to it.

ICF which has foam on both sides cures completely fine, actually, it cures really strong because it cures slowly and doesn't dry out as fast.

What is it with these contractors and not liking rigid foam underneath the slab?

It's amusing to see someone who justifies his prowess in the field by his number of posts [size matters] show such complete ignorance about the basics. When has a cold joint at the footing or a slab on grade ever been an issue? All concrete walls have a "cold joint" at the footing unless the footing is poured at the same time - which is the exception by far. Your contractors obviously know that you know nothing about concrete or building and so feel free to tell you anything no matter how far fetched - like foam underneath won't let it cure. LOL. While these are perfectly legitimate questions for a newbie or DIYer who knows almost nothing about concrete or building, they do not even warrant a response to someone who has claimed to know so much - except one from sailaway, likely out of pity. A more humble approach that is in line with your level of experience is called for.

Posted By mojoe on 23 Sep 2016 12:09 AM

I never said I agreed with the concrete contractors statements. If you actually read my post I disagreed with his statement about curing since ICF cures within an EPS sandwich perfectly fine.

Cold joints are inevitable but the less of them, the better.
 

Don't get your hostility? "Size matters" ?

No need to personally attack people and turn the posts into a trolling session for internet trolls.

It's not hostility or a personal attack, it's a statement of fact. You previously dismissed my comments and asserted your own - posing as an expert in the field and justified it by your sizable post count in spite of the fact that you were mistaken. Did you arrive at that posting total by asking thousands of questions like those? Don't get me wrong. I don't mind how many silly questions you ask. Just don't pose as an expert when you don't even know the basics and obviously have no real experience in the field. I hope you aren't charging anyone - that would be a travesty.

You are correct Lbear, the EPS only delays the cure which can result in a stronger slab. EPS is commonly used as under-slab insulation...and so is vapor barrier... Depending on how you finish the floor, you might want to place the vapor barrier either above or below the EPS. Placing the vapor barrier below the EPS can result in water being trapped between the vapor barrier and the EPS during the pour which can cause moisture to be slowly released over a longer period of time. This can be mitigated by taping the EPS seams or using an interlocking EPS under-slab insulation system like Nudura HydroFoam.

Posted By sailawayrb on 23 Sep 2016 03:50 PM
You are correct Lbear, the EPS only delays the cure which can result in a stronger slab. EPS is commonly used as under-slab insulation...and so is vapor barrier... Depending on how you finish the floor, you might want to place the vapor barrier either above or below the EPS. Placing the vapor barrier below the EPS can result in water being trapped between the vapor barrier and the EPS during the pour which can cause moisture to be slowly released over a longer period of time. This can be mitigated by taping the EPS seams or using an interlocking EPS under-slab insulation system like Nudura HydroFoam.

In dry climates do you still recommend slab vapor barriers?

This is a typical buildup:

4" compacted AB material
3" Rigid Foam
4" reinforced concrete slab

I think a vapor barrier is generally a good idea for an insulated interior slab. You could put it under the foam or tape the seams of the foam which will achieve the same basic result of limiting the long term transfer of moisture from below the insulation into the living space. The barrier under the foam has the added benefit of allowing the insulation to ultimately reach the same moisture content as the slab.

We typically do whatever depth of 3/4 minus is required to achieve the required building top-of-slab design elevation. Then we build the footings on top of the 3/4 minus. Then we fill the interior area up to the footing height with self compacting pea gravel. Then we place vapor barrier on top of the pea gravel (assuming we will use stamped or polished concrete for the floor finish). Then we place high density EPS insulation (either 2 or 4" thick depending on the required minimum R-value ) on top of the vapor barrier. Then we pour the concrete slab (either 4 or 5" thick depending on whether it contains HR tube).

Has anyone used 10ml or 15ml Stego Wrap for VP/water barrier underslab? I saw a sample at a builders conference last week in Charlotte. Bright yellow and seems to be stronger than any 10ml plastic I have ever used. I looked it up and found A.H.Harris has it for $350 for 14' x 140', cheaper than anyone else. I don't have any affiliation with Stego or Harris. Rich M

Posted By sailawayrb on 22 Sep 2016 12:27 PM
Either approach is acceptable. When we only have short stem walls, we find it preferable to accomplish both the footing and the short stem walls in one pour. We typically don't use ICF for interior stem walls. When we have tall ICF walls, we pour the footing first. The footing has dowels and a keyway formed using 2x4s. Then we subsequently pour the ICF walls. The dowels and keyway make the cold joint a non-issue.

Do you typically charge more to do an ICF stem walls than with the ICF house walls?

No, we charge the same amount per square foot. We charge less for an interior stem wall that we just form using plywood.

No, we charge the same amount per square foot. We charge less for an interior stem wall that we just form using plywood.

@ Lbear,

Have you looked into FASTFOOT ? you would have no cold joint on your footing.