Concrete Contractors & Perimeter Insulation

Rod Kotiga

What about landscapers and insulation under the pavers for snowmelt. Yikes !

Rod

Heatman_2

Concrete Contractors & Perimeter Insulation

What is with concrete guys and our perimeter insulation. Has anyone learned how to deal with stubborn concrete guys who do not like our 2" foam insulation around the perimeter of the basement slab. Had a concrete guy today refuse to pour the slab with perimeter insulation installed. Whats your thoughts?

singh

Tell me about it !!

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Rob Blair

My cousin is building and I offered him all the materials, plus help to install and no payments until he could do it!

Contractor told him he would not guarantee the slab or foundation if we put in the heat!

He needs to do some reading to increase his customer base!

Rob

hot_rod

What do you mean by perimeter?

are you just installing around the outside slab areas?

Some concrete finishers feel having some foam and the rest gravel changes the cure and causes a crack line at that point. I don't have proof of that but it does give them and excuse. Insulating under the entire slab may be a better choice for response time and lowest possible operating cost.

What type of guarantee does it negate? Only two things you can guarantee about concrete.... It's going to crack and nobody will steal it!

hr
hrand ns

Glen

It's going to crack and nobody will steal it!

Definitive statement! One concrete contractor went so far as to inform the HO that the concrete will "crumble into pieces" if radiant tubing was installed. Education is still essential. Despite his best arguments - the tubing was installed - 10 years ago - and it is of course still intact.

Rob Blair

I guess now I can say that there are three things that you can guarantee with concrete! I always was told it will get "HARD" and it will "CRACK"! Now I can add the third.

Rob

hot_rod

If you don't want it to crack

leave it in the bag, was another "old timers" comment.

hr

Rick Kelly_4

Masons

Using past experience with masons, I would go over what had to be done, and then wait for the objections. If there was any lip, I'd say "No problem if you can't comply with the specs. I had someone else lined up who has plenty of past experience with these installations but they were a bit busy. I just need to give them a call and they will come through for me. Thanks for coming out to look at the job.". Some would walk away but most would give it their best. Once they knew that they weren't going to be calling the shots it would become obvious that they could take the job or leave it for someone else.

ScottRW

Hot Rod

My concrete guy explained it to me like this: When you pour over Insulation, the moisture has nowhere to go but up, drying out the slab in a much faster time frame, which will of course increase the risk of not only more cracking, but larger cracks. Conversly, when pouring over pea gravel, the moisture tends to stay in the concrete and allows the slab to cure at a slower rate. Slower rate= less cracking and smaller ones to boot. I have found that if I pour on a cloudy, not too hot day, late in the Fall or early Spring, I get pretty good results. Good luck finding those parameters. Hope this helps. Scott

Metro Man

Concrete Compliant Contractors

What we do is have the GC set all the insulation. Spell out in contract that insulation is to be used and that concrete contractor is responsible for that pour. We will miter the top edges on the perimeter if it's going to be an issue with concrete contractor and we are ALWAYS there for the pour.

Even after all of that........ there are still issues. I try to find concrete guy b4 pour to re-remind them what will be required. If they're complaining I tell them that they should just add into there bid.

We used some reinforced light-weight concrete on a pour b4, let sit like the old timer told us to for min. 3 weeks. He said it may spider crack (never did) then the tile guys where good to go. Worked out great and we poured down to 1-1/2" in some spots.

Cool concrete truck. Mixed cement, gravel, and water on site. You just payed for what you used.

HR.... I'm stealing your "going to crack an no-one will steal" statement.

Metro Man

ALH_4

Curing a Slab

Unless I am not following your concrete guy's logic correctly, moisture should leave the slab more slowly if it can only go one direction. There are many ways to control moisture when curing a slab, and generally the slab should be kept continuously moist for a minimum of 7 days. On a separate note that comes up frequently, ACI also has rules for loading of insulated slabs, which I believe are typically 1/5 of the compressive strength of the insulation for live load and 1/3 for dead load. Dow has foam with compressive strengths of 25psi, 40psi, 60psi, and 100psi. 25psi foam should far exceed any loading typically seen in a residential application.

Rob Blair

I am glad you jumped on that one Andrew. I think that he got it backwards.

Rob

eluv8

insulation under concrete

If the contractor is familiar with pouring on a vapor barrier, he can pour on insulation. Its the same... some bring up that it may compress. If you go to the manufacture of your product you can get the compression data and ratings for under concrete. I got my specs from Dow Chemical who makes the blueboard variety of XPS. I also know Owens Corning makes the pink stuff but I am unaware of their current ratings. If they are worried about the hairline NON-STRUCTURAL but unsightly fractures that sometimes occure due to uneven curing of the concrete and excess moisture off the top. I have used a 1"-2" layer of sand on top of the foam with very good results, and has become my preferred method of installation. I also design for a 6" slab thickness to account for the extra mass. Fear of the unknown is sometimes hard to deal with. Hopefully they are open to education. Hope this helps. The 2 jobs I did without full insulation are the only jobs I look back on as not my best work. Keep trying in the long run the future homeowners will appreciate your work after the concrete guy is long gone.

Tom Manton

What a load

Pouring over and within insulation is done probably thousands of times a day. If you don't like a little extra bleed water use the sand over insulation method, we just deal with it, it's no big deal and less work to deal with the bleed water then the sand.

Another old timer saying, there's only two kinds of concrete, cracked concrete and concrete that's going to crack. It's the sub-base that determines if the crack is a hairline or displaced, a displaced crack means improper prep of the sub-base. If you can't deal with hairline cracks then you need to place control joints.

Heatman_2

We use 2" high-density foam for underslab and perimeter insulation, always have hairline cracks around perimeter, but usually there is a framed wall covering this void. Any suggestions that can make everyone get along better?

Kevin O. Pulver

I'll remember you forever HR

It's just kinda sad that of all you've said,
that's the thing I'll never forget!
Kevin

Kevin O. Pulver

Roweston I somewhat agree

but for different reasons.
It appears to me that the concrete is slower to start setting up- because as you say the water stays in an comes to the top rather than draining through the gravel.
Then, when it finally starts to set- it sets faster, because the insulation is holding the heat in rather than the ground acting as a heat sink. So the guys kinda have to wait around... and then HURRY! Nevertheless, it's in the best interest of the homeowner to have radiant. What's easy is of no concern to us contractors. And you're right about the cloudy days to help with a slow cure. I've even seen that happen... Once for sure. Kevin