Asphalt covered styrofoam
 

Have a line on 4inch thick 2ft X 4ft high density blue styrofoam (probably roofmate) price is about $3 per pc ($12 per full sheet) Canadian or $9.60 us. Thirty cents US per sq ft.
It was used on a roof and covered both sides with hot tar.
I want to use it to insulate under a 2 inch floor slab with hydronic heat tubes.
The construct will be something like
water proof membrane,
1 or 2 inches of styrocrete,on grade, at about 1 cement 2 sand 6 or 8 ground up styrofoam by volume.
4 inches of tar covered styrofoam
piping and sand to just cover the pex heat pipe
2" normal cement possibly with mesh.
for a normal house hold floor.
My concern is with the tar, over the years it does not seem to have harmed the foam, but will the tar/oils be able to migrate upwards through the concrete?
Your thoughts would be appreciated.

Note to add;
Have done quite a bit with "styro crete" at the mix above, with good results.
Have found that by putting down a couple of inches of wet styrocrete, then placing the foam with a back and forth motion the foam is very well supported I can walk on 2 inch thick styrofoam with no cracking once the styrocrete is 24 hrs cured.

Curious why you would want to cover the PEX with dry sand? Compared to concrete, dry sand is not such a good conductor of heat.

Look it up in the Engineers Handbook

-AC_Hacker

Thanks AC, had not thought of the heat transfer. Sand was suggested by a fellow from Alberta, where it gets really cold, his opinion was that the sand allowed some movement in the Pex as it heated and cooled, he had done a few churches that way. Seemed like a good idea & with 4" of foam under, I suspect the heat transfer losses would not be significant.

"Thanks AC, had not thought of the heat transfer."

You are about to spend a lot of money and time working on a project that is specifically about thermal transfer, that you will live with for many years, and you have not thought about thermal transfer?

There is a problem here.

It looks like you did not look at the information I gave you. So I will make it easy... look at this:

From this source:
What is thermal conductivity for sand
Thermal Conductivity (W/m K) of
>Coarse SAND (dry) is 0.25 (W/m K)
>Medium SAND (dry) is 0.27 (W/m K)
>Fine SAND (dry) is 0.15 (W/m K)

From this source:
http://www.orbee.org/images/5cc-reso...-materials.pdf
Thermal Conductivity of concrete = 1.28 (W/m K)

This means that on average, concrete is almost 6 times better than dry sand at conducting heat.

In the long run it means that if you use sand, you will be paying more money to heat your house, every year, as long as you live there.

It is your floor, it is your money, it is your project.

-AC_Hacker

Thanks again AC, my Marks is buried deep under construction materials right now.
It will be two years before we pour the floors, so have not bothered to do the math yet. The sand idea was put forth over a few beer on the beach in Mexico, so not to worry.
Am more concerned right now with the asphalt covered styrofoam, if we decide to use it, I need to get it soon, so was hoping for feedback on that.
Or ways to ensure the asphalt oils do not migrate (capillary action) upwards

Boy no opinions on using the tar covered insulation below the slab on grade floor.
Still wondering if the oils from the tar might migrate upwards through the cement.
Or what material, plastic?, would control it. It sure is a lot of insulation for not much money.

Highly unlikely the tar will go anywhere unless it gets pretty hot, as in above boiling point of water. Over the centuries, it may extrude out the sides, but again highly unlikely within your lifetime...especially considering the compressibility of the styrofoam.