I'm building a 3000 sq ft ICF ranch house over a full basement and would like to use a GSHP for a radiant floor heat system. For the first floor, the most economical solution seems to be a 1-1/2" lightweight concrete slab on top of a (suitably engineered) wood subfloor. I would like to then stain some of the concrete and use it as a finished floor in some areas. My problem is that the concrete guys I've talked to here in southwest Ohio look at me like I'm crazy. I've read in these forums that others have had success with this type of design, but the concrete guys are very concerned about the slab cracking. Any advice or resources you could point us to would be very appreciated. Thanks.

hello,
1 1/2 concrete will crack. big time. you can mitigate with a couple things, place plastic on top of the platform before you attach pipe and you will need a control joint pattern. A pattern on 2 or 4 foot centers (cuts of 1/4-3/8 inch next day after pour), this does not look bad, you will still have cracks.
To minimize cracks you really are limited to a thicker topping, think 2 1/2 even that will crack, you will want to add to the joist system and still need control joint cuts of of corners that extend in to the room and something on a 10x10 or 12x12 pattern. Also think about a 7 1/2 sack mix/pea gravel on the mud, and adding fiber mesh to tie it together. Fiber mesh will leave small bumps on finish slab. The finished concrete is an affordable option though and you can place an acid wash on top for a finished floor.
Good luck,
Dan

If you are doing ICF, why not just use Insuldeck or similar so you have the concrete slab built in? You will get a full-density efficient radiator floor that way.

We sell a lot of concrete with our radiant floors and snow/ice melting systems here in St.Paul MN. For thin slabs we use expanded wire over the properly supported sub-floor. You have to have a structural engineer approve a 2" thin-slab over a sealed deck. There are people out there that know how to do it...mostly commercial applicators.

In my own applications and with other regular designs the second floor can be heated from below the sub-floor (nearly all of my retrofit radiant floor designs) and in new construction we use sub-floor radiant and in a recent SIP home in the Minneapolis area we installed radiant ceilings allowing for a variety of floor coverings without the added labor of a sub-floor system or weight of a "wet" radiant floor such as concrete or Gypcrete®.

Design water temperature for the SIP home radiant ceiling is just over body temperature and for my own 1921 farm house about 110°F.

Comfort without compromise.

We did a 1.5" stained concrete over a wood deck(with radiant).

We put down plastic sheeting before pouring, beefed up the joists and put in more of them. We have cracks. They are all where hallways meet doorways or larger rooms. Not all doorways, but where bigger slabs meet larger slabs. If we were to do it again( and we will) control joints or decorative wood transitions would be placed in those areas.

We love our floors.

j has it right. Crack control is critical. If tile is to be applied on top of same the old wire and mud method or a crack control barrier should be applied. The good folks at Maxxon® know all about this as Gypcrete® and other cementious materials act like concrete without the weight.

We have used both with great results but some experience is helpful.

I like the solid feel, sound and fireproofing and as mentioned the free-hand application of PEX tubing to the sub-floor laying out more intuitive patterns for perfect radiant comfort. But like radiant floor itself, nothing good is free.

Thank you all for your help.
-Insuldeck would be a great option, but unfortunately, it is out of my price range.

-I will investigate some of the crack control methods you described. I like the idea of using decorative wood strips at the doorways.

-I'm a little worried about cutting control joints on 2 or 4 foot centers. I would hate to nick any of the PEX tubes. I guess you'd just have to make sure you only went 1/4 inch deep with the saw.

Thanks again for your input

-Insuldeck would be a great option, but unfortunately, it is out of my price range.

Really? What did you get quoted for it? My sense is that it is pretty competitive.

Did you compare subfloor framing + cost of over pour + insulation costs to the Insul-Deck cost?

Keep in mind that using Insul-Deck can help with the engineering of your ICF walls as well.

Whats the going rate for gypsum cement in the US? I have over 1 million feet of tubing installed in the last 25 years, 40% of which is in gypsum and while there are some minor cracks (and those are due to floor movement) I stiill have only a few where the gypsum is the finished floor. We used epoxy coating for it.

About $4.00US. Is all that tube PB?

Posted By Elvis on 05 Jun 2012 02:15 PM
Thank you all for your help.
-Insuldeck would be a great option, but unfortunately, it is out of my price range.

It's about $15 a square foot, which includes the InsulDeck form, rebar, cement and labor.

Posted By MikeSolar on 05 Jun 2012 06:18 PM
Whats the going rate for gypsum cement in the US? I have over 1 million feet of tubing installed in the last 25 years, 40% of which is in gypsum and while there are some minor cracks (and those are due to floor movement) I stiill have only a few where the gypsum is the finished floor. We used epoxy coating for it.

Is this the same as "Gyp creek"?

I've seen the self leveling gypsum cement used in commercial hotels and years later the stuff cracks and creeks. It is one of the nosiest floors I have ever seen. Hence the term it has earned, "gyp creek".

Posted By BadgerBoilerMN on 05 Jun 2012 11:35 PM
About $4.00US. Is all that tube PB?

Only my first job was PB, never again. I went to Wirsbo right after that and i could buy directly from the distributor and pick from the shelves.

They decided to distribute through a national wholesaler who knew nothing about the product and always had an important  part missing from stock, just when you really needed it. Then i left to go to Rehau and have been very happy since.

$4/ft is about right here as well for gypsum. Wish it were less but when you see the equipment they need to have, I don't blame them.

Posted By Lbear on 06 Jun 2012 02:30 AM

Posted By MikeSolar on 05 Jun 2012 06:18 PM
Whats the going rate for gypsum cement in the US? I have over 1 million feet of tubing installed in the last 25 years, 40% of which is in gypsum and while there are some minor cracks (and those are due to floor movement) I stiill have only a few where the gypsum is the finished floor. We used epoxy coating for it.

Is this the same as "Gyp creek"?

I've seen the self leveling gypsum cement used in commercial hotels and years later the stuff cracks and creeks. It is one of the nosiest floors I have ever seen. Hence the term it has earned, "gyp creek".

The gypsum cement (if you listen to the adherents) products have a cell wall that expands when wet so it has some flexibility. I seldom see cracks or hear noise. I think you must be thinking of some air entrained product because gypsum (Gypcrete is just one brand, Hacker is another) is well known as a sound deadener and fire separation.

As we all know concrete shrinks so the cracks will come, hairline maybe, but still there.

Are you guys suggesting the OP uses Gypcrete instead of concrete? He wants to stain the concrete, not something you can do with gypcrete.

With the right engineered mix and fibers, one can get 1.5" concrete that is flexible, as strong as 4" and doesn't shrink or expand (pre-cure to post-cure). But I'd take a closer look at aluminum plates and then tile.

The gypsum cement (if you listen to the adherents) products have a cell wall that expands when wet so it has some flexibility.

I'm trying to figure out how gypsum cement has "cell walls".

Posted By ICFHybrid on 08 Jun 2012 08:23 AM

The gypsum cement (if you listen to the adherents) products have a cell wall that expands when wet so it has some flexibility.

I'm trying to figure out how gypsum cement has "cell walls".

Like anything it is not a homogeneous mass and maybe cell wall is not the right term but the 3 manufacturers I spoke with way back all used the same term. Again, according to the manufacturers at the time, the "particle" swells when wet and holds the shape once the moisture has been removed so it has a capability to except some movement without cracking. I have seen this happen many times with gypsum but you won't see it with concrete which shrinks, as we all know.

I did work with one of the manufacturers many years ago to find a coating that could be stained but it was a royal pain and I don't know how it fared in the long run.