Boiler radiant heat on second floor

DesignerDiana

Our firm has a request from a customer to have her entire first floor to be radiant heat through a boiler system. This is a new home with a full basement. We've done radiant heat with a boiler before but typically have used gypcrete and then a finished floor (tile/wood/etc) as our final layers over that. Problem here is she wants to keep the concrete floors and have them polished. Excuse my ignorance, but isn't that going to be too tough to do? Concrete doesn't self level well. Gypcrete is super leveling, but we can't leave that exposed or it'll flake off, we'd need actual concrete as the top layer. What's the best system/layers to do this in? Do we need to insulate the joists below as well for heat retention? That was brought up to us but we've not done that before. Looking for some good expert tips here. Thanks.

Ironman

The only solution that I see would be to have the floor reinforced to where it could sustain the load of the concrete. Either that, or your client accepts a more reasonable solution.

And yes, you should insulate under the floor.

hot_rod

It is almost impossible to keep a thin 1-1/2” concrete pour from cracking. Be sure to let them know that

Assuming the floor  joist are beefy enough to hold the weigh?

 Base trim need to come off, doors trimmed up the  pour thickness, and any stairs will have a tall first step that will not be very easy to negotiate 

A thin overpour really needs to be considered earlier in the process 

DesignerDiana

We haven't built the home yet so any weight can be accounted for when we order floor trusses and steel basement beams. If 1 1/2" thick of concrete is too thin, what is the preferred pour depth?

Daveinscranton

If the home is not built yet, why not consider an ICF floor?.  Lay the ICF, following the instructions, add oxygen barrier pex, pour the concrete.   Done.  Insulation is built in.  Incredibly strong.  Ideally, stone floor or ceramic tile over the ICF.  I suppose you could do polished granite etc but it might be slippery.  

No floor trusses.  No subfloor.  No floor joists.  Figure out your layout and escapes for wiring etc early.  Incredibly strong.  Cost effective too.  

ICF walls while you are at it.  At least for the basement.  Goes fast.  Easy too.

Brace the ICF floor well for the pour.  Or hire someone who has done more than one.  

jesmed1

DesignerDiana said:

We haven't built the home yet so any weight can be accounted for when we order floor trusses and steel basement beams. If 1 1/2" thick of concrete is too thin, what is the preferred pour depth?

Be sure to tell your client that there are only two kinds of concrete: concrete that *has* cracked, and concrete that is *going* to crack. All you can do is try to make the cracks happen in the "right" places.

https://www.chaneyenterprises.com/Resources/Contractors/Concrete-Briefs/Concrete-Joints

hot_rod

DesignerDiana said:

We haven't built the home yet so any weight can be accounted for when we order floor trusses and steel basement beams. If 1 1/2" thick of concrete is too thin, what is the preferred pour depth?

You have it exactly right, gyp is a nice a self leveling product that gives you fire and soundproofing, but needs a finish floor over.

Maxxon Gyp-Crete High Performance is a 3- 4000 psi product that is used over steel corrugated decking instead of concrete. You can put a finished floor directly on it.
Standard 2000 psi gyp doesn't dry all that hard and you cannot tile directly over it. Floating wood or carpet typically.

I think Gyp Crete tried a 6000 psi product years ago that was intended to be a finished surface, but I don't see it offered any more.

With a thin concrete, 1-1/2" pour you need to use a 3/8" aggregate, so you get 1-1/2 the aggregate diameter over the tube. Over the tube that is the thinnest part of the pour and where it tend to "road map" crack.
3/8" radiant tube buys you a bit more coverage also.

If you do a thin concrete pour use poly fiber and 3 times the standard blend, 3-4 pounds per yard of concrete. The finish will look like it has dog hair all over it, but it does help limit the cracks traveling all across a pour.
If you want it to be a finished surface it needs to be power troweled as the friction melts off the poly fibers, and you can get a glass finish.

There are other additives to "soup up" the mix. Plasticizers make concrete it flow better, more like Gyp, and water reducing additives. The more water you add the weaker the mix, so using additives is a better way to get the mud to flow.
Air entrainment is another admix that creates micro bubbles that make the mix lighter and less prone to cracking. And it floats and trowels like it has ball bearings in the mix
Shrinkage reducing admixtures also.

If it is a hot sunny, windy day, retarder admixes can help get a good pour and finish.

Find a concrete plant that knows how to blend for radiant thin pours.

Zman

You can do a nice polished concrete floor with radiant. As Hot Rod points out, it is all in the details. I have done them with 2" concrete over 1/2" tubing. Be sure the structural engineer is aware of this upfront, hire the best concrete company you can find, and make sure whoever is specifying the mix has experience with this type of system. Small aggregate, high strength, and fiber reinforced.