I have an old house with an uninsulated slab on ground floor.  I have a 10 foot stud, so I can afford to build up the floor a bit.  Is there a DIY-friendly technique to install hydronic radiant-floor heating in this situation?  I have looked at the alternatives of radiant ceiling and wall panels and there are significant difficulties with these, in my situation, so it might be better to go with the more efficient floor alternative if possible.

I'd like to go for a quick responding system rather than having a high -storage floor.  We have a mild climate and wouldn't be heating full-time.

Peter

I am noodling around with a product right now that would be ideal for that. It is called Bekotec from Schluter, the same folks who gave us Ditra tile underlayment. It's a 2' X 4' high density EPS foam sheet studded with "knobs" for an overall thickness of 1-3/8". The knobs facilitate looping of hydronic tubing. Then, you use a dry mortar pack to fill it and build up a minimum of 5/16" above the top of the foam knobs. After that, it looks like a cement mortar floor. You can install tile on top of that. Total height for the Bekotec and mortar screed is 1-11/16". Add another 3/4" for tile and you lose 2-1/2" to finish floor. The R-value for the panel by itself is R2.6, but you can simply lay additional EPS below it to any thickness if you want to increase the insulation.

It is very DIY. Cost is about $1.50/sf for the panels.

The dry pack mortar is just a mixture of Portland Cement and mason's sand. You can mix it in tubs on the floor until it is like damp sand. That gets shoveled and packed on the Bekotec, encasing the tubing and leveled with a straight screed.

I think I will use it to repair a living unit I have that was built on an uninsulated slab. The floor is so cold it is painful to walk on even when the unit is heated. I do have the height inside, but I think I will limit the amount of insulation I put directly under the Bekotec and put the majority of it around the edge of the slab instead. The small amount of insulation in the Bekotec will just serve to decouple the radiant floor from the existing slab.

for concrete overlayments we use/sell a similar product called Crete-Heat if you are overpouring. comes in 1", 2", and 3" thicknesses for the foam component. I recommend at least 1.5" of 'crete over that.

If you're looking for a dry system then you need a layer of insulation and sleepers, and then you can affix either an underlayment and your radiant assembly on top of that, or in some cases you can do a radiant assembly right to the sleepers.

Sounds like you have head room=options
I would suggest one of these choices:
A) 2 inch rigid Dow board type foam, staple pipe to foam or tie to wire mat then 3 inch over pour with cement.Now ready for tile, acid wash, floating wood floor, carpet
B) 2 inch rigid Dow board type foam, 4x8 3/4 plywood treated, RHT Floor panel system perpendicular to plywood ( This will tie the 2 together), Now ready for floating floor or nail down wood plank, Tile will require addition on wonder board or tile slip, carpet will require Masonite top.
Both systems will be similar in cost, The floor panel can move slower (many small bites to the system) 1 man show.
Dan

Thank you ICFHybrid, NRT,Rob and Dan for your helpful replies. I'm in NZ, so the brand names you mention will not be available but I can look them up and try to find generic equivalents.

With the thin cementitious systems, you presumably need to spread the heat flow with plates? You cannot use aluminium in contact with highly alkaline cementitious material like Portland Cement. I'm not too sure about copper either. What do you suggest?

Is it possible to stain and polish dry-pack, rather than tile?

Do you reinforce the concrete/dry-pack? Even if reinforced, it's a rather large room, so is likely to need shrinkage control joints, more of them for the very thin systems. What details are used for that? It's going to be a master bedroom, so I would like it to look good.

Lets leave the dry-pack out. It serves no useful purpose and can't be compared to cement or cementious material such as the original Gypcrete, which does not need aluminum plates.

The one thing to remember about any self leveling cement is that it is not structural so the substrate needs to be very solid. Gypsum cement is great but on any insulation, I prefer concrete, 3" min. Contact Terry at Enersol in Christchurch. He is the local king of heat pumps and floor heating.

Thanks for that Mike.

Hi Badger, in NZ dry-pack generally means zero-slump Portland cement mortar. English isn't just one language any more, if it ever was. Ever tried reading an English-language newspaper in India?

Peter

Thanks for that Mike.

Hi Badger, in NZ dry-pack generally means zero-slump Portland cement mortar. English isn't just one language any more, if it ever was. Ever tried reading an English-language newspaper in India?

Peter

Do you reinforce the concrete/dry-pack? Even if reinforced, it's a rather large room, so is likely to need shrinkage control joints

The Schluter product is a "modular screed system (which) allows the installation of continuous screed surfaces without any control joints or wire reinforcement". Schluter is from Germany, but sells world wide. Check out their website for a contact that can get you product in NZ.

Is it possible to stain and polish dry-pack, rather than tile?

No, the drypack mortar requires setting stone or tile over. Other compatible surfaces Schluter mentions are parquet, carpet or resilient flooring.

My drypack mortar consists of bags of "Sand Mix" obtained at the orange box store.  It is simply sand and Portland Cement in a 3:1 ratio.  I will add a bit of mason's sand to get to 5:1.  It takes the slightest amount of water imaginable and can be mixed on the floor in a shallow plastic tub with a hoe.  It looks like damp sand and sets hard.

The Bekotec product can also be used with a poured Portland Cement based screed. It can be poured up to an inch over the top of the knobs, but you'd have to call Schluter to see if they have recommendations for directly finishing that surface.

I like "dry pack". Thanks for the edification.