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Electric radiant heat, overlay/topping and thermal break.

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GoZags

Hello,

Very informative forum. Been going over several posts related to my particular situation. This post is similar:

http://www.decorativeconcrete.com/content/radiant-heat-and-overlay

My particular situation is a basement in a 1930 home in climate zone 5 (dryer, eastern wa state). The walls are instulated and I'll be finishing the drywall this spring. It's not a large space (900 sq ft or so total). There is a finished laundry space and bathroom as well as utility area that I am not too concerned about (the finished floor, anyway).

I have a family/hangout area (L shape, 19'x12' extending to 20' wide) a small hallway and a bedroom (12'x13'). The entire floor (throughout basement) is concrete. In my opinion, it's pretty good considering the age. No buckling/lifting, etc. Some hairline cracks and pitting, but nothing major. By my estimations it's about 3-4" thick in most places. Certainly no insulation underneath given the age.

I did some tests and taped down plastic in a couple places to see about moisture build up and I didn't see anything (I did this over a period of time, through a couple seasons). Overall, the basment seems dry. It's not a damp, humid place (above average, anyway) in summer.

This winter I got one of those aimable temp gauges (laser pointer, works on walls, floors, your child's forehead). When it was 20f outside, the floor was 60f at the surface (avg reading). I have duct work in the basement but I keep the dampers off minus the laundry space, so to me, the floor temp wasn't actually that terrible.

That said, I am thinking that I would like to embed electric radiant heating mats/cables in at least the family area. Headroom is a concern, so every 1/8th inch counts.

I am fairly certain I could do this with ceramic tiles, but I would prefer the look and durability of concrete. I had a couple of concerns though:

The floor is slanted. Having it perfectly, horizontally level doesn't matter to us. Is there a topping that can be applied that can be hand troweled to a smooth finish? A non SLC product?

Everything I have read on plumber, tile setter and 'green' building sites said you have to have some sort of thermal break between the existing unisulated concrete floor, the heating wire and the top surface (tile, concrete overlay, etc).

I am pretty confident about the tile build-up using http://www.cerazorb.com/ as an anti-fracture/thermal break but, as I wrote above, I would rather have a concrete finish. Is there any product that can act as a thermal break and be topped by an overlay? Is that even possible?

Generally, the heating element in the floor would be a comfort/auxliary thing and not THE source of heat. I have forced air ducts and returns for that. But warm toes in a basement would be a nice thing!

Any suggestions as to a thermal break, or if for casual use could I get away with not having a thermal break and go with some sort of concrete topping?

 

Thanks

Dr J's picture
Dr J
Thermal break

I have put down the electric heating mats several times, using a topping material as the final finish. The product I installed did not require a thermal break and i don't understand why one would be needed. The heating cables came on a mat, which may have acted as such, I am not sure. The mat was held down by a few spots of topping material , let dry and then install topping as per normal.

Dr J's picture
Dr J
Thermal break

I have put down the electric heating mats several times, using a topping material as the final finish. The product I installed did not require a thermal break and i don't understand why one would be needed. The heating cables came on a mat, which may have acted as such, I am not sure. The mat was held down by a few spots of topping material , let dry and then install topping as per normal.

GoZags
Break

Thanks Dj.

From what I read and understood, the heating cables will be fighting the colder concrete below. Therefore not as efficient. A thermal break of any kind would be better than nothing.
Cerazorb is a synthetic cork, water resistant and is meant as a anti fracture and thermal break for tile - but I wasn't sure If an overlay of concrete would work over it or not. Or if anyone had any other suggestions.

I have seen some mats that are more mat and less mesh, that may offer some functionality. Would the concrete overlay need to envelope the mat/cables? Or if the surface area of the mat (maybe 50% of the total concrete area) is smaller, could the overlay cover the mat then bind with the surrounding concrete? (Picture a throw rug in the middle of a room).

Dr J's picture
Dr J
heat

Hello: Try going to www.ouellet.com and check them out. This is the brand I used. Campatible with Canadian and US codes. They have all the application uses and spec the thermal breaks if needed. Neat system, Simple to follow instructions and it works nicely. Installed toppings over them and acid stained. No problems.

GoZags
Suggestion from Watts

From what I have discovered after doing some poking around is that Watts makes a lot of the electric heating elements, even if they are sold under different names. This post here suggests that you do some sort of membrane or underlayment to increase the effeciency.

http://wattsradiant.proboards.com/thread/52/over-existing-uninsulated-slab

In particular they mention:

Custom Building Products' EasyMat
Wedi building panels
WECork's WECU
Noble Company's NobleSeal TS

Would one of these work with a microtopping?

What might that build up be?

clean existing floor

hardner and/or penetrating sealer, an epoxy?

thermal break mat

radiant mat or cables

top coat of concrete?

Thanks

Dr J's picture
Dr J
The brand I used suggested

The brand I used suggested cleaning the concrete surface and then sealing the floor. A W/B acrylic sealer would accomplish this. Glue down your mats and the encapsulate the cables with your topping material. Pretty simple.

GoZags
J, I'll do the prepping, as

J,

I'll do the prepping, as much as I can - but there are a couple outfits locally that I will investigate having do the final application of the topping material. 

Are there certain brands for some of these products that you might recommend?

 

thanks much

Dr J's picture
Dr J
What brands are available

What brands are available locally? I would try to find Mapie's ultra top...because they seem to be in a lot of locations. Use a high quality polymer topping mix.

Lindy A.'s picture
Lindy A.
As always Darryl (Dr J) you

As always Darryl (Dr J) you are a valued/experienced informational resource for all our our DCF members to tap into ... a Dr of Creteology, Sealologist, along with a true Concrete Surgeon. Really appreciate your high level of dedication as to assisting others.  In reference to heated floors (be they within the slab/internal hydro heated water piping; or ,the electric heat/connecting mat or wire/cable types that are placed on the top of existing substrate then encapsulated with polymer modified cementitous material/wear surface ), we don't have much of a call for them in Central Texas as you and those that reside in cold northern States & Canada do. 

GoZags
Thank you all.

Appreciate the assistance and knowledge sharing.