Slate Floor Electric Underfloor Heating

Lottie

Hi

Need a bit of advice on the compatability of the above.

We have 60x40 Natural slate tiles that will be laid over a screed.
The natural slate has some pretty big variations in the thickness so our tiler has said they would need to be laid with a 'dot and dab' approach and then a 'slurry' grout.

We have also purchased under floor heating of the cable (not the mat) variety.

We have been told that the underfloor heating will not work with these tiles. In fact we were told that no underfloor heating will work with these tiles and that you would only feel the heat around around the grout with a cold spot in the middle.
This is contrary to everything we've read so we're now confused.

The tiler said that if the underside of the slate was polished it would work but because of the natural surfaces on the tiles due to the splitting process it won't work.

We're really unsure if the tiler just doesn't like laying underfloor heating cable or if he's right!!

Any advice would be very greatly appreciated

Many thanks

Lottie
:confused:

jbfan

I can't answer the question you ask, but I can see that it might not work as well because of the differant thicknesses of the tile. This would seem to leave some gaps where the heat cable may not come into contact with the tiles.

__________________
Yes I am a Pirate, 200 years too late. "Jimmy Buffett"

Steven62

Well, late news, and good and bad...

Slate is one of the hardest stones to heat, but it's a two edges sword. It takes longer to heat up, but it holds the heat longer. With the variations in thickness, you may feel differing temps during the warmup phase, but once warmed the heat will naturally radiate to all parts of the stone.
If the wires are spaced properly, ( I dont know the specifics of the brand, but Suntouch Warmwire can be spaced at 2" intervals yielding 15 watts per sq. ft., about 51 BTU's/Hr)
Then it should heat O.K.
It should definitely take the chill off, if not provide some additional heat to the room, depending on stone thickness, and heat loss from that particular room.

High Ground

I have VERY uneven chunks of slate on my floors and would like to fit wet underfloor heating along with a heat pump.......... does anyone know if this would work? would I get enough heat through the lumps of slate, Im sure some are several inches thick !!

Steven62

So...Is this an existing stone floor? On slab? or Framed?

If it is done right, hydronic is capable of higher temps than electric systems and it is possible to heat several inches of stone and/or mortar, but I would need more specifics on the construction.

Do you have space for a boiler & panel? Do you have one existing?

Give us more to work with & Im sure we can make an informed statement!

Daniel Holzman

I assume from the post Bob that you sell underfloor heating. I don't sell the product, but I did install electric underfloor heating in my kitchen underneath stone flooring.

The thickness of the stone only affects the amount of time it takes to heat the stone, as has previously been noted. This is due to the thermal mass of the stone, obviously you have to heat the stone up before it starts radiating, and the thicker the stone, the more time that takes. However, there is no problem doing so, it simply takes longer to get warm, and of course longer to cool down.

There is no problem about the wires not touching the stone, the wires never should touch the stone, as they are supposed to be bedded in mortar. You can go to the Suntouch site for explicit directions on installation technique, most of the products use a similar approach, i.e. bed the wire or mesh in thinset, then install the stone tile over the thinset. I used Ditra on my floor, so the Ditra went over the thinset that encapsulated the wire.

In order to direct the majority of the heat into the room, it is generally recommended that you insulate the underside of the floor. I used foil wrapped bubble insulation on the ceiling of the basement under the kitchen, which reflects infrared heat upward, as well as providing some insulation. You can get the foil wrap at any big box store.

You can go to the Schluter website for a thorough discussion about installation of electric heat under a tile surface. Good diagrams, easy to follow instructions. If your tile installer is not familiar with installation of wire heat, you should probably get someone else to put the wires in, it isn't really difficult, but you have to check the resistance constantly to make sure you don't damage the wire during install, and the electric hookup for the thermostat is probably beyond his skill set if he has not done it before.

IceT

don't go for slate .. it isn't a good floor with the infloor heat.. or so i have heard.