the correct adhesive method over under-floor-heating - TilersForums.co.uk | Tile Forums

30-03-2008

Hi all, i am just about to spend a lot of my hard earned on having underfloor heating and tiled floor in my kitchen-diner. I always leave these jobs to the professionals but like to educate myself a little to avoid being taken for a mug. Once the underfloor heating is laid in a self leveling latex type stuff what method would you use with the tile adhesive? should i expect complete coverage under the tile or can you use a lump in each corner and one in the middle? sorry for the layman description but all help would be most welcome. Many Thanks, Steve.

**grumpygrouter** · 30-03-2008

Hi Steve, if you registered with the forums, we would be better able to keep track of your query regarding further questions and answers.

I assume you are talking electric UFH here? It is normal to lay the heating mats on insulating backerboards first of all. Then, I always lay self smoothing compound on the top to protect the cables and give a better surface for tiling on to. Adhesive should be laid to provide a solid bed underneath the tiles. Dabs in the corners and centre of the tiles ARE NOT acceptable!

Grumpy

30-03-2008

Cheers Grumpy. is it acceptable to have any voids under the tiles? the truth is they started laying the floor the other day and my wife said she saw him laying with a dot and dab method. the floor is nearly finished, so am i to assume that the electric underfloor heating wont penetrate the tiles because of this? i dont think i'm going to like your reply......gutted.

30-03-2008

Cheers Grumpy, just registered. To be honest they started tiling last week and my wife said she saw them using the dot and dab method. Can i assume that if there are voids under the tiles that the electric underfloor heating wont work properly? cheers.

**Sir Ramic** · 30-03-2008

Dont use dot and dab. If you do the tiles will sound hollow, they will be prone to breakages and infestation of insects etc.
Lay the UFH and either as Grumpy states SLC over the top and tile at a later stage. Or you could tile straight over the UFH but this can be tricky as you may damage the UFH elements. Using a plastic notched trowel will help if you choose the later method.
I would go with Grumpy and Lay UFH and then SLC. Better job in my opinion. You only need to cover the UFH with SLC as the more SLC the harder teh UFH has to work to get heat up to the tiles.
When laying i would spread the floor with a notched trowel and depending on the tile chosen you may find buttering the back of the tile will be needed too.

**grumpygrouter** · 30-03-2008

Quote:

Originally Posted by steve3

Cheers Grumpy, just registered. To be honest they started tiling last week and my wife said she saw them using the dot and dab method. Can i assume that if there are voids under the tiles that the electric underfloor heating wont work properly? cheers.

You quite catagorically DO NOT want voids under the tiles. Not only does this reduce the efficiency of the UFH but the tiles will be much more prone to breakages - stiletto heels will penetrate them - Also I do believe that is contravenes British Standards but don't quote me on that one.

If they have Dot n Dabbed then I would be inclined to ask them to start again!

Grumpy.

**Sir Ramic** · 30-03-2008

You should be able to tell if they have " dot and dabbed" by gently tapping the tiles with something like the end of a broom. If they have dabbed then you will get different sounds from the tile. A coin etc can be used too just be gentle, you dont have to tap too hard.

**enduro** · 30-03-2008

I bet you wish you hadnt asked now Steve...

30-03-2008

Quote:

Originally Posted by enduro

I bet you wish you hadnt asked now Steve...

well i would rather know and i thank you all for the advice. The only saving grace is that i havent paid yet (apart from the tiles which i sourced, which are 600x600 porcelain) and i wont hand over any money until i have fully tested the underfloor heating, which by all accounts takes a while as you have to up the temp over many days by 1 degree a day? and if i'm not completely satisfied by then i dont know where i stand in making them do it all over again.....i dont think i could take all the upheaval.

30-03-2008

we had some under foor heating installed and the guys tiled straight over the matting, no self level compound at all.

i watched them because i was worried about the cables being cut but, they spread the adhesive flat with the flat side of their trowels so the adhesive covered the wires and then they used the serated adge to plough their lines. is this correct or wrong, id like know for future ref

thanx

**Sir Ramic** · 30-03-2008

There is nothing wrong there Lady tiler. Its just that some prefer to use SLC before and tile at a later stage.

**Holohana** · 30-03-2008

hi Steve3. If you do ask them to rip up and start again because they have dot & dabbed then this will almost definately damage you ufh cable unless they are very carefull.