Installing Underfloor Heating

[MartinH]

First time job for me....bit apprehensive tbh, as to date have only done standard wall and floor tiling, but you have to takes these jobs on, as they are becoming more the norm ......

I have been to see the bathroom, and from what I can see, its a pretty sturdy wooden floorboard set-up - I explained that there would be a floor height build-up, and they wanted to try and keep that as minimal a possible ......

Could someone please give me a topline as to the construction makeup ...im thinking, but you are more the experts

1. Thin plywood cover screwed to floorboards (6mm?) or do i need this at all
2. Backerboard over top screwed down (does this need to be a certain type as its going to have underfloor heating mesh on top?)
3. UFH mesh
4. SLC over top (again any specific one needed?)
5. Flexi Adhesive (powder based)
6. Tiles on top
7. the local vicar to come and bless it before anyone walks on it

...any advice greatly appreciated.....before I put my head into the lions mouth!!

whilst on here and off topic, does anyone know where I can find the chart that shows weight loads for stud walls - I am trying to convince this customer that tiling overtile is not a good idea following previous advice on here, explained that there was a weight load consideration and he has asked if I have the info to hand...which I didnt at time...im sure he will take heed if I can show him the "dangers" of this approach

[Dan]

I'd replace the floorboards with 1§8mm ply, then use a backerboard, then heating mat, then a flexible SLC (any good make), flexible adhesive (fast setting or slow, depending on your speed), then tile, then grout.

[jwatson]

1. Substrate weight ratings

A common question, how much weight can my wall support, here are the recommended max weight ratings in KG / m2

Plaster Skim on Plaster Board........20KG
Skim and Set Plaster...................28KG
Plaster Board.............................32KG
Sand and Cement.......................40KG
Cement Backer Board..................55KG
Hardibacker Board.......................45KG
Lightweight Tile Backer Board........40KG
Glass Reinforced Cement Sheet.....50KG
Gypsum Fibre Board.....................40KG

Remember to factor in the weight of the tile / m2 AND adhesive and grout
2. (Some adhesives are manufactured as lighter products).
3. grout weight will also depend on how large the tiles are that you are using and the thickness eg a tiled area that uses 300mm tiles will have more grout than an area with 600mm.

Grout.........2KG / m2
Adhesive....4KG / m2

[MartinH]

1. Substrate weight ratings

A common question, how much weight can my wall support, here are the recommended max weight ratings in KG / m2

Plaster Skim on Plaster Board........20KG
Skim and Set Plaster...................28KG
Plaster Board.............................32KG
Sand and Cement.......................40KG
Cement Backer Board..................55KG
Hardibacker Board.......................45KG
Lightweight Tile Backer Board........40KG
Glass Reinforced Cement Sheet.....50KG
Gypsum Fibre Board.....................40KG

Remember to factor in the weight of the tile / m2 AND adhesive and grout
2. (Some adhesives are manufactured as lighter products).
3. grout weight will also depend on how large the tiles are that you are using and the thickness eg a tiled area that uses 300mm tiles will have more grout than an area with 600mm.

Grout.........2KG / m2
Adhesive....4KG / m2

Fantastic - thanks very much for this info

[GirlRacerRed]

to convince your customer about weight issues, have a look at the links below:

weight limits when tiling a wall...

and

Planning & Preparation
look for the section down the page marked Wall Tiling Preparation

[jwatson]

if customer is wants the job doing properly. tiles on wall need to come off realy, you cannot see/know what the original substrate condition was in before it was tiled just advise how many boxes of tiles are needed to complete your m2 and then multiply by 2 hopefully they will see that the weight is a real issue.
ultimatly you will get a better finish, and you as a professional will be happy with the finish which inturn they will be. good luck.
will post some info on ufh.

[jwatson]

Tiling over screeded floors with UFH
Allow cement screeds to dry out for three weeks, unlessquick setting cement used. Once dried out fully, turn on the UHF an allow it to heat 5 d/c per date, until a temp of 25 d/c is reached, leave the UHF on at 25 d/c for three days then allow it to cool to normal room temp. Once tiled leave the UHF off for two weeks, then raise the UHF to desired temp at no more than 5 d/c per day.