mixed substrate

[groucho]

Hi all quoting for job in kitchen and customer wants UFH. its 30 sqm very odd shape going from kitchen to conservatory. so normal probs floor height issues. 6mm thermal boards down, UFH down, self level, tiles comes to about 23/24 mm. kitchen is floorboards conservatory is concrete so question is im concerned about how the 2 substrates react to UFH. Is thermal boards on there own ok? or do i need ditra on top as well to help with the movement? floorborads when UFH is on will do one thing concrete will be doing something else. Its alot more money and raises the floor level again if I have to put ditra down. im sure somebody has had this prob. cheers

[garythetiler]

i would use 2 ufh mats into 2 areas so it doesnt bridge the different substrates if you are putting thermal boards over the whole area again I would break these where the different substrates meet and put an expansion joint in, there is no need to use ditra as well as insulation boards in my opinion unless it is natural stone you are fitting then I probably would use it

[groucho]

so would you have to start with a full tile on the join where the two substrates meet? coz the whole set up would have to be off that line or just cut the tiles on the join and put an expansion joint in. yes going to have matts down one area is a lot colder than the other

[garythetiler]

I cant give any advice on the set out groucho as i would need to know what size tile you have and a diagram of the rooms but if you can set out a full tile from the ej and it works well then i would be inclined to do that rather than cut the tiles through it which type of tile are you fitting ?

[hillhead]

You cant really let expansion joints control your layout.you want decent cuts at kicker boards.doorways and skirtings etc.you need to lay it out well before starting.i tiled a hallway/kitchen/utility and toilet floor earlier in week and had to connect all.i had to pull 20mm off centre of hallway to make rest work for me.turned out well.good luck with your job.

[groucho]

customer hasnt chosen tile yet. but exp joint will look shxx if it goes through middle of tile. however if it has to go in then thats that and customer will have to realise its needed. thanks for the advice

[Rob Z]

Hi Groucho,

I agree with Gary and Joe....the expansion joint placement has to control the entire job, regardless of what the customer does or doesn't want to see. The floor and the tile are going to do what they are going to do, and that "break" is going to occur at the change of substrates.

It's frustrating having to argue with people over this, but you have to stick to your guns and tell them the way it has to be.