Tiling over mixed subfloors - experienced opinions needed

[Joh]

Hi .. I'm a new member and a DIYer .. I've a job to do on my own house which is too big for me and it's complex .. I have asked 4 tilers (all seem pretty clued up and a couple are "recommended") for advice and prices. However there are differences in opinion about how to deal with the UGH, the wooden floor and the junctions between the different subfloors. I would like to get some more experienced views to help me come off the fence!

The job is a large open-plan area including an extension/garden room (32m2) with a wide walkway (5m2) leading to a kitchen (16m2). All three sections have different sub-floors.
The extension (in progress) is due to have a solid floor, with wet system UFH and sand/cement screed over.
The hallway joining the extension to the kitchen has a solid concrete floor partly covered with terrazzo tiles - no UFH here.
The kitchen has a very stable suspended floor (includes sleeper wall) - timber joists with T/G floorboards, covered with 6mm ply (stapled at about 200mm centres) covered in Karndean tiles. (Did the jump-up-and-down next to a glass of water test on the floor - the water hardly rippled.)

Although the Karndean is good, it would look briliant to have the same floor running throughout so the idea is to cover the area with either porcelain or tough ceramic tiles.

Please - how should I proceed to ensure the tiles don't shift?
NB I'd like to have as little change in the height of the kitchen floor as poss given that it is already a little higher than the main hallway of the house. At the same time, I don't want to risk the quality of the tile job .. aagghhh!

[Dave]

Hi Joh...

Firstly regarding the 3 different sub-floors...

You will need a movement joint between each change in substrate...this joint needs to be exactly over the break in the substrates

So that's a joint between the garden room and kitchen and hallway....

The kitchen floor needs that ply replacing with a 6mm hardi cement board , this will keep the height down between the garden room and hallway....and make up any differnce either with SLC or continue through with the hardi but don't forget to leave a joint over the substrate break for expansion / movement...

The movement joints can either be preformed joints or you can use a cold joint( silicone) matching colour to grout...

The cold joint is less noticable and looks better in a domestic situation..

You can tile over the terrazzo tiles if they are solid and cleaned first...

Use flexible adhesives and grouts as well...

[Joh]

Cheers, Dave .. that's more or less in line with what one of the tilers I've spoken to said .. the only difference being he also recommended using an uncoupling membrane over the extension because of the UFH.
What is the function of the Hardi backer?

[Dave]

The function is it ti give a better base to tile to than the floorboards and is more moisture stable than ply...

If you were putting stone down then i too would have recommended an isolation membrane..but not really need with a vitrified tile like porcelain...as long as perimeter joints are left and the cold joints between substrates then no probs..

[Joh]

I see ... so, could we use detri mat instead of the backer in the kitchen? It's supposed to be water proof (which might be advantageous in kitchen setting?) and gives a reasonable surface to tile on I think? It's a bit thinner, too, and this would ease things a bit regarding levels.

[Dave]

You could Joh , If the floor is 100% deflection free......The Hardi board will give strength as well as moisture control....the Ditra is only for lateral expansion and water proofing..

Don't get me wrong the Ditra will give a excellent base but it needs to be solid..

[Joh]

By gum you're quick replying! .. thanks for the help - it's very much appreciated .

Oh .. and is it possible to shift my post into the main forum?

[Dave]

Oh .. and is it possible to shift my post into the main forum?

Certainly..

[Joh]

I've just got a good price from a chap who has a very good reputation locally .. old school, done loads of work in the area (shop floors, big houses and the like) .. I'd appreciate some thoughts on what he advises cos it's a bit different ..

one expansion joint where the UFheated floor meets the concrete (not heated).. he doesn't think there needs to be another one between the concrete (not heated) and the kitchen (wooden suspended) as the concrete area isn't very big .. he thinks the karndean and ply needs to come up, the T/G needs to be screwed down then tiles fixed on top using thick bed flexible adhesive .. it would need to be thick to compensate for the 3mm difference between the height of the T/G and the concrete .. he reckons the adhesive will cope with any movement .. he doesn't comb off the adhesive, by the way .. he butters the floor and tiles, then levels using pressure and spirit level .. his jobs look very good from what I've seen
Your thoughts?

[Dave]

So he wants to tile direrctly onto the floor boards with a pourable thick bed adhesive......It needs to be an S2 quality adhesive and noggins inserted every 300 mm between the joists for extra support for the floor boards..That's why over boarding is recommended..

The timber expands at a different rate to the concrete , so how will he over come this by tiling over the break in floors.?..what if a small amount of deflection is present...how can the tile cope with that between the timber and concrete..?


Just coz his jobs LOOK good dosen't mean they are done correctly...


If you are looking for a tiler...why not let us get one for you..?

[mozzy]

The timber expands at a different rate to the concrete , so how will he over come this by tiling over the break in floors.?..what if a small amount of deflection is present...how can the tile cope with that between the timber and concrete..?




he would have to use schluter ditra as its an uncoupling membrane and will absorb the movement of the timber and concrete which will prevent cracks occuring in the tiles.

[smurf21]

joh take my advice and listen to Dave he's spot on, your floor is going to cost get it right first time.

[Dave]

The timber expands at a different rate to the concrete , so how will he over come this by tiling over the break in floors.?..what if a small amount of deflection is present...how can the tile cope with that between the timber and concrete..?




he would have to use schluter ditra as its an uncoupling membrane and will absorb the movement of the timber and concrete which will prevent cracks occuring in the tiles.

Schuters Ditra is only designed to cope with lateral expansion and not deflection....

[Joh]

Been away for a few days r and r .. thanks for all the help with the sub-floor question .. what I propose doing is:-
- pulling up the karndean and ply in the kitchen
- securing the T/G with screws (joists seem sound - if not fix these too)
- using a layer of backer board over the T/G
- slc over the terrazzo if needed to ensure smooth transit from the backer board (kitchen) to the new screed (extension)
- then ... tile away (with expansion joints at perimeters and where there are changes of sub-floor)

Hopefully a sound job ...

Thanks again!!