Tiling over screed/plywood floor with height differences.

Johnny · Jul 17, 2024

Hi guys.
Im a carpenter who has tiled a fair few floors over the years as i fit a lot of kitchens.
I have turned up today on a job and have been offered the floor tiling with ceramic tiles.
Its a big area (64sq/m) but a third of it is a new extension with a screeded floor. There is then a 12mm expansion gap before it hits a plywood floor on joists for the rest of the area.
To compound the problem even more the screed is 10 -12mm higher than the ply but only in some areas being level in others.
Can somebody who knows better than me advise on the best practise to overcome these issues and the best way forward.
The tiles are 600x300 and the floor has piped underfloor heating.
Its a situation i have not come across before.
All help is very appreciated so thanks ahead.

Tile Marble Granite · Jul 17, 2024

Johnny said:
Hi guys.
Im a carpenter who has tiled a fair few floors over the years as i fit a lot of kitchens.
I have turned up today on a job and have been offered the floor tiling with ceramic tiles.
Its a big area (64sq/m) but a third of it is a new extension with a screeded floor. There is then a 12mm expansion gap before it hits a plywood floor on joists for the rest of the area.
To compound the problem even more the screed is 10 -12mm higher than the ply but only in some areas being level in others.
Can somebody who knows better than me advise on the best practise to overcome these issues and the best way forward.
The tiles are 600x300 and the floor has piped underfloor heating.
Its a situation i have not come across before.
All help is very appreciated so thanks ahead.

send pictures

Johnny · Jul 18, 2024

Tile Marble Granite said:
send pictures

I will take some today and post later, thanks.

Johnny · Jul 18, 2024

Johnny said:
I will take some today and post later, thanks.

Hi, further investigation has revealed a chipboard floor with 6mm ply scewed on top

.

Tile Marble Granite · Jul 18, 2024

Johnny said:
View attachment 136366

Hi, further investigation has revealed a chipboard floor with 6mm ply scewed on top View attachment 136365 .

Anything level on that floor?

Kastar UK · Jul 18, 2024

Screw cement boards to the ply probably easiest fix to bring up levels ? Can get in 6 or 12mm

Johnny · Jul 18, 2024

Tile Marble Granite said:
Anything level on that floor?

The screed is level with the plywood in places and at its worst in the picture with the level ,must be 12mm difference.
I cant really pack the ply up because its only 6mm on top of chipboard.

Tile Marble Granite · Jul 18, 2024

Johnny said:
The screed is level with the plywood in places and at its worst in the picture with the level ,must be 12mm difference.
I cant really pack the ply up because its only 6mm on top of chipboard.

what about the screed, is it level along the timber floor?

Johnny · Jul 19, 2024

Tile Marble Granite said:
what about the screed, is it level along the timber floor?

Some places yes and some places its as much as 12mm higher than the wooden floor.
Am i right in thinking that even if i got the two floors level and then tiled over the two substrates the tiles will crack and that an expansion gap is necessary where the two floors meet.

Tile Marble Granite · Jul 19, 2024

Johnny said:
Some places yes and some places its as much as 12mm higher than the wooden floor.
Am i right in thinking that even if i got the two floors level and then tiled over the two substrates the tiles will crack and that an expansion gap is necessary where the two floors meet.

If the timber floor is level and the concrete is up and down, grind off the bumps. You can use a 7'' angle grinder with a diamond cup and a shroud to do so.

There will be a movement between the two floors. Out of the question.

Only the almighty knows if there will be cracks in that floor. Aren't you going to use an uncoupling membrane on top?

If the customer wants an expansion joint. Then do it and it is safer.
Most don't like the idea of having extra joints/trims on the floor.

Johnny · Jul 19, 2024

Tile Marble Granite said:
If the timber floor is level and the concrete is up and down, grind off the bumps. You can use a 7'' angle grinder with a diamond cup and a shroud to do so.

There will be a movement between the two floors. Out of the question.

Only the almighty knows if there will be cracks in that floor. Aren't you going to use an uncoupling membrane on top?

If the customer wants an expansion joint. Then do it and it is safer.
Most don't like the idea of having extra joints/trims on the floor.

Yes i would use an uncoupling membrane but i assume even this would not stop the tiles cracking.
Is an expansion gap the only option in this situation. She wanted the tiles brick style.

Tile Marble Granite · Jul 19, 2024

Johnny said:
Yes i would use an uncoupling membrane but i assume even this would not stop the tiles cracking.
Is an expansion gap the only option in this situation. She wanted the tiles brick style.

As far as I am concerned the tile shops sell uncoupling membrane as anti-crack. You can call the tile shops and ask

You can check out the US market, you might find different products: peel & stick, rubber membrane. All these products do the same as Dirta
The other option is the expansion joint

Johnny · Jul 20, 2024

On a side note is 6mm ply screwed to a chipboard floor acceptable practise for tiling onto ?

Tile Marble Granite · Jul 20, 2024

Johnny said:
On a side note is 6mm ply screwed to a chipboard floor acceptable practise for tiling onto ?

If it is solid then its ok, you will use uncoupling membrane on top.

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