Substrates, porcelain,prep

[Versatile]

Just looked at a job where they are extending the kitchen to incorporate a garden room
Existing kitchen floor is concrete
New build to be anhydrite
What are the options for prep
I understand the prep for the new screed drying time ect
But would it be wise to de couple
Or could I just put a movement joint where they meet
Tiles are porcelain
Thanks

 

[Stef]

You must put an expansion join where the two meet.
On the gypsum side i wouldn't decouple with porcelain.

 

[J Sid]

no ufh?
treat each area as a separate floor with a movement joint between the two.

 

[Versatile]

Yea new screed had water ufh
I'm doing the kitchen first because of new kitchen being booked in
Then new when dried commissioned ect
Cheers

 

[Versatile]

That should have read will have ufh

 

[J Sid]

Ditra or similar on new screed once dry and ufh commissioned. Plus expansion / movement joint between the two

 

[AndY mac]

Hi steff. Why would you not decouple gypsum for porcelain. Had a job recently where the builders joined the floors but was not a straight join up down left to right. Decoupled then laid 600x600 porcelain. No other solution.

 

[Flintstone]

Why decouple with porcelain ?

 

[Stef]

Hi steff. Why would you not decouple gypsum for porcelain. Had a job recently where the builders joined the floors but was not a straight join up down left to right. Decoupled then laid 600x600 porcelain. No other solution.

You've not got the same shrinkage as you have with a cement screed, I would still break it across doors as these are natural areas where a screed will crack.
For belt & braces then you should use a decoupler but as porcelain tiles are quite robust I wouldn't use it.
You say the builder joined the floors, in that circumstance your trying to use a decoupler for what it isn't really designed for. It really should have an expansion between floors.

 

[AndY mac]

If I used a expansion it would have looked terrible. What else could I have done?

 

[Flintstone]

Not a lot by the sounds of it, I once had a floor with two substrates and a weird joint and I had to lay a decoupler over the joint between substrates. About 1m wide all way across.

 

[hmtiling]

A colour coded Silicon joint would do the trick with porcelain. Or Dural microjoint with stone which gives more protection to the edge

 

[AndY mac]

I don't no of any other product I could have used. The join was like a castle rampart.

 

[Stef]

If I used a expansion it would have looked terrible. What else could I have done?

There's nothing that could have been done tbh, you have done the right thing by trying to address the problem but a decoupler is no way supposed to be fitted instead of an expansion join.
I'm not wanting anyone reading this thinking that they can do away with an expansion join.
We as Tilers push the boundaries of our trade as we have a fair idea of what will work & what won't, it's down to years of experience but again not wanting someone to read this & think it's acceptable to not fit an expansion in tile face when there is one in the substrate.

 

[widler]

I don't no of any other product I could have used. The join was like a castle rampart.

Expansion joints look poo in domestic houses , like has been said, just use a coloured Silicon along the grout joint instead