Thickness of flexible tile adhesive for terracotta tiles on anhydrite screed

[piggy]

Hi - We are nearing the end of a self-build project and have hit yet another brick wall!
We have 100m2 of floor to tile with 25mm thick terracotta tiles over UFH. They are a bit uneven and the makers recommend bedding them on a 15-20mm mortar bed, our tiler wanted 25mm in order to do a good job so we left space for 25-30mm.
We have laid a gypsum screed over the UFH and the advice seems to be to use a flexible tile adhesive 10mm thick (after priming).
We have been supplied with Primer G an acrylic primer supplied by flo screed.
Please can anyone tell us what we can successfully use 25mm thick?
:mad2:.
Many thanks to one of your threads on preparing gypsum screeds for tiling it was more informative than a whole day spent elsewhere on the internet.
Piggy

 

[Gazzatile]

I have used Mapei P4 as thickbed adhesive but cannot remember what max dept is may be only 20mm Just looked on website is only 20mm

 

[diamondtiling]

25mm is on the excessive side for an adhesive bed, you could lift the surface with a flexible self leveller to leave you with 15-20 mm which is more than adequate.

 

[Perry]

who are the makers ?

 

[piggy]

Thanks for that- Mapei website wouldn't come up for us last night but found some stuff on the Bal site at about midnight - pourable thickbed up to 25mm. Main thing is to know that there's a solution out there to be found!
Is it ok to use a different make of primer to the adhesive - all the makers obviously recommend their own primer but we've already got primer G courtesy of Floscreed

 

[piggy]

That sounds like an interesting idea - have to chew it over.

Quite honestly would like to put down a plastic film and fill the void with mortar + additive and bed the tiles on that. That would decouple from anhydrate screed, waterproof and reduce costs - but i'm expecting at least 20 replies to that suggestion telling me i'm barmy.

Thanks for your reply

 

[piggy]

Do you mean the tiles? if so York Handmade - lovely tiles, don't want to wreck them!

 

[DHTiling]

How long has the screed been poured..? and is it a low laitence type..?

 

[piggy]

Hi Dave

The screed was poured about Nov 1st - We have just delayed tiling when we discovered that the screed needed to be .3-.5% moisture content - bogglingly small - but thank god for the internet!
We are now about to install gshp on a plinth in the utility to help achieve this before going any further as it seems that the best chance of a successful outcome will be achieved by heating the slab first.
Yes the screed is low laitance.
Thanks for your interest

 

[DHTiling]

You are right it does need commissioning first.. and the portable gshp will be great..

My concerns are using that depth of adhesive or modified mortar.. are the tiles that bad in calibration to require such a bed depth..?

 

[Ajax123]

That sounds like an interesting idea - have to chew it over.

Quite honestly would like to put down a plastic film and fill the void with mortar + additive and bed the tiles on that. That would decouple from anhydrate screed, waterproof and reduce costs - but i'm expecting at least 20 replies to that suggestion telling me i'm barmy.

Thanks for your reply

not sure why you can't do that. would not be plastc film as such but Ditra or Dural matting or the like.......

 

[Perry]

i would have thought morter bed was the worst thing you could have done with terracotta but i have only laid 2000 - 3000 mts in my 29 years of tiling looking at their specs i dont think they no a lot about fixing them imo or have i got it all wrong ?

 

[piggy]

You are right it does need commissioning first.. and the portable gshp will be great..

My concerns are using that depth of adhesive or modified mortar.. are the tiles that bad in calibration to require such a bed depth..?

Hi
Thanks for replying, Had intended to install gshp on floor once tiled but 'best laid plans'!

The tiles are not so badly calibrated in fact, but that is the gap that we have left to be filled to get the floor level to meet the threshold level to meet building regs.

What 's the problem in using a thick bed depth of adhesive or modified mortar apart from the cost of course?

 

[piggy]

Only problem with Ditra is that they don't recommend putting more than 10mm thickness of adhesive on top of it. Don't know if Dura and Genesis etc say the same but would expect that they do.

 

[piggy]

Hi
Thick bed mortar was what the tile makers recommended even on a heated mortar screed.

We have since laid anhydrite screed for what seemed like good reasons at the time thus increasing the gap and causing our current headache,

What do you use for terracotta?