Tile on anhydrite

[kiero]

Hi all, I'm new to this so please bear with me.
I have a problem with my floor tiles that had been laid on to an anhydrite screed. Floor was apparently prepared as per instructions but a few months ago I noticed white powdery substance coming up through grout.
I will try and attach 2 photos (back of tile and screed surface after tile removed, not cleaned in any way) i would appreciate some opinions from professionals who might have seen similar before.
After lifting further tiles cracks were uncovered in the screed in one room but not any other. Also, tiles to other areas have remained intact and are at present sound.

Again i would greatly appreciate any comments.

Many thanks,
Kiero.

 

[Ajax123]

Sounds like efflorescence which would suggest the screed was either wet (very wet) or the adhesive overwatered.

More detail will be needed o diagnose

What adhesive
what primer
how long was the screed down
what prep
is there ufh and was I comissioned and up to what temperatures

 

[kiero]

Hi Ajax,
Screed was down 60 days (approx) before tiling, adhesive was Larsen professional fast set, primer was Larsens (pink colour) and underfloor had been on whilst screed dried and flow temp of approx 35-40 degrees. Tiler maintains that moisture had been checked and was ok to proceed.
I can't understand how other rooms are sound and these 2 are failing (all tiled in succession).
I cannot get photos to attach but I have seen similar posted before on this forum -White substance on rear of tile and no adhesive has remained on the screed at all.
With regard to cracking, if adhesive was properly applied and cracking of screed occurred would the tiles not also crack?

 

[Divad]

Sounds to me like tiler error. I bet he didn't sand the screed before priming. Cowboys.

 

[kiero]

Cheers Divad, the guy who laid the screed was responsible for sanding and hoovering dust etc.

 

[Ajax123]

Does the white substance look like dust or is it chrystalline and very white.......if the latter it will be ettringite. Where in the country are you??

 

[The D]

Sounds to me like tiler error. I bet he didn't sand the screed before priming. Cowboys.

Whatever !!!!

 

[kiero]

It seems to be like the latter, I had been told that this may be the substance. Would this cause tiles to 'debond'?

 

[Ajax123]

It seems to be like the latter, I had been told that this may be the substance. Would this cause tiles to 'debond'?

Ettringite will destroy the bond between the tile adhesive and whatever it is stuck to. It is a chemical reaction between the sulphates in the moisture in the screed which come towards the surface on drying and the calcium alluminates in the cement. If there is no moisture present then the action does not happen. The idea of the primer is to prevent the reaction by divorcing the two materials but sadly I see a lot of failures of this nature where the primer has been used poorly or the screed has been excessively wet. The 60days may not have been long enough depending on the depth. Also you need to make sure the heating is comissioned and run as this will cause a burst of moisture (allbeit only a very small amount) to rise to the sirface which could over load the primer. Sometimes itis simply a case that the primer does not work.....?

Some of you will realise I am a it advocate of gypsum based adhesives. Some feel that these are still being tested but realistically they. Have been around for years in Europe and are well and truly tested. The other type is kerakoll h40 ideal or benfer gys from benfer. Many of these can be used without the need for primers so that has a major risk management advantage as well.


There will ALWAYS be some ettringite within the cement as there is gypsum in the cement but the level is theimportant but.

 

[kiero]

Thanks for that Ajax, i am starting to think this is the problem with my floors. A final query for you all, tiler reckons that laitance was not removed correctly. If this was the case would the tiles in other rooms not react the same? and should he not have noticed this at the start prior to 'priming'?

 

[Ajax123]

Thanks for that Ajax, i am starting to think this is the problem with my floors. A final query for you all, tiler reckons that laitance was not removed correctly. If this was the case would the tiles in other rooms not react the same? and should he not have noticed this at the start prior to 'priming'?

Yes and yes.