Anhydrite Screed Question - TilersForums.com

[Element]

I have a problem developing with tiles laid over water UFH in anhydrite screed. A few tiles are sounding hollow and are slowly becoming loose. The floor was 'scarified' using an orbital floor machine with a rotating disc with points underneath. The floor was then treated with a primer apparently suitable for anhydrite screeds ( Prime Plus | Flexible Primer & Bonding Agent | Tilemaster Adhesives ) following its precise instructions. The tiles were then laid using a 10mm bed of standard Tilemaster Setaflex.
I have been told that anhydrite screeds should actually be sanded and then primed and I'm now wondering whether the scarfyer process wasn't adequate for the primer to give sufficient bond strength for the adhesive? It was the first and only occasion I have laid tiles over water UFH. I am returning to the client tomorrow to offer to lift a tile to look at what has happened beneath...

Your opinions would be appreciated!

 

[hmtiling]

Any reason you didn't use Anhyfix?

 

[hmtiling]

What are the tiles?

 

[White Room]

Setaflex bothers me....

 

[One Day]

Setaflex bothers me....

cement onto gypsum bothers me! what was the moisture content, how deep the screed, how long down.... So many checks needed before fixing to anhydrite. And extra checks needed if going cement without an uncoupler.

 

[Chalker]

As above. Firstly was the screed commisioned and dry before tiling?

 

[Lee@emctiles]

i dont have an issue with the use of the setaflex, as this WAS the way alot did it before TM came out with Anyfix.

FYI here is the technical data sheet for Anyfix

 

[Element]

I had never heard of Anyfix until today.

However the update is the screed was 50mm deep, left to dry six weeks before the screed company scarified the surface (IMO, they did a pretty poor job too) I then applied the primer and tiled on top. No moisture reading was done; I didn't know (then) a reading was necessary, and have never used a moisture meter & nobody mentioned it at the time despite my asking as much info as I could locally with suppliers & builders.

I spoke with TM today and they said that an anhydrite screed should dry for 7-10 days and then be sanded to allow the moisture to escape. The screed company didn’t do this. Then in an ideal world the UFH should be commissioned incrementally to further aid the screed to dry and only when the floor is dry should the priming & tiling be done. The plumbers didn’t commission the UFH until 3 weeks after the tiling was completed.

Today I lifted one tile and found the adhesive fully bonded to the tile and the primer; the tile pieces came up with the adhesive & primer intact as one leaving the anhydrite floor clean beneath. The primer under the tile was damp to the touch. Now I know why; the floor was not adequately dry when the primer went down and further sealed the moisture in. With the UFH on now, the moisture is causing the bond of the primer to the screed to fail and the tiles are loosening up. I suspect the whole lot will need to be removed and the floor fully dried out before another covering goes back down.

It’s been a bad day.

 

[J Sid]

Thanks for the truthful update.

 

[Chalker]

Feel for you!

As more liqud screed us used, your problem is becoming more frequent.
Maybe all tradesmen should reaserch before fitting to any surface and be sure they are using the correct methods.
But as usual.it's normally a case of, until it happens to you.

I think the onus should be down to the screed companies. They should supply a simple data sheet with every pour, to say drying times and ufh comisioning . Then info on processes before and during laying flooring.