The best primer and Adhesive for anhydrite screed

[J&K]

We have an Anhydrite screed floor laid last July and tiled in October. Screed depth 70-75mm. We tiled the floor before the UFH was commissioned, which reading this thread was our (expensive) mistake. The tiles have de-bonded from the floor and we have last weekend taken up 75sq m of 800x800mm porcelain tiles, salvaging about 50%. Inspecting the adhesive the primer is attached to it, so the primer has separated from the screed. We scraped the floor twice to remove the shiny top appearance, at 90 deg for each pass. This presumably was to remove the laitance? I assume there must have been trapped mositure that casued the de-bonding?
The average thickness of the adhesive is 20mm, and on one small area where we laid some levelling compound it has not de-bonded.
The UFH has been on during the winter for several days and for a week since removing the tiles. It must now be moisture free.
Having reordered replacement tiles, I would appreciate advice on what process to now follow in relaying the them.
I have read we should remove laitance which I assume is the top of the screed. How do we do this effectively?
Then should we use a Ditra type matting now that the floor is completely dry?
If no matting is recommended and we need 20mm of adhesive to bring the tile to the correct level height, should we use the Tile Master AnhyFix only, or can we use a rapid set flexible adhesive?
Appreciate any advice that can be given.

 

[newlineuk]

If you don't you ain't doing it right... :mad2:

Just checking.....

 

[Sean SML Tiling]

Did you do a moisture test before starting?

 

[Tile seller]

A standard anhydrite screed at 75mm would take 110 days to dry fully, (5 months), but depends on what was used.

Also, what primer did you use, did you dilute it and how many coats did you give it? Also what adhesive?

Did you follow the correct procedures for turning on the ufh?

Sorry for all the questions,just trying to see what went wrong so you don't get a repeat 🙂

 

[Sean SML Tiling]

I just finished a anhydrite floor and I got the customer to sign that the floor has been sanded then hovered then primed correctly to the manufacturer and gypsum adhesive was used. He also signed that 5 meter readings was done and that all 5 was below British standards 75% rh.

 

[Lee@emctiles]

[MENTION=45072]J&K[/MENTION] TileMaster also do a Anhydrite Leveller that may be an option for you to bring floor up to level?

http://www.tilemasteradhesives.co.uk/anhylevel

you might want to read relevant data sheets ect on Anhyfix as well http://www.tilemasteradhesives.co.uk/anhyfix

 

[Turkish tiler]

I think Kerakoll ....... Does best primer and adhesive for pump screed

 

[Unregistered]

No we did not.

 

[Unregistered]

We used Primer G product undiluted one coat and Mapei Proflexible adhesive.
We didn't commission the UFH before we tiled, which we now realise was incorrect.
thanks for your offer for advice.

 

[Stef]

J&K that is rather deep for putting addy on the floor to build it up, as Lee says I would use Anhylevel to bring that floor up to reduce the depth of the adhesive.

Unregistered, you must commission the ufh before you fix any tiles to the substrate & as Sean says you must do a moisture reading on these screeds to make sure the RH is 75% or below then it's good to go.