Anhydrite laitence removal - Tile Advice

[Dannym80]

Yes it's that damned gypsum screed!
The builder assured me it's been sanded & laitence removed all bar one room. I'm on site today and they've got a guy using an electric hand sander with 80 grit paper. I don't think that's manly enough, how can I tell if the laitence has been taken down sufficiently?

Thanks in advance

 

[Qwerty]

You should be able to see and feel it is different in texture & colour. How long has it been down? Has UFH (if fitted) been correctly commissioned?
I had to try and remove laitance from a screed which had been down and commissioned for some 8 months. Was a nightmare I tell you!

 

[Dannym80]

It does have wet UFH and has been commissioned correctly, the floor has been down for around 16 -17 weeks. Ive had a little scratch at it & i have to admit I can't really tell!

 

[Qwerty]

You will struggle to get the laitance off with a hand sander after this amount of time. Laitance should really be removed much sooner...... around a week or so after pouring depending in drying conditions, thickness etc. Any pics?

 

[Dannym80]

In the shadowed one is how the majority ofnthe floor looks, in the other you can see a small lighter patch where i had scratch at it with a key.
Hope this is helpful

 

[Dave Mitchell]

In the shadowed one is how the majority ofnthe floor looks, in the other you can see a small lighter patch where i had scratch at it with a key.
Hope this is helpful

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You really need a floor grinder ! I bought an errut PRM twin disc grinder that takes 6 no carburundom blocks you will need to go over whole floor up to edge as close as you can ! Basically it looks like it's power floated and when you get laitance off it looks more like screed ! You can hire grinders at hire centres mine is quite easy to use and fairly gentle some of the single disc ones are a bit aggressive and can dig divots in the screed ! Also may be an idea to get the screed company to send the rep out to do a carbon bomb test to check RH is low enough ! I've spent a lot of times exploring this animal lol worth the time though ! Good luck Dave

 

[Flintstone]

That to me looks like it needs sanding, and I don't think anything other than diamond disk will do it

 

[Flintstone]

Have you done some moisture tests ?

 

[Dannym80]

Thanks for the replies, I've had someone out to inspect it, an old school friend in the flooring industry, who confirmed it needs sanding properly with a heavy duty copper teeth wheel or suchlike!
So that's happening later this week & get a day or 2 of not looking at tiles!

 

[Flintstone]

What about the moisture ?

 

[Dannym80]

The UFH has already been commissioned, the guy that came to remove the laitence also checked the moisture with a couple of devices. He's a commercial flooring contractor & deals with these screeds all the time so I trust him.

 

[Flintstone]

Id want to know the actual readings, rather than trust an old school friend, who might not know the requirements for tiling