Anhydrite Screed Tiling

J

J-a-m-e-s_7

Hi, I have got my kitchen extension floor to tile (6x3m). The floor is anhydrite screed which i had done about 6 weeks ago approx 40mm depth. This will be the first time i will have tiled on a gypsum based screed and after a bit of reading have come across all the possible problems (Mostly down to either bad prep, moisture content or lack of knowledge about the substrate).

I have removed the laitance using an orbital floor sander/prep machine
The tiles i am using are Grespania 600x600 Porcelain Dock

My plan is as follows:
To prime with tilemaster primer either prime+ or grip
Anhyfix to fit ditra
Then use a standard cement based adhesive from then on. Either Mapei or Weber most likely

I am wondering if this is the best route or can anyone suggest a better method as to how they would tackle it. I'm not a tiler by trade (Builder/plasterer)

Any advice would be appreciated
 
Thanks Localtiler! Is there any particular hydrometer you would recommend and what reading am i looking for? i have seen varied readings recommended by different manufactures.

My only reason for Ditra was that from what i understand the gypsum based screeds don't do well with moisture and if for example the kitchen were to flood a little then it would help prevent it reaching the screed and potentially causing further problems. If you don't think it is necessary though. I've always been a belt and braces type of guy lol
 
Thanks for the advice. Every days a school day haha. I've been working on a number of jobs recently where gypsum based liquid screeds have been used and not one of the builders knew much if anything about how to prep it or even that is was gypsum not cement based. It is all fairly knew to me too so i thought i'd do a bit of research. At least now i know the basics and have been able to point out the possible problems etc when i came across it. Also, about using gypsum based adhesive although it doesn't seem as readily available as the standard stuff.
 
If you want to use ditra as a water proofer you can but you will need to tape all the joints and seal them, it will cost a lot. I think if you get a flood to that extent you'll be claiming off your insurance anyway !
 
Honest! There's no need with Anhyfix onto Anhydrite.
They state priming is recommended simply because it won't do any harm (and it covers for dust etc, and sells more primer!) but all it does is slow down the water absorbtion from adhesive to screed, which with Anhyfix doesn't improve the final bond as it normally does with cement.

As always: if in doubt - prime it out.
All I'm saying is there is no specific need.
 
Crazy price! I can get them for about £12 on ebay. make your own box from wedi / kerdi board. Save a packet!
 
I would prime all screeds personally. I agree from a compatibility perspective anhyfix does not cause an issue but it will help act as a dust suppressant. Prime plus or similar diluted 2 or 3 to 1 with water. Leave overnight to dry and tile. No need for ditra .
 
McLovin said:
How did you get on with the unit? I am thinking of buying the same one. Just started a new thread with C/A screed issues.
Click to expand...

I decided to make my own in the end and followed the advice and it worked a treat. Think all in cost me £30 so was worth the risk. Must be a massive mark up on these units for what is really a very simple design. Will post some pictures when i get a minute
 
Firstly have you removed Laitence so floor looks like sand and cement screed opposed to the power float effect it starts with ?
If so there as previously stated no need to prime with gypsum based adheshive as it doesn't t react with screed as cement based does ! But I'd give it 1 coat 1-1 with water to stop it dusting up whilst working on it !
If you are unsure of moisture content the screed supplier can come out and do a carbon bomb test and that's final !!
The digital hygrometers aren't as accurate I've invested a lot of time and money on a floor grinder and associated kit to prepare these floors and have done quite a few up to 300m2 total ground floors ! Good luck and enjoy doing it ! Dave
 
Anyone got the link to thread about making the boxes? Think it involved routing out ? I’ve got two of the units and need to make the boxes, I don’t own a router
 
LEE MAC said:
@impish would be the man for that I think.
Click to expand...
I didn't route anything. As long as you use 10mm board, just cut (or drill) a hole to suit the stat and seal it in with something suitable.
Just make sure you don't gloop up the holes in the unit with sealant as you'll wreck the measurements.
 
Any specific dimensions required ? I’ve got some 10mm board and some ct1 I’ll get them knocked up this weekend
 
impish said:
I went at approx 12" square by 5" deep.
The important thing is making sure it's sealed up fully and then sealed to the floor fully.
Click to expand...
You must seal it to the floor using a water free system such as poly butyl tape. Don't use Silicon or decorators filler
 
I made these 3, in a hurry as you can probably tell! I've tested them along side a couple of F Ball ones and they read exactly the same. They cost about £15 each, the backs were hacked out with a router bit in a bench drill
DSC_0004.JPG
DSC_0005.JPG
 
Ajax123 said:
You must seal it to the floor using a water free system such as poly butyl tape. Don't use Silicon or decorators filler
Click to expand...

Is that because it gets a reading off the moisture in the Silicon ? Anything else you can other than the tape ?
 

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Anhydrite Screed Tiling
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