Anhydrite Screed Tiling

[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

 

[Flintstone]

Does it have heating in the screed?

 

[J-a-m-e-s_7]

No, theres no underfloor heating.

 

[Flintstone]

Imo, I would buy a hygrometer and make sure the moisture content is low enough throughout. Once you have determined that, prime with prime plus and tile with anhyfix. No need to ditra

 

[J-a-m-e-s_7]

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

 

[One Day]

Skip the priming. There is no need with Anhyfix. Just make sure the floor isn't dusty and use a wet-ish mix.

 

[J-a-m-e-s_7]

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.

 

[Flintstone]

Skip the priming. There is no need with Anhyfix. Just make sure the floor isn't dusty and use a wet-ish mix.

Prime 3 to 1 when using anhyfix.

 

[hmtiling]

I'd prime too.

 

[Flintstone]

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 !

 

[Flintstone]

You want one of the hygrometers that are a square box with a round LCD.

 

[One Day]

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.

 

[Qwerty]

Something like this is ideal.. ... ELS Digital Thermo Hygrometer « Express Liquid Screeds - http://www.expressliquidscreeds.co.uk/product/digital-thermo-hygrometer/

 

[J-a-m-e-s_7]

Something like this is ideal.. ... ELS Digital Thermo Hygrometer « Express Liquid Screeds - http://www.expressliquidscreeds.co.uk/product/digital-thermo-hygrometer/

Cheers was just looking at this one. Going to order one now. I'm sure it won't come in wrong

 

[Dumbo]

Something like this is ideal.. ... ELS Digital Thermo Hygrometer « Express Liquid Screeds - http://www.expressliquidscreeds.co.uk/product/digital-thermo-hygrometer/

Looks like mine but different colour

 

[One Day]

Crazy price! I can get them for about £12 on ebay. make your own box from wedi / kerdi board. Save a packet!

 

[One Day]

Digital Thermometer Hygrometer Panel Incubator Hatching Eggs Poultry Brooder | eBay - https://www.ebay.co.uk/p/Digital-Thermometer-Hygrometer-Panel-Incubator-Hatching-Eggs-Poultry-Brooder/1388375229?iid=200969770929

Ok, they've gone up a bit.
I got 4 of these and made my own boxes.
It's the same unit in hte ELS and F Ball boxes.

 

[McLovin]

Cheers was just looking at this one. Going to order one now. I'm sure it won't come in wrong

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.

 

[Ajax123]

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 .

 

[J-a-m-e-s_7]

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.

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

 

[Dave Mitchell]

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

 

[Flintstone]

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

 

[LM]

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

@impish would be the man for that I think.

 

[One Day]

@impish would be the man for that I think.

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.

 

[Flintstone]

Any specific dimensions required ? I’ve got some 10mm board and some ct1 I’ll get them knocked up this weekend

 

[One Day]

Any specific dimensions required ? I’ve got some 10mm board and some ct1 I’ll get them knocked up this weekend

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.

 

[Ajax123]

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.

You must seal it to the floor using a water free system such as poly butyl tape. Don't use silicone or decorators filler

 

[Dumbo]

You must seal it to the floor using a water free system such as poly butyl tape. Don't use silicone or decorators filler

Please expand and tell why .

 

[peteablard]

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

 

[Flintstone]

You must seal it to the floor using a water free system such as poly butyl tape. Don't use silicone or decorators filler

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