wet room and anhydrite screed

[shick]

Hi

I am after some advice on the following,

I have been to look at a job which had problems in a wet room, i removed the floor tiles (very easily)
which were fixed directly to the Anhydrite underfloor heated screen.
I say its anhydrite as i have laid screeds before but this seems a lot finer and you can scratch layers of fine dust off.

What i am looking for is the correct way to reconstruct the wet room and what tried and tested materials should i use, the cost is not an issue it just needs doing correctly.

I have removed the wall tiles too as they have been fixed directly onto plasterboard and this is soaking.


I will be using hardi backer boards for the shower wall areas.

Do i need to sand the screed down (its was laid about 4 years ago) as i did read this in a thread
somewhere.

I am aware that uncoupled matting is advised, floor levels could be an issue if using ditra 25 matting, i was wondering if there was a suitable fleece membrane which would keep the door floor level difference to a minimum or am i best sticking with Ditra 25 or even durabase CI

thanks


Mark

 

[Ajax123]

Hi Mark

As it is a wet room the anhydrite should have had a fully water proof protective layer or not used. The only realistic way to deal with it will be to get it dry then apply a waterproof tanking membrane before putting the tile back down. you might be best using an Epoxy DPM once the screed is dry as this will keep the depth to a minimum and allow you to safly use a cement based adhesive. the DPM can be applied in two coats with the second being strewn with sand to make a rough textured surface to give a good key.

 

[shick]

Hi Alan

thanks for reply

Using the method you outlined above, would i need to remove the laitence from the screed ?
Can you recommend an Epoxy DPM and what sort of sand would be suitable?


I have spoken to the customer today and explained the floor level may need to be raised slightly and he was fine with this.
If i was to go down the route of removing the laitence, priming the screed, fixing ditra 25 then tiling onto the matting, what primer would i use and what adhesive to fix the Ditra 25 to the primer.
I presume its ok to use cement based adhesive to fix the tiles.

thanks

Mark

 

[Stef]

Remember if your using Hardie on the walls you will need to tank that also as it's water resistant not water proof.

 

[Dave]

Personally I would use the sheet membrane route .

Don't forget you need to be waterproofing not just the floor area but also the walls and the wall to floor transitions.

It is vital to keep the screed from any wetting and futher failures.

 

[Dave]

Just to add , Dural WP is 0.5mm thick.

 

[shick]

Cheers for the heads up on the tanking the walls guys , i had planned on that anyway but was too focused on floor preparation to mention it.


Just noticed i never mentioned the wet under floor heating Doh

Will this be ok for the dural wp or would this push me towards the ditra matting

Appreciate all advice

 

[Dave]

WP will be fine .. Ditra etc is crack mat but also tanking mat , WP will keep your height down. Or Schluter Kerdi mat if you prefer schluters products.

But Ditra is fine for the floor if you prefer to use that.. Your choice.. Just makes sure to tape/seal all joints from walls /floor to wall and floor joints and all corners.

 

[shick]

Can anyone recommend a sealer/primer for the screed prior to fixing the matting and also an adhesive for fixing the matting.

thanks