Anydrite Screed / wetroom questions

[Julian Power]

Hi, I would appreciate any thoughts on a few diverse questions on a singly storey barn project we are doing.
- I haven't used anhydrite liquid screed before. I understand it needs roughing up 5 days or so after laying to help it dry and for adhesives to work. I will check with manufacturers re correct adhesives working with it ok. Any experiences good or bad?
- However, in 2 x wetrooms I really don't want to put sheet membrane down (will use former trays for showers). They are smallish so would be easy to paint a liquid membrane. However will this stick to the anhydrite ok? Should I seal / prime the before the liquid membrane? If so what products work together etc (could be primer, then liquid membrane then adhesive so don't want anything coming apart over time / with any moisture getting in). Any experience on this gratefully received.
- I was going to use no more ply around the shower area and then tape and seal the joints only, rest of walls we will use green plasterboard. Obviously will tape and seal around the former and up to the walls as per instructions.
- The screed is only 40-50mm. Plan is to fit shower drain in insulation, lay & glue (what glue/sticky is best?) some oversized 18mm ply on the insulation (correct hole for drains cut in it), fix through the insulation to the slab below so it is rock solid. Then we will block out the tray area and we can pour the screed (with edges of ply being under screed where oversized). Then stick the former to the ply with adhesive (any issues here?). If we get the levels right should be then be flush with screed around it. Sound sensible?
Few issues are the ply will be proud of the insulation so around the edges where oversized may only have 25mm of screed over it.
I have these foam former trays that make me a touch nervous so they need to be fixed rock solid.
Thanks in advance!

 

[hmtiling]

Angela reason you don't want to use a membrane on the floor? Impey waterguard after priming with Bal apd would be my choice

 

[Old Mod]

Anhydride screeds are very moisture sensitive, and shouldn’t be used in wet areas.
A membrane is a far safer choice than paint on tanking.
Membranes are on average only 1mm thick, it won’t cause height issues.

 

[Dumbo]

As @hmtiling impey membrane is the only thing I would consider for the reasons @3_fall said

 

[Julian Power]

Thanks. Is Impey Waterguard really worth the money? The Mira system is about 1/4 of the cost.

 

[Old Mod]

There are a number of waterproof membranes available, all work. Some are easier to install than others.
And it’s all about the install.
Get that wrong, and you just might not as well have bothered.

 

[Ajax123]

Hi Guildford contracts. If you want to give me a call on Monday I can tell you through the entire process properly. It sounds like you have already been given some snippets of incorrect advice I terms of roughing up and this helping the screed to dry both of which are technically inaccurate. I can also draw you up an NBS specification and point you toward decent quality screeders. Up to you 07966651006

 

[Qwerty]

Have you decided what former you will use?

 

[Julian Power]

The formers we have are aquafix, extruded polystyrene from PureAdhesion. Following feedback above I was then going to use a Mira Tanking kit membrane on the floor around the former.

 

[Old Mod]

Alan (Ajax ) is correct tho, the information you have on preparation is at best poor.
With the amount of information you need to digest, I would recommend you take him up on his offer of a phone call.
I’m sure we’d of covered it eventually, but a one to one with Alan, will be a much faster route.

 

[Ajax123]

Offer is open 3fall....

 

[Julian Power]

Thanks everyone. I have spoken to the screed manufacturer technical dept, so much clearer. Interestingly I was told water is only a problem if it anhydrite is wet all the time..... Will try Ajax123 again today. Thanks