Ditra on Anhydrite

[DHTiling]

See now I am ok with cement based adhesives.
It is all in the knowledge.

 

[Ajax123]

Hey Ajax!

Quote: my personal opinion is that you should avoid cement based adhesives on the screed and use a gypsum compatible adhesive to stick down the membrane. Then use a flexible cement based addy to stick the tiles to the mat.

This is the first time i seen any screed rep actually recommend this method, is this now common theory for these screeds for applying an uncoulping membrane, or just your personal opinion, i was uncertain as to the stance companies such as Schluter take on it, but i've always thought it was the best overall solution. The gypsum is compatible with the screed and the cement above is compatible with the tiles, especially porcelain.
I always uncouple over under floor heated screeds, wether stone or porcelain, i've seen 20mm thick stone broken by movement in doorways where the customer/builder refused to install control joints or use an uncoulpling membrane.

That method will satisfy the tilers, now we just need to get the screeders to put the expansion joints in the doorways as required, i've tiled a number of these screeds and not seen any joints added between doorways ever!!

-

no it's not common theory but if its a heated screed and its travertine the British standard recommends uncoupling regardless of the screed type.

 

[bugs183]

I'm aware of the travertine side of things, thats a given. I meant the actual use of gypsum based adhesive with n uncoupling membrane.

 

[Ajax123]

I'm aware of the travertine side of things, thats a given. I meant the actual use of gypsum based adhesive with n uncoupling membrane.

Ah right. Well no that is a personal opinion based on technical appraisal and experience tinged with a dose of common sense.

 

[bugs183]

Ah right. Well no that is a personal opinion based on technical appraisal and experience tinged with a dose of common sense.

Your quite right!
It's a shame we can't get Schluter to go along with it as well, it would make all this much better for everyone!!!
Anyway, pub time!

 

[The D]

Bugs, of course test for moisture, its sometimes taken it for granted that this is a standard procedure.
Not a problem the questions being asked, I'd rather someone asks than plows straight in regardless.
There is a lot of development work going on to make gypsum compatibile adhesives, levellers etc, as these are launched etc we will put the info/data sheets on the forum.
I would much rather people understood and felt happier about tiling on anhydrite screeds

So are you saying that the adhesives we use every day are not compatible ?????????????

 

[Ajax123]

So are you saying that the adhesives we use every day are not compatible ?????????????

Chemically speaking yes. Cement which is your everyday adhesive is n compatible for direct contact with gypsum. In order to manage this incompatibility you must use a primer. Trouble is the primers don't always get applied in suh a way as to be effective (evn when following manufacturers instructions I might add). Often the primers are lilies or water sensitive so if any moisture gets into the system I cn cause emulsification f the primer. If ou use cement based adhesives my recomendation would lay be I use n epoxy primer. Better still though remove n element of risk by getting rid of the primer and using gypsum compatible adhesive that an be used primer free. (Some cannot)

 

[Sean SML Tiling]

Chemically speaking yes. Cement which is your everyday adhesive is n compatible for direct contact with gypsum. In order to manage this incompatibility you must use a primer. Trouble is the primers don't always get applied in suh a way as to be effective (evn when following manufacturers instructions I might add). Often the primers are lilies or water sensitive so if any moisture gets into the system I cn cause emulsification f the primer. If ou use cement based adhesives my recomendation would lay be I use n epoxy primer. Better still though remove n element of risk by getting rid of the primer and using gypsum compatible adhesive that an be used primer free. (Some cannot)

Threads like these are excellent, so much knowledge is gained by just reading and understanding what is being said. Fair play ajax you know your stuff. Why dont u write a thread of exactly how to prep a anhydrate screed in the forum arms?

 

[Mark S]

Bang on Ajax, some water based acrylic primers are more susceptible to moisture and completely disappear or as you say emulsify, epoxy every time to create a barrier between gypsum and cement.
There needs to be more gypsum compatible adhesives /levellers on the market.

 

[DHTiling]

And better prices mark 🙂