Ditra on Anhydrite

[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

 

[bugs183]

The prices are outragous, i used GBTA for a job and it worked out double the cost of cement based.

So really guys you are confirming what makes us nervous about this whole system, the cement and the gypsum are not compatible, yet we still getting specs from Bal and Mapei saying just to prime as normal, not a mention of Epoxy anywhere, change the spec and we are on very dodgy ground if there is a problem.

Gypsum based adhesives does seem the way to go, but these do not adhere as well to the tiles as modified cement based so we are back to the problems when porcelain was introduced.
There is still lots of science, and big words, but these do not make the system very inspiring confidence wise.

It just seems very blase of the adhesive companies to stick with a spec that could very easily lead to problems.

 

[Sean SML Tiling]

Ive never tiled onto this substrate but going off what you guys are sayis the method is
1-Check moisture
2-Remove film
3-hoover
4-prime using epoxy primer if using cement based adhesives
5-use gypsum based adhesive for uncoupling
6-use flexible cement based adhesive on top of uncoupling membrane

Anything ive missed out or in the wrong order?

 

[Gazzer]

Dont forget commissioning any UFH system before hand.

 

[Sean SML Tiling]

Good point.

 

[Mark S]

Smltiling, you got it + the commissioning of course
As for prices we at Gyvlon hope to launch our own brand adhesives in the near future, will advise when they are available, they will be gypsum compatible, and we will aim to be sensibly priced.
The big companies have always pushed the use of acrylic primers, but from experience there is much less risk using epoxy ones, not sure why they insist on acrylic as they all make epoxys,.

 

[Sean SML Tiling]

Id happily take a job on tomorrow without being scared I now know the process so if something fails I know it wouldn't be down to me fixing

 

[beanz]

Thanks for all the info Gents.. Very helpful!

Id happily take a job on tomorrow without being scared I now know the process so if something fails I know it wouldn't be down to me fixing

That's very easy to say, but as pointed out, the best fixing method isn't the method being recommended by a lot of the manufacturers, so if there IS a problem, i can almost guarantee it'll be on your head.

 

[Peter]

How do the gypsum adhesives deal with the fleece of the ditra? Noone will say for definite that the two won't reject each other.

 

[Ian]

How do the gypsum adhesives deal with the fleece of the ditra? Noone will say for definite that the two won't reject each other.

I haven't fixed ditra but, have fixed dural ci+ with a gypsum adhesive (creative impressions), and it stuck really well and I mean, really well!

 

[Mark S]

I am a firm believer that you should use products from 1 manufacturer, a 'system'. Ditra don't make adhesives, but are recognised as a brand leader, the 'hoover' of de-coupling membranes
If one of the major adhesive manufacturers, and I know they can, provide a spec for the full 'system' I would go with that.