Travertine on Anhydrite screed

[smallholder]

Having read many posts on anhydrite screed I am totally confused.

We have a 5x6m screed floor to tille with travertine. The travertine is unfilled with minimal holes 12mm thick and various sizes (opus pattern).

The screed is 55mm thick and has been down for 90 days now. It has been heated using warm water ufh for approximately 3 weeks of that time together with a dehumidifier since day20 or so.

The screed is Gyvlon which i was told is low laitance. I have sanded the surface to create a key!

I was thinking of either using a gypsum based adhesive directly onto the anhydite with no decoupling membrane or prime the screed then use a cement based adhesive with dural durabase ci decoupling membrane. Your views would be most welcome.

 

[Spud]

I would use ditra and cement based adhesive

 

[Gazzer]

I would use ditra and cement based adhesive

Just make sure you prime well .

 

[DHTiling]

I would use ditra and cement based adhesive

Snap!! .. same here...

 

[Ajax123]

Having read many posts on anhydrite screed I am totally confused.

We have a 5x6m screed floor to tille with travertine. The travertine is unfilled with minimal holes 12mm thick and various sizes (opus pattern).

The screed is 55mm thick and has been down for 90 days now. It has been heated using warm water ufh for approximately 3 weeks of that time together with a dehumidifier since day20 or so.

The screed is Gyvlon which i was told is low laitance. I have sanded the surface to create a key!

I was thinking of either using a gypsum based adhesive directly onto the anhydite with no decoupling membrane or prime the screed then use a cement based adhesive with dural durabase ci decoupling membrane. Your views would be most welcome.

Travertine on heated screed of any type should be uncoupled (bs5328) which really makes the use of an uncoupling membrane essential. 90 days at 55mm may not be long enough depending on temperatures etc although it probably will be. A moisture test will determine this. Use a hygrometer (needs to be below 75%), a carbide bomb (below 0.3%), or an oven dried sample .... The screed supplier may be able to do this for you although I do not know for sure.

From the floor coverings point of view low laitence is largely irrelevant as the screed still requires light abrasion (which you have correctly done)

you could use a gypsum adhesive such as GBTA from creative impressions or similar having primed the screed first with an acrylic primer or alternatively once determined dry you can use a flexible cement based adhesive although correct priming is essential. It will depend n which adhesive you select as to what the most appropriate primer is but the best chance of success in combatting the chemical reaction between screed and adhesive would be achieved using a water dispersion epoxy primer such as screed master epoxy from laybond.

The alternative to sticking it down with tile adhesive would be to use vinyl adhesive. I have seen this done a few times but have no real experience so a call to the likes of ardex or f ball and co would be appropriate. If you use an acrylic pressure sensitive adhesive you would be safe to use an acrylic primer rather than epoxy.

once the uncoupling membrane is down use a flexible cement based adhesive (white of course) to stick your trav down.

In terms of underfloor heating make sure you have run it through a full temperature cycle (up to and down from maximum operating temperature) before doing anything and make sure you vacuum it before you prime.

hope this helps.

 

[smallholder]

Just make sure you prime well .

From comments on the forum epoxy primer is the way to go but where is the best place to get it from and how much will it set me back. The floor is 31sq m.

Many thanks for the messages so far.

 

[Ajax123]

Laybond Bostik screed master epoxy (make sure its this one)
tremco illbruck cs epoxy
merlin coatings Merlin barrier coat

contact numbers are all on line on their websites.

1unit is about £45 ish last time I priced it and will do about 100m2 from memory.

 

[Mark S]

Hi,
You seem to have been given advice from the forum members,
As manufacturers of the Gyvlon binder we would echo the points given.
You have correctly lightly sanded the foor to give a good key, not to be confused with actually removing a laitent skin.
Your tiler should be able to test the floor for moisture I would recommend a hygrometer or the carbide bomb method. The heating commissioning cycle coupled with the de-humidifiers will ahve removed most of the moisture but still test.
As for the adhesive, the choice is yours, prime and cement based, or a gypsum based.
The GBTA from Creative Impressions is well liked, Kerakoll do H40 Ideal (standard set)
There are various de-coupling membranes about, but my advice would be if possible to use the 1 manufacturer for the lot
Mark S
Technical and Specification Manager, Gyvlon UK