How ? Cement based TERRAZZO on a calcium sulphate screed.......

[DHTiling]

The issue is keeping the wetting from the screed.. this is why i say prep is crucial.. The only way i would say to protect it is to epoxy sealer the surface.. but i have not done this before on an Anhydrite screed or laid terrazzo over one.. so your best bet is to contact Ajax123 on here who is the technical specifications guy for Gyvlon...

 

[fergal]

Would a good Acrylic primer do if it was done with two coats ,first 1-1 and the second neat,if we are doing a cement based leveling compound this is what we use and never have any problems with it.

Maybe the guy doing the Terrazzo would have to change his mix to allow for him changing the way he normaly works.ie not being able to wet up the sand and cement screed he usually lays on....

 

[DHTiling]

Only method after priming i would say will give a better bond is to slurry coat before laying terrazzo.. but check with Alan first.. as these screeds are his speciality..

 

[DHTiling]

You can pm him here or await his arrival..🙂 Ajax123

 

[Ajax123]

this one is a little tricky as I am not familiar with Terazzo being laid this way. The only terrazo I have seen is done the old fashioned pressed wet bed method into fresh sand cement screed.

In terms of prep of the screed however if you are using a cement based adhesive I would always prefer a water dispersible epoxy primer as these act as a much more robust barrier to the migration of moisture borne sulphates which tend to be responsibl for the Ettringite delamination events. As you have the old fashioned stuff and have taken off the skin getting the epoxy into the screed would not be a problem as it can be on the newer low laitance screeds. I wonder if you might be better speaking to one of the gypsum based adhesive suppliers. Are you in Ireland by any chance Fergal. Laying the cement based levelling compound is the same as laying the cement based adhesive in terms of chemical incompatibility and I would always receomnd Gypsum levelling in preference to cement if possible. The heating MUST have been commissioned and run (it sounds like this has been done) The moisture sounds a bit borderline at 0.48%. I would probably be inclined to run the heating for another few days just to force out a little more moisture. I realise the general recomendations in terms of moisture but if you are using cement addy or leveller I would aim for about 0.3% moisture using the CM method.

 

[The Legend; Phil Hobson RIP]

Hi Fergal, and:welcome: I presume by your term,( insitu terrazzo) you mean mixed on site and laid insitu, as in on site, not preformed terrazzo tile? Being rolled, and then polished? as in the old way

 

[fergal]

My description of in situ Terrazzo is as you say AJAX123, the pressed wet bed method, only this time it's not a fresh sand and cement screed.The client wants the faster heat responce time of the Gyvlon thats why he went for under floor heating. But the clients wife wants a Terrazzo floor and she has been told that the cement based Terrazzo is the best on the market.

I would like to know is this possible on a gyvlon screed and if anyone has done it before and are able to give me a few pointers.

On a few occasions before we have done a heated Gyvlon screed,primer it and then placed a sand and cement screed on top fixing the stone tile's direct on to the fresh screed.Would this be something like the process of putting down an insitu Terrazzo as i have never actually seen one being done?

 

[Ajax123]

My description of in situ Terrazzo is as you say AJAX123, the pressed wet bed method, only this time it's not a fresh sand and cement screed.The client wants the faster heat responce time of the Gyvlon thats why he went for under floor heating. But the clients wife wants a Terrazzo floor and she has been told that the cement based Terrazzo is the best on the market.

I would like to know is this possible on a gyvlon screed and if anyone has done it before and are able to give me a few pointers.

On a few occasions before we have done a heated Gyvlon screed,primer it and then placed a sand and cement screed on top fixing the stone tile's direct on to the fresh screed.Would this be something like the process of putting down an insitu Terrazzo as i have never actually seen one being done?

You could overlay the Gyvlon screed with a sand cement screed and press the terrazzo into this yes. I have seen this done with various tle types over Gyvlon. Typically the sand cement bed would be around 45 to 50mm deep so it would actually increase the depth of the floor which would have an inevitable effect on the mass of the floor thus affecting the response times for the underfloor heating system. The underfloor heating should still have been comissioned prior to overlaying and then I would coat the screed with a couple of coats of Acrylic Primer. There may be some chemical reaction at the interface between the two screeds but as the sand cement would be pretty deep I don't see this as a major issue. The alternative would be to use water dispersible epoxy primer which would completely remove any chemical reaction risks.

Clearly you would not be able to press the tiles into the Gyvlon screed but I guess that is stating the obvious (at last I hope so - LOL) Are there no other tiles on the market which mimic Terrazzo which you could install with a standard adhesive......

Thinking about it though is there a pourable thick bed adhesive that you could use....not sure but perhaps the pro tilers on here might be able to say.
Also you seem to be saying that you have not done the wet bed method - is this something you should be taking on if that is the case or have I misunderstood your last comment.