Limestone onto liquid screed before it's fully dried?

[ashthekid]

Hi,

 

I've been told that even though it's been over 3 weeks since my liquid screed was poured it will be ok to lay the limestone floor because they are using an anti-cracking matting down 1st. Is this true?

 

Also, if this matting is being laid do I still need to prime the screed layer or is that a waste of time?

My logic is that it's not having adhesive directly onto the screed anymore so why need it?

 

 

[Nickfromwales]

Have you spoken to the tiler about sequencing?

The decoupling membrane certainly does get laid with tile adhesive, so how do you think it doesn’t?

Is there a laitance on top of the liquid screed that needs to be mechanically scrubbed off? Do you know if it was a cementitious screed ( Flocrete ) or a Gypsum based screed?

[ashthekid]

It’s a Gyvlon screed and the laitance has been removed mechanically 7 days after the pouring on 1st July. 
The tiling company laying the limestone floor has said they could lay it now if I wanted because of the anti-cracking membrane going down bit I am very undecided and cautious about this. 
I have a digital hygrometer attached to a too. Which is likely to take the longest to dry and it’s currently reading 95% RH and room temp of 20 degrees. 
I plan to get a dehumidifier or two today to help. Assuming I should really only switch these on overnight when all the doors and windows are closed?

[Jilly]

My plumber advised against a decoupling membrane as it can reduce the efficiency of the floor. This does make sense, so we waited til we were very sure it was dry before laying and indeed it does warm up quite quickly on a low heat. People often use these mats to avoid cracking as no one wants to take the risk. Do plenty of research and see how you feel about the pros and cons. Also don't be tempted to turn the floor up to dry it quickly as that will crack it. 

[ashthekid]

Yeah it’s a difficult decision to make. 
I have a digital hygrometer attached and sealed to the screed and it’s currently showing 95% RH levels which is confusing me a bit as I would have assumed after some amazing hot weather with all the doors and windows open that the screed would have majority dried by now. 

[Temp]

Does the screed and will the stone run through doorways? Without an expansion gap this can happen..

 

[ashthekid]

Yes I have quite a few doorways it runs through. There is one long run of about 40meters. 
 

But that crack wasn’t caused by not dry enough screed was it?

 

Edited July 28, 2022 by ashthekid

[ashthekid]

Well I’m a couple more weeks further into my drying period and so far we’ve had pretty impressive dry sunny weather so I’ve had all the windows and doors open to ventilate the place fully but I’ve also used a dehumifier constantly too. 
so far the digital hygrometer is still showing 95% RH which is crazy if you ask me. Something must be clearly wrong with it surely. 
 

I reckon I have approx 40-50mm of screed. Surely over 6 weeks of 99% dry weather as well as dehumidifier would have done the trick!
 

[Russell griffiths]

Why measure rh surely you need to measure moisture content of the screed. 

[Conor]

As Russel alludes to, the humidity in the air will remain high as long as there is moisture in the screed. Our air humidity didn't drop until moisture levels in the screed dropped below 10%.

[Roundtuit]

14 hours ago, ashthekid said:

I reckon I have approx 40-50mm of screed. Surely over 6 weeks of 99% dry weather as well as dehumidifier would have done the trick!

 

Even my lawn is dry enough to tile now.  95% RH can't be right can it? Have you got plastering drying out too?  

 

[ashthekid]

Plastering was all done, dried out and painted before the screed even went down so there’s definitely been no other factors affecting it’s drying. 

 

I’m just getting a bit concerned now as the stone floor is being laid from the 15th Aug which will be almost 7 weeks which I would have guess was more than enough time. 
 

I suppose the 2mm anti-cracking membrane going down on top of the screed will help in some to alleviate any moisture risks. 

[Jilly]

Maybe get another meter or two to compare? The reading on my dehumidifier started to be consistently about 20 points wrong a while back. It might need the filter changing...

[PeterW]

An air RH meter won’t read the screed moisture content. You need a probe meter for that… you’re basically measuring the moisture content of the air just above the floor. If you’re at 7 weeks just crack on and lay the floor. Don’t forget to make them do full bed and seal the backs if its limestone.