Tiling onto calcium based screed

[Mitch2610]

sorry to repost ages later in my thread, I did find out it is definitely a sand and cement floor which is why it’s so thick, had to be a minimum of 75mm. It’s been 7 weeks since pouring now and I’m ready to floor tile next week. I have a digital hygrometer on it as well as we speak, it’s been 10 hours, started at 71% and it’s been at 79% for perhaps the last 3 hours so can’t see it going up again now but will check in the morning. What’s everyone opinions as 75% is what I’ve read it should be? Would you risk it being a little higher? I have a dehumidifier so going to get that going 24/7 for the next week after I’ve taken the tester up.

Cheers

 

[Dave]

Are you crack matting as well. ?

 

[Mitch2610]

Are you crack matting as well. ?

Yes got kerrakoll primer A, biogel no limits and the anti crack mat they do

 

[Dave]

Is it the green pro matt.

 

[Mitch2610]

Is it the green pro matt.

I haven’t actually got it yet but it’s just called kerrakoll biotex anti fracture mat

 

[Ajax123]

if the crack mat is a moisture stabiliser like ditra youll be fine togo ahead. For info the floor should be 80% to be considered dry but there is an error built into the test regime so has a tolerance of minus 5% hence 75%. for equilibrium you should have two consecurive readings the same 4 hours apart. so based on your tests its not in iequilibrium yet. that could be to do with the changability of the site conditions this time of year.

 

[Mitch2610]

if the crack mat is a moisture stabiliser like ditra youll be fine togo ahead. For info the floor should be 80% to be considered dry but there is an error built into the test regime so has a tolerance of minus 5% hence 75%. for equilibrium you should have two consecurive readings the same 4 hours apart. so based on your tests its not in iequilibrium yet. that could be to do with the changability of the site conditions this time of year.

Thanks for the info it’s helpful to know, so after 4 hours it was 74% but this morning after 24 hours it was at 83% so my question is will a product like DITRA be able to cope with that if needed at all?

 

[Ajax123]

ditra would cope. I would not necessarily trust the hygrometer reading this time of year simply because the temperatures overnight tend to lead to interstitial condensation issues which throws the readings off.

 

[Dave]

I haven’t actually got it yet but it’s just called kerrakoll biotex anti fracture mat

The green matting is a vapour equalisation one. So my advice is use that or any other similar matting , my preference is Ditra.

 

[Andrew Owens]

The Kerakoll Biotex matting can only be used on thoroughly dried out screeds, you will need use Ditra matting or similar.

 

[Mitch2610]

Thanks for the advice, think I’ll go for DITRA or the Kerrakoll equivalent then, what about the adhesive can I still use Kerrakoll biogel or would I need a different adhesive to put the matting on top of? And where would you apply the primer? I think my tiler would know this but just want the advice for my own benefit and peace of mind