UFH, Drying times and Rapid setting screed - Tile Advice

[Matthew77]

hi all

I’m hoping for some technical advice on screeds and commissioning wet underfloor heating.

I went to look at at 40m2 of floor tiling job yesterday the customers would like the floor tiled before the 22nd of next month as the kitchen is being fitted then. The wet underfloor heating system is laid and the (75mm) cement based screed is being installed early next week. I’ve advised them there is no way that the screed will be dry in time to tile onto. So now the floor screeders are going to use a rapid setting floor screed I believe this is still going to be cement based.

So I understand that with a standard cement based screed it’s standard to wait 1mm per day for drying time. How does this change when using a rapid setting product as I assume although the product is rapid setting it still has a high water content until dry right?

Also regarding commissioning of the underfloor heating I understand that this must be done before Tiling and if I remember correctly the heating is taken up to full heat for a set amount of time gradually. Would someone care to explain how long after laying the screed this can be done and how long it takes?

Thanks

Matt

 

[Wishiwasatoptiler]

I'd suggest finding out exactly what the screed will made up of, get their contact details and give them a bell, then you can get the details before making any decisions on what to do next.

 

[Matthew77]

Thanks. Just waiting for the details of the screed.

Edit: it’s a quick drying dry screed.

 

[Ajax123]

To do correctly the screed should be cured for a minimum of 7 days under polythene before anything happens. Heating should not then be commissioned for a further 21 days according to bs8204. There are conflicting standards about the actual procedure for commssioning the heating but my advice is always the same I.e. switch on and run the heating at its minimum mixing valve setting or 25 degrees c whichever is lower. Leave for 3 days. Then increase by maximum 5 degrees per day via the mixing valve up to its maximum setting or maximum 55 degrees c. Leave it for 3 days. Then reverse the process before switching off for minimum 48 hours before moisture testing. Repair any cracks as required, sand and vac the screed to remove any extraneous consruction debris. If sufficiently dry then tile away. Room stats need to be disconnected as the flow temperature is the important thing. It' no good if it switches in and out during the process as that does not do it properly.

 

[Matthew77]

Thanks Alan

I figured you’d be helpful on this subject. So you are basically saying a month before the heating can be commissioned then the commissioning will take 2(ish) weeks?

Am I right in thinking that using a rapid or fast setting screed makes little or no time difference here? I’ve been told I can tile onto it a week or two after screed is laid, but from my experience it’s more to do with moisture content that setting time of the screed.

The plumber has mirrored what you have said about commissioning the heating 4 weeks after
Screed laying.

Where can I find official info on this as I’d like to be able to show customers this info as I’m sure they think I’m making this stuff up every time I tell them.

 

[Ajax123]

If it was an unheated screed you could probably tile it after 2 weeks. The basic issue is the underfloor heating which MUST be commssioned before tiling. Using a fast drying screed is unlikely to make any difference time wise. The only way really to make it quicker is to use a screed that allows the heating to be commssioned earlier. As for official documentation I will check bs8204 and see if j can copy and paste the relevant info for you.

 

[Matthew77]

Thanks again Alan
I figured it wouldn’t make much difference time wise after confirming with the plumber about commissioning times today.
A copy pasta would be very much appreciated if you can. It’d be great to have for future reference as the customers always seem to side with who ever has told them the screed is dry enough to tile on a week after it being laid rather than taking advice from the tiler.

 

[Dumbo]

Thanks again Alan
I figured it wouldn’t make much difference time wise after confirming with the plumber about commissioning times today.
A copy pasta would be very much appreciated if you can. It’d be great to have for future reference as the customers always seem to side with who ever has told them the screed is dry enough to tile on a week after it being laid rather than taking advice from the tiler.

youre last statement got that often . Dont understand why people dont listen to someone being cautious ( it doesnt financially benefit us being that way ) rather someone who just wants to take their money .

 

[Middlesex Tiles]

Can the time frame be reduced by using Durabase or similar?

I have a customer who wishes to tile asap.

 

[Dumbo]

Please correct me if somebody nows better but i think schluter claim you can tile as soon as screed is weight bearing

 

[Middlesex Tiles]

That is what I have read too - but I can't see if it is affected by the commissioning of the UFH?

 

[LM]

TOPCEM - Substrate preparation - Products for Ceramics and Stone Materials - http://www.mapei.com/GB-EN/mobile/product-detail.asp?IDMacroLinea=0&IDProdotto=207&IDTipo=1614&IDLinea=1
MAPECEM - Substrate preparation - Products for Ceramics and Stone Materials - http://www.mapei.com/GB-EN/mobile/product-detail.asp?IDMacroLinea=0&IDProdotto=201&IDTipo=1614&IDLinea=1
This is how we get round it and it works.

 

[Flintstone]

You can fast track with ditra after only a few days, but not with underfloor heating as it must be commissioned which takes time

 

[Matthew77]

You can fast track with ditra after only a few days, but not with underfloor heating as it must be commissioned which takes time

I think this is the conclusion I’ve come to. I’m going to speak to the fast set additive company Monday to confirm but they are saying it can be tiled on after 2 weeks. I’m now thinking that the screed will be dry before the heating has been commissioned! I understand the heating can start to be commissioned after 1 week of the screed being laid, then taken up in increments of 5degrees a day until at target temp then left at target temp for 3 days then gradually taken back down in increments of 5degrees a day?
Can someone confirm this is right? I’m guessing this process will take more than 2 weeks to complete, can someone with experience with underfloor heating commissioning please chip in and maybe speculate how long this process usually takes?
Thanks

Matt

 

[Flintstone]

I have a job coming up at the end of the month, which was poured Friday just gone over ufh. It’s a chemflow fast drying screed, similar situation to yours, I’ve given my advice but the screed company say they can commission the ufh after a few days, or 7 days and it will not crack, so as long as they commission it, I’m fine to dural it and tile In 3 weeks, in my opinion.