concrete curing under tiles over underfloor heating

[rhead]

So theres a damp membrane/120mm slab thats going to have insulation then underfloor plastic heating pipes fixed in a grid, this is all contained within a brick wall. What I cant work out is the cure time for the 60mm screed. As soon as the heating is switched on all water will leave, and the cure is finished. The recomended cure is 28 days in one place and 1mm per day in another. Can I tile before the heat has been switched on or will this have an adverse affect to their bonding and or the cure.

[darrenba]

I've been always advised to allow 1mm/day to fully cure and not use the underfloor heating or cover it until it has done so.

[rhead]

So Ive got another dilemma now, if I use a cement based adhesive with a cure time, rather than a dispersion time as for ready mixed could I tile on curing screed or do you think I shall be blocking the exit of water. Cause as soon as the heating is switched on all water will rapidly leave one way or another. Or should I wait between screed/self leveling and adhesive. Its just CURE is water dependant not exit of water dependant.

[royaloakcarpentry]

You can't just whack the heating on full blast to ''cure'' the concrete and screed.

I rarely us Bal products however the BAL Green Star Screed can be applied 24 hours after screeding has been laid. This is a powdered adhesive.

I would call the BAL technical help line as I am not sure if this can be used with a piped under floor heating system.

[rhead]

Will get on to them in the morning, and post the reply.

[royaloakcarpentry]

Thanks for putting reply on here.......I don't use BAL products so will be handy to know.

I use nicobond products but they don't do one for use on new screed. It has to have had drying out time.

[rhead]

All phone lines were busy so Ive sent them an email, as soon as I get a reply I will post.

[rhead]

Ive lifted below off Bal web site

How long should cement:sand screed be left before tiling?

3 weeks for Portland cement (including 7 days cure + 2 weeks continuous drying out in air) or 24 hours for screeds incorporating BAL Quickset Cement.
If not possible to allow Portland cement:sand screed to dry for 3 weeks, allow min. 24 hours for drying, then tile using BAL Green Screed Adhesive.

How to tile over heated screed?

See page 15 of the BAL Sitework Guidance literature for base preparation details.
Then fix tiles with 3-6mm bed of BAL Single Part Flexible or BAL Rapidset Flexible. When dry, grout with (min. 3mm joint) BAL Superflex Wide Joint Grout - or BAL Wide Joint Grout with addition of BAL Admix GT1 (diluted 1:2 with water) or BAL Microcolour Wide Joint Grout.

As Im not worthy of access to Page 15 this is as far as I got.

[rhead]

Dave from Bal technical advice says:-

Because you are adding the heating element you should commission the heating first. IE screed it, wait 5 days for it to go off (using Quick Drying) then switch on heating, let it come up to temperature and run for a while (48 hours) before you switch it off, let it cool completely and then, finally, tile it.

Sounds good to me, any body got any reservations on any aspect of the job as a whole.

[royaloakcarpentry]

Yes, obviously forget what I said about BAL greenstar screed adhesive, even though I said I was unsure if it could be used with underfloor heating.

You did the right thing calling them, this is what I would have had to do anyway.

There are one maybe two tilers who come in that would have the knowledge in their heads, but they do not always pop on.

Use the products which they have told you. I would commission the heating slowly. So introduce it up to full temperature over the course of a couple of days before leaving it on for 48 hours. Start the heat off on Monday, off on Friday and then start to tile on the Monday.

[rhead]

I agree with you about increasing the heat slowly Ive seen too many cracks appear in concrete. It does now mean you can give the option of under floor heating and re tile in 2wks. Maybe thats what this sort of heating has been waiting for to gain popularity. Thanks for your input. Brian

[Battman]

You'd be Mad to tile straight onto the screen within 8 weeks of laying new screed and turning on the underfloor heating is just asking for trouble! The screed wil crack and/or turn to sand but there is a fool proof easy way to tile on the screed within a couple of days use Schluter Ditra matting, it looks a bit like bubble wrap and is called a de coupling membrane and is used on commercial jobs when they don't have 8 weeks to wait for the floor slab/screed to dry. It allows the sub base to have a limited amount of movement without transferring it to the tiles.
Comes on a roll 1m wide to the length you need most good tiling stores sell it now

[Battman]

P.S Before you all moan saying 8 weeks! Rubbish.
Read the Tile manufactures guidelines! Because when the screed cracks and takes the tiles with it you have no comeback!
8 weeks is also the stated times in the British Standards.
The de coupling mattings great lay it, tile it job done never any comeback or warranty issues in over 5 years of using it.

[rhead]

Ive just read about the sheeting and it sounds good stuff, any tips for using it under a ceramic tiled shower base.

[thescruff]

Agree with battman, you'd be mad to put the underfloor heating on before the screed is properly cured.