Latex screed is cracking.

I've just laid a latex screed over electric matt underfloor heating (about 8-10 mm). The matt sits on top of insulation boards (10mm), which in turn sits on top of a concrete floor).

The latex screed has cracked in multiple places and if I press hard with my foot, I'm not certain, but I think I see slight verticle movement.

Am I safe to tile on top of this? Tiles are 10mm thick stonker tiles (600mmX400mm)?

What laytex did you use?

Is the insulation stuck to the concrete or loose laid?

Has the heating matt been turned on?

Few more details will help, also what adhesive & grout do you propose to use and are the tiles ceramic, porcelain or natural stone?


8-10mm is more than you need for a heating matt, you only need to just cover the wires so about 4mm is usually adequate, who's matt was it.

JAson

The insulation was loose laid and are EkoBOARDs .

The heating matt has not been turned on (not wired up yet).

The tiles are Stonker (ceramic porcelain mix) and are rated for outside use (I think they are pretty tough).

The grout will be flexible and I will mix it with a further flexible additive.

Not sure what adhesive (bought from porcelanosa - they supply the tiles).

Not sure what latex was used, as the builder choose it.

Not used that particular board but all the others I have used have been stuck down with tile adhesive. It looks very similar to Easy-heat boards which I have used a few times.

Looking at the ecoboard site this is what they show as well so you have not followed the instructions. The boards are moving about under the laytex due to them not being fully supported.

No easy answer short of ripping it all up and starting again

Did you tell porcelanosa that you were laying onto UFH as the adhesive will be different to what they would have supplied if you said it was a concrete floor. Likewise did the builder use a laytex suitable for UFH. Hope the mats were tested before you laytexed them and the readings noted.

Jason

No and no. The builder was aware of the underfloor heating, but I'd be amazed if that made a difference to his choice of screed (cheapest wikes had to offer no doubt). I'll certainly check with the tile supplier on the cement however.

I bought the insulation boards from uheat of the phone and asked if they needed cementing and got an answer in the negative. But there's no point in going down that road. I'm learning hard lessons on this build - don't rely on the builder and do all the research yourself (a number of times it's been apparent that the trades men are 'winging it').

I think I'm gonna to tile the floor and see what happens (gone to far down the road now - kitchens going in). Flexible cement, flexible grout and all fingers crossed.

Thanks for your help. Much appreciated.

I would not tile the floor until you are sure that the floor/sub floor is stable. Listen to Jasonb's advice.

We would always fix these type of boards to the floor never loose lay.
The underfloor heating does not want to be turned on for at least 3-4 weeks then warm up gradually.

Make sure you use a single part flexible adhesive and grout when you fix the tiles.