What went wrong...?

[zoemac]

Hello folks I need some help.

At the start of December 2013 I had a Tarmac Tru Flo Screed floor laid over underfloor heating. I believe this is a gyvlon/gypsom/anhydrite screed.

I wanted to tile on the floor and was given advice by the screed company that either a Gypsom based adhesive was needed or if we wanted to use a cement based adhesive we would need to seal the floor well.

The floor was kept above 5 degrees c and was left to dry naturally until the mid Feb when the underfloor heating was switched on just to make sure it was dry.

The floor was swept and hoovered to remove any surface residue and dust and the my builder applied numerous coats of SBR primer to seal the floor.

The floor was then tiled with porcelain tiles using BAL Rapidset flexible. We didn't use the underfloor heating again till end of March to give the floor the chance to dry naturally (and because we were still working on other parts of the house and not actually living there)

The problem that I have is that all the tiles are lifting. I first noticed this in April 2014 and it has got worse and worse. Tonight we took up a couple of tiles and the adhesive is stuck really well to the tiles, but does not seem to be bonded to the screed. I am aware that there can be a reaction between the Gypsum Screed and the Cement based tile adhesive but the advice we were given was that this would not happen if the floor was well sealed.

What has gone wrong?

My builder came to take a look tonight and basically he thinks we need to re-lay the whole floor, and because the adhesive is so well bonded to the tiles we will not be able to re-use them. Its a BIG room so this will cost me a fortune - and I really can't afford to do this. What can I do??? Help please.

 

[Dougs Third Go]

sounds to me as though it could be laitence, was the floor sanded before sweeping/hoovering/priming?

 

[Gazzer]

As Doug says, the laitance should have been removed and hoovered up . have you removed a tile and if so what does the floor look like beneath and what does the adhesive on the tile look like?

 

[zoemac]

Thanks Doug. I did a bit of research before I got the floor laid. I believe there are a couple of different flow screed products. The one we used was Tarmac Tru Flow which I believe is slightly different from the Lafarge flow screed. The supplier told us that the tarmac one would not need sanding, it formed a thin crust which just needed to be removed by sweeping. I have double checked the data sheets we were sent at the time and they confirm this. I believe the LaFarge product forms a really tough shiny crystalline layer which needs to be sanded.

 

[CJ]

Also, it should have been an acrylic primer. 1st coat diluted, 2nd coat neat, but as mentioned above, if it wasn't laitence free, and thoroughly hoovered.......you were always going to have a problem.

It does sound like another "Builder error"

 

[Ajax123]

There's a good chance it was not dry. Natural drying would need around 20 degrees and 60% rh. The choice of adhesive puts you at risk and whilst SBR can be used it is sensitive to moisture as well. Sanding the floor to remove Laitance and any other surface detritus is essential for correct preparation. If the tiles are coming up clean it is a printer failure as that is the bit that is supposed to stick to the screed and the adhesive sticks to that in turn. You will need to lift the tiles and replace them. I would use a gypsum based adhesive. There are loads about and they are no more expensive than cement based these days.

 

[zoemac]

Sorry - as you will guess I am not all that clued up. The laitance is the layer that formed on top of the screed, yes? We definitely removed all of this - it didn't need sanding, came up easily as we brushed with a stiff brush. This is what we were told to expect by the screed people.

Yep - have removed a couple of tiles (didn't take much effort!) - the adhesive seems well bonded to the tile but not to the floor. The adhesive looked pale, chalky and was very brittle. There was still signs of the SBR on the floor. I'll take some pictures later on and post them here.

Again I'm really grateful for your help as I am clueless as to what could have gone wrong.

 

[zoemac]

Showing my stupidity no doubt - is SBR not an acrylic primer?

 

[The D]

who decided the floor was dry and did they test it or was it just that surfactant time had passed so the floor must be dry

 

[Ajax123]

who decided the floor was dry and did they test it or was it just that surfactant time had passed so the floor must be dry

I suspect no test was carried out but won't pre empt...