Limestone Discolouration - Tile Advice

[Fraser Tiling]

Hello guys,
just fixed 20 metres of 15mm 900x600 tumbled limestone to a screeded floor with underfloor heating using Ultra extended set white flexible adhesive.
When I returned to seal the tiles there was a noticible discolouring to the tiles which I put down to the moisture still coming through the stone.
They were laid three weeks ago and the underfloor heating was turned on a week ago but the tiles still dont seem to be drying to a uniform colour.
I have laid similiar tiles before with the same adhesive and havent had this problem.
Instarmac have seen photos of the tiles and say the floor needs more time to dry and eventually the floor will dry, but Im worried about the tiles being stained by the moisture.
Anyone have any experience with this problem or any advise?

 

[Tile Shop]

What type of screed is it and how thick?
How long before tiling was the screed laid?
How wide are those grout joints? (from the images they look to small for limestone with UFH and no uncoupling)

 

[Fraser Tiling]

standard sharp sand cement screed, laid on 12 of december so plenty of time to dry, only a 2-3mm joint but not had problems before with a tight joint on antique edged tile

 

[One Day]

Extended set adhesive with white limestone. I think the word "extended" is the problem.

 

[Fraser Tiling]

Extended set adhesive with white limestone. I think the word "extended" is the problem.

agreed, wont be using extended set adhesive again with stone, although states on the bag its suitable for natural stone, manufacturers claim it will dry eventually but im concerned it may stain or discolour the tiles

 

[Ian]

Was the stone back skimmed or just adhesive troweled onto the floor?

 

[Tile seller]

I can only think that this is due to using the Extended open time adhesive.
I received a technical bulletin only a few weeks ago regarding using only fast set with natural stone, although never had much of a problem before.
If you've not sealed it yet then best to wait and hope it does dry out first.
People complain about porcelain being hard but, you don't get these sorts of issues with it.

 

[Just Rizzle]

standard sharp sand cement screed, laid on 12 of december so plenty of time to dry, only a 2-3mm joint but not had problems before with a tight joint on antique edged tile

what makes u sure it had plenty of time to dry did u moisture test it.
my take on the photosis moisture rising up through the floor.
can you take a small cut one up and test the floor. you might find moisture trapped under the tile
you can see your trowl marks through them was it a 12mm trowel

 

[Fraser Tiling]

no, I didnt skim the back of the tile, used a 12mm notched trowel on a shallow bed, some of the tiles were back buttered to adjust heights, hence in places you can see trowel marks coming through, once again although not text book, have been laying stone for twenty years and never seen anything like this before.
The screed looked a uniform colour, and didnt appear to be damp although the floor was very cold, i also tiled a raised metal "manhole" cover, although very deep bed, it also is discoloured.
I havent sealed the floor for obvious reasons.
My main concerns are whether the tiles are going to stain, trowel marks, will eventually disappear, and I think the extended setting adhesive is clearly the main culprit, perhaps a wider joint may of helped the drying process, and cold temperatures wouldnt of helped either.
Im reluctant to use any cleaning products such as Power Clean or add any more moisture to the floor as suggested by some local tilers.
The UFH has been on for 6 days now, and is upto 21 degrees, and as expected there been little to no change in colour, hopefully this is a good sign that the moisture is being forced up and out of the stone, and within a short time the tiles will dry.

 

[Chalker]

The underfloor should have been commisioned before tiling. I'm pretty sure this is the moisture from the screed trying to get out.

 

[One Day]

Back home now and had a closer look. I didn't pick up on the uncommisioned ufh part.
I'd say that it's primarily the additional moisture of the extended set not yet gone, and in part - moisture rising from the screed still.
Good sign is the dryness around the grout joints. I think this will dry out but could take quite some time yet...

For future - please use Ditra and a rapidset. That would mean you could fix safely onto uncommissioned heated screed and no risk of residual moisture lurking in the adhesive.

 

[White Room]

Was there no decloupling mat fitted ?

 

[Fraser Tiling]

The underfloor should have been commisioned before tiling. I'm pretty sure this is the moisture from the screed trying to get out.

Thanks Chalker, that makes alot of sense, will check with the builder that the UFH was tested before hand, I must admit I cant remember whether I asked, to be fair with their experience they should know.
Do you think there would be any staining if the screed is the issue?

 

[Fraser Tiling]

Was there no decloupling mat fitted ?

no, wasn't deemed necessary by the builder, dont think there would be an issue if it was used

 

[Fraser Tiling]

Back home now and had a closer look. I didn't pick up on the uncommisioned ufh part.
I'd say that it's primarily the additional moisture of the extended set not yet gone, and in part - moisture rising from the screed still.
Good sign is the dryness around the grout joints. I think this will dry out but could take quite some time yet...

For future - please use Ditra and a rapidset. That would mean you could fix safely onto uncommissioned heated screed and no risk of residual moisture lurking in the adhesive.

agreed, I would never spec a floor and not use a decoupler