Have recently had Indian limestone calibrated slabs laid in a kitchen/dining room. A dry cement mix was used to grout (point?) the gaps and it is continually shedding sand etc. Every time you sweep the floor you get a pile of dust. In some places the grount has completey crumbled exposing the screed and adhesive below.

I have had the installer back to redo parts of the floor, but this doesn't seem to have fixed the problem and I am considering having him rip out all the grout and replace it, but with what? There is wet underfloor heating under the slabs, but I don't really think this is the cause.

Anyone got any ideas about possible reasons for this problem and/or what grout should be used. The installer says he has done nothing different on this job and does not normally get this problem.

Need a flexible grout with UFH. What adhesive did he use out of interest

Hi Faithhealer,

Afraid I don't know the adhesive. Before we chose the calibrated limestone, the installer suggested some uncalibrated sandstone slabs, in which case he was planning to use a cement bed. This definitely did not happen and a proprietry adhesive was used.

A few slabs have come loose and have had to be re-stuck. A few have that hollow sound when you tap them that always makes me a bit nervous with tiles, because it usually seems to mean that they aren't stuck too well. But otherwise they seem ok.

Not sure that the UFH is the root cause, since the grout is not cracking it is just wearing away too easily from the top surface. I think the problem is called laitence when it occurs in concrete and screed floors.

bjw

Originally Posted by bjw10

Hi Faithhealer,

Afraid I don't know the adhesive. Before we chose the calibrated limestone, the installer suggested some uncalibrated sandstone slabs, in which case he was planning to use a cement bed. This definitely did not happen and a proprietry adhesive was used.

A few slabs have come loose and have had to be re-stuck. A few have that hollow sound when you tap them that always makes me a bit nervous with tiles, because it usually seems to mean that they aren't stuck too well. But otherwise they seem ok.

Not sure that the UFH is the root cause, since the grout is not cracking it is just wearing away too easily from the top surface. I think the problem is called laitence when it occurs in concrete and screed floors.

bjw

Hi, I would definatley call your installer back and lift the hollow sounding slabs. Look at the back of the slab for signs of adhesion or "not".
How old was the screed , and what adhesive was used is important! Did he skim the back of the slabs?
2Balls

Hi 2Balls,

The installer is coming back the week after next, so I'll tackle him about the hollow sounding slabs and I'll also try and find out about the adhesive.

The screed was relatively new, since it was all part of a new build extension. The back of the tiles were pre-grooved and were definitely not skimmed. The adhesive was laid and notched with a trowel before the slabs were laid.

My main concern is the crumbling pointing rather than the few hollow sounding slabs (I may live to regret that last statement), but it's driving the wife mad keep sweeping up the sandy residue!

bjw

Originally Posted by bjw10

Hi 2Balls,

The installer is coming back the week after next, so I'll tackle him about the hollow sounding slabs and I'll also try and find out about the adhesive.

The screed was relatively new, since it was all part of a new build extension. The back of the tiles were pre-grooved and were definitely not skimmed. The adhesive was laid and notched with a trowel before the slabs were laid.

My main concern is the crumbling pointing rather than the few hollow sounding slabs (I may live to regret that last statement), but it's driving the wife mad keep sweeping up the sandy residue!

bjw

Hi, Your main concern with the wife sweeping the floors will have to wait till your Tiler comes back. However, its worth checking the expansion Joints, at walls ,doors, skirting, and how big are the grout joints. It would still be good to know exactly how old the screed was!and the Adhesive!Also did the UFH go through UP- Stay- Down for a few days?

2Balls

Hi 2Balls,

What am I checking for in the expansion joints etc? Generous gaps were left all round and skirting was fixed on top of the floor. The grout joints are quite wide, generally about half an inch and sometimes bigger due to the natural variation in the slabs.

I doubt anyone will be able to say exactly how old the screed is now. Because the sub-floor etc was all new, I would guess the concrete base was a couple of months old and the screed to surrounding the UFH pipes had at least a couple of weeks to dry out.

Finally, don't quite understand the following could you clarify for me please: "Also did the UFH go through UP- Stay- Down for a few days? "

bjw

Hi, Its worth checking the expansion joints ,there should be no adhesive or grout!. When the Screed is a normal sand cement mix over insulation and membraine,a minimum 28 days Drying Time. Your UFH should then go" UP" 3 days , Then "Stay "3 Days, then cool "Down" 3 days. Then check, if everythink OK is, Then lay your Slabs.It might not just be a grout problem!
2Balls

A sand cement mix with no modifier is probably why it is coming out of the joints.....Should really have been a polymer modified wide joint grout used to cope with expansion and contraction of the floor...

The hollow sounding is more than likely debonding of the tiles or insufficent adhesive ( voids)....

This needs sorting along with the grout as it will just be a matter of time before you get a knock on effect.....but the sand/cement grout mix deffo needs to come out and be replaced with corrrect product...

If you fixer isn't prepared to do this then employ someone who is....


good luck..

p.s....also how thick was the screed over the wet heating........2 weeks you say to dry out..?

Hi,

I'm pretty sure the UFH didn't go through anything like the procedure you describe. What sort of problems might this give rise to?

Expansion joints around the edge are now covered by skirting, so no longer visible. There are no other expansion joints in the floor space itself.

I think that plenty of drying time for sub-floor, screed etc was allowed (the whole job took long enough!), just can't say definitively how much was allowed at each stage.

Given that large parts of the grout appears quite solid but just has a tendency to shed grains when rubbed or brushed, how might the sort of problems you describe make this happen?

bjw

Hi ,Sreed cracking,or crumbling,making the slabs loose and grout cracking.2Balls

Why would he use a dry cement mix, If it's that weak needs to be redone

Watering can! HE HE2Ballls

He has swept in a dry mix sand concrete mix and the used watering can to wet it down, this never works.
Here is a link to paving expert and pointing slabs, this is an excellent site for paving.
http://www.pavingexpert.com/pointing.htm#point


Hope this is allowed.

You can get a polymetric jointing compound that you can brush in that sets hard but I don’t think you will beat wet pointing with slabs.