Porcelain SLC over old tile adhesive

[Steve_Bcs]

Further to my other post re our hollow tiles issue It looks like our tiler has dot and dabbed most of our floor to accommodate tiling 800x800 porcelain over an uneven floor.
The gap from defrac membrane to the underside of the tiles in question is around 20mm. The membrane sits directly on our retrofit ufh system.

Whats the best way of filling the voids before replacing the tiles?. Can we lift the tile ( approx 20 nr) leave the dabs in place ( or trim down 10mm or so & fill with deep fill slc? Is there a derp fill slc that doesnt need a primer? I am concerned that chiselling out the adhesive may risk damaging the ufh pipes. Thanks.

 

[Steve_Bcs]

Just lifted two tiles by gently prising the (protected) edges along 2 sides. Adhesive is almost 50mm.

 

[Dexter]

Should have been latex before tiling, you obviously got high differences between rooms, No proper tiler would have dot and dab the floor though as you needs to be full coverage of adhesive, if the tiles come up as easily as they look in the picture I would take up all the tiles & latex the floor and re-tile using am S1 adhesive

 

[Slippery]

I think this is best answered by the SLC company, I think it could work filling in the gaps and you will at least have a datum to work to but then I think to be safe, you would need to overlay the floor with a cement fiberboard so you are only fitting to one type of substrate.

 

[Steve_Bcs]

Thanks. Since posting, the adhesive manufacturer (Ultratile) have said we should remove as much adhesive as we can and then pour their prolevel ultimate product, which doesn't need the substrate priming. Then prime & tile as normal with 100% coverage.

They also said the whole floor needs to be lifted as its likely the lot has been dot and dabbed ( 50sqm). I started lifting yesterday and they were right!

Unfortunately we cant come up any more or overlay boards due to having low profile exterior sliding door thresholds so as chiseling isn't an option I’ve now bought a 2 handled concrete grinder with dust extraction and will carefully grind down each dab by 10mm across the whole floor. I’ll make a wooden tile-sized template and use my laser level to ensure a consistent level. Its going to be a tad laborious but not a job I want to trust to the tiler to fix.

He has now agreed to relay the whole floor & pour the slc at his expense. He admitted it was wrong of him to dot & dab over ufh. We will only need about 10 new tiles to cover lifting breakages, which are in stock ( same batch) so hopefully the saga will soon be over.

 

[Slippery]

Thanks. Since posting, the adhesive manufacturer (Ultratile) have said we should remove as much adhesive as we can and then pour their prolevel ultimate product, which doesn't need the substrate priming. Then prime & tile as normal with 100% coverage.

They also said the whole floor needs to be lifted as its likely the lot has been dot and dabbed ( 50sqm). I started lifting yesterday and they were right!

Unfortunately we cant come up any more or overlay boards due to having low profile exterior sliding door thresholds so as chiseling isn't an option I’ve now bought a 2 handled concrete grinder with dust extraction and will carefully grind down each dab by 10mm across the whole floor. I’ll make a wooden tile-sized template and use my laser level to ensure a consistent level. Its going to be a tad laborious but not a job I want to trust to the tiler to fix.

He has now agreed to relay the whole floor & pour the slc at his expense. He admitted it was wrong of him to dot & dab over ufh. We will only need about 10 new tiles to cover lifting breakages, which are in stock ( same batch) so hopefully the saga will soon be over.

I'm glad you have reached an agreement, make sure he back butters the tile also as the ones laid were not stuck to the adhesive.
If there is any dust film, wipe with a damp cloth, then spread the back, IMHO, the most important thing when laying large tiles!

 

[Steve_Bcs]

Update
Further to this & my other posts about my newly laid dot & dabbed 800x800 porcelain kitchen floor (50sqm) over ufh…

So, The plan was to grind down the dabs by 10mm then pour slc into the voids and then a 5-6mm coating over the top.

That didnt go well, my dust shroud with hoover attached on the concrete grinder worked on flat area but when trying to grind over dab & voids the dust blew out everywhere. It was taking forever, getting a consistent level across dabs was proving difficult. I abandoned the idea as it just wasnt practical or effective.

Called a commercial floor grinding firm - but at circa £2.5k not really an option.

Plan B
Remove all the adhesive. The dabs of adhesive were laid on a Kerakoll bio tex crack mat (Our tilers choice). These actually prised off the mat pretty much in whole pieces with gentle persuasion from a thin blade bolster chisel gently tapped underneath to break the seal then just pulled up. .

After a few days they were all up & in the skip. Tiler back tomorrow. He wont be expecting the whole lot gone.

The crack mat is now a fluffy mess so I’m scraping as much off as possible. This should be the tilers responsibility but I’ve done all the removal work so far while he has been away. He’s got off quite lightly so far!

Utratile’s tech dept advised that every last fibre of the crack mat has to be scraped or ground off & the floor primed with 2 coats of MSP Multi Surface Primer, before slc can be laid. (Prolevel ultimate) which I’ve already had delivered

I tried grinding with an angle grinder & a carbide ribbed cub blade but managed to graze an ufh pipe which are just 3 mm below the surface ( retrofit system). So grinding is too risky. Tried wetting it & scrubbing which worked but will take days.

So looking for advice really as to how to mechanically remove the remaining fibres that will not damage the underlying adhesive bed. Floor sander? Or floor polishing machine with a scrubbing pad maybe?

I’ve got a firm booked in to properly level the floor on Aug 21st so the tiler has some time to get the mat up.

Any thoughts or advice welcome.