Keraquick + Adhydrite Screed = UFH Nightmare!

Hello Tile Gurus 

I have already laid about 35m2 of 600x600 porcelain tiles onto a very dry (2 years drying time) anhydrite screed. I used Mapei Keraquick with a notched trowel and allowed 2 months before turning on wet UFH. The were solid as a rock.

Within days of having the heating on, several tiles began to sound hollow and eventually rattle.

To cut a long story short, I'm having to rip the lot up, clean the tiles and scrape the floor. NIGHTMARE!

What alternative approach should I take to this in terms of adhesive, prep etc.?

I am thinking, as belt an braces, to just go for BAL Single Part Fastflex (seems to be very elasticated?), but it's going to cost around £350-£400! The Keraquick was only about £90.

Any thoughts welcome.

Cheers,
Kev

Yep, 2 things in play here, the first is the movement, anhydryite is gypsum based so it expands a lot and quickly, secondly cement based adhesives react with gypsum based ones and you need a seperation.

Turn the heating off, remove the loose chalky stuff (may already have gone) and make sure the slab is cold, prime with 2 coats of neat acrylic bonding, then use an S2 spec flexible adhesive - we use granfix ultimate flex, or granfix rapid set flexible with the flexi polymer additive.

Leave the heating off for 48 hours, then slowly crank it back up to normal over the course of a few days.

Other manufacturers are around, obviously but both granfix and bal with give you a written specification and as long as this is followed they will guarantee it.

tpt said:

Yep, 2 things in play here, the first is the movement, anhydryite is gypsum based so it expands a lot and quickly, secondly cement based adhesives react with gypsum based ones and you need a seperation.

Turn the heating off, remove the loose chalky stuff (may already have gone) and make sure the slab is cold, prime with 2 coats of neat acrylic bonding, then use an S2 spec flexible adhesive - we use granfix ultimate flex, or granfix rapid set flexible with the flexi polymer additive.

Leave the heating off for 48 hours, then slowly crank it back up to normal over the course of a few days.

Other manufacturers are around, obviously but both granfix and bal with give you a written specification and as long as this is followed they will guarantee it.

Click to expand...

Thanks tpt. So you reckon the problem all along was that the Keraquick was reacting with the screed and needed a prime of acrylic bonding?

Hopefully this photo will help matters.

as tpt
needed a two coat primer..across the floor then up the floor 100% coverage this way... and then a ditra or dura+ matting imo

and then follow mfr inst regarding warm up time..what grout spacing did you use...looking at pics...looks min..

Plan of action now is:

1. Remove tiles and adhesive
2. Sand floor
3. Prime with Timemaster Prime Plus
4. Use 10mm trowel with Anhyfix, 1mm back butter
5. Follow Timemaster warmup guidelines
6. Eat Christmas Dinner