Keraquick + 600x600 Porcelain + Andhydrite Screed - UFH DISASTER!

[kevin.pritchard]

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

 

[Ian]

Good morning Kevin. A couple of questions about the prep, was the laitence sanded off the screed before tiling? And was the UFH commissioned? Also, was a moisture test performed? With regards to the adhesive, anhyfix from tilemaster is a gypsum based adhesive and is specifically designed to work with these screeds. You may have a stockist closer to you but, I use tiletown in Derby for my tilemaster products, they deliver nationwide and have a service that is second to none. Here is a link to the product on their website Tilemaster Anhyfix, Gypsum Based, Flexible, Rapid Setting Floor and Wall Tile Adhesive

 

[Andy Allen]

just to add was the floor primed, and how soon was the heating turned on after tiling, and was the heating turned on low to begin with and turned up slowly over a period of time..

 

[kevin.pritchard]

was the laitence sanded off the screed before tiling?

No, not sanded, but the screed has been down for 2 years and has had a lot of traffic and has been scraped with a floor scraper about 20 times over. Floor was scraped and hoovered prior to laying.

was a moisture test performed?

No. I presumed that after 2 years of heating would dry the slab well and truly!

anhyfix from tilemaster is a gypsum based adhesive and is specifically designed to work with these screeds

Will this cope well with the daily expansion and contraction of a heated slab? Thank you for the link

just to add was the floor primed, and how soon was the heating turned on after tiling, and was the heating turned on low to begin with and turned up slowly over a period of time..

Floor wasn't primed. Heating was turned on 2 months after tiling. It was on for about 3 hours one evening at a flow temp of around 46ºC. The following evening, heating wasn't turned on. A few tiles at this point began to show signs of loss of bonding.

 

[kevin.pritchard]

Hopefully this photo will help matters.

 

[kevin.pritchard]

I think I can see the problem. The adhesive hasn't gone into the waffle

 

[Ian]

From the photo it looks like there is no bond between the adhesive and the screed and also very little bond between the tile and the adhesive. I'd say you've used an 8mm trowel and not backskimmed the tiles which hasn't given you a solid bed. Anhyfix is the best product to use IMO and yes, it is suitable for heated screeds. Have a read through the PDF on my previous link.

 

[kevin.pritchard]

From the photo it looks like there is no bond between the adhesive and the screed and also very little bond between the tile and the adhesive. I'd say you've used an 8mm trowel and not backskimmed the tiles which hasn't given you a solid bed. Anhyfix is the best product to use IMO and yes, it is suitable for heated screeds. Have a read through the PDF on my previous link.

8mm yep - too little?

Not backskimmed - you're right. I've probably ballsed the whole thing

So the Keraquick is not to blame?

If i strip the whole area, prime, 10mm trowel, back skim tiles, you think i'll be solid for good?

Thank Bri. Much appreciated.

 

[Ian]

I always start with a 10mm and backskim the tiles, if the floor is a bit up and down a 12mm may be necessary. You really need to remove the lot and start from scratch. Get the floor sanded and hoovered, prime, then tile with anhyfix. Don't forget to backskim the tiles to fill in the waffles and lift every other tile to ensure the ribs in the adhesive have collapsed and you have a solid bed.

 

[kevin.pritchard]

Cheers mate. I'll do that and will also mix Mapei Latex Plus with the adhesive as a precaution.