hedgecutter

iTrader: (5)

Any tilers/ builders on here? I'm interested in hearing your preparation methods/tips for tiling on Anhydritic flow screeds with ufh. 15mm limestone tiles.
thanks

BMWhere?

I'm not a pro, but tiled a room in my cellar over Christmas with a screed floor and under-floor heating. For my first shot at tiling I was very pleased with my results!

First sweep the floor, remove any dust and debris. Flow screed should normally be dead flat, but you may find some protrusions at the edges which you may want to remove. Any small unevenness isn't a problem as the tile cement will even everything out.

Pre-treated the screed with a primer -> https://www.pci-augsburg.eu/en/produ...oxigrund-rapid

Then used a flexible tile cement -> https://www.pci-augsburg.eu/en/produ...flexmoertel-s1

Not sure how easy the above products will be to get in the UK, but there will at least be an equivalent.
The flexible tile cement is really important if you have under-floor heating!

I recommend using a tile levelling+spacing system to get the tiles nice an even.

Lay everything out dry and pre cut tiles before mixing your cement as you only have a limited working time before the cement hardens. Working alone, I was mixing half a bag of the cement I linked above and was just about right for the area I could cover in the time it hardens. If you have a helper to lay the tiles while you lay the cement, then you could manage a full bag in one go! I needed 2 bags for a room 3m x 4m but will depend on how thick you need to lay the cement for your tile size.

hedgecutter

iTrader: (5)

Thanks for taking the time to reply, good advice. Was your screed a traditional Portland cement mix, or was it a flow screed?.....as flow screeds aren't strictly cement , but calcium sulphate binder with sand mix, that reacts with water to form gypsum . As such it has a couple of issues that have to be dealt with before tiling
The 1st is a weak layer of laitance that forms on the surface, which needs to be removed prior to tiling.
The 2nd is ettringite, a mineral that forms at the interface between the gypsum and tile adhesive, which again could cause de bonding.
As I've got nearly 100m2 of tiles to lay, I need to get the procedure right, and as usual there are differing products, methods and solutions offered on the interweb. So I'm hoping for some clarity on removing laitance , andhydite primers/ cements, and decoupling mats.
There are always more complications in self builds than expected, as I thought I could just prime and stick, but unfortunately that's not the case. Calcium sulphate screeds also need to be really dry.

BMWhere?

Yes, it was a flow screed, but the mix in Germany could be different from UK.
You could sand the surface before priming, I read that was useful, but didn't bother in my case as there wasn't really a residue on the surface. I ended the concrete walls though as there was a residue on that.
The primer is the important part to avoiding debonding. It's important to get a primer that is specifically designed for rolling screed. The primer should also be breathable to ensure moisture can pass through it.