18mm cement board UHF

[shongu]

I think that is exactly what's happened.
The floor was primed but they used a 6mm plastic trowel to put it down and did not fill properly underneath. When they realized it didn't stick they started screwing the loose areas

 

[Time's Ran Out]

 

[Time's Ran Out]

Not the ideal video but it’s an apt and great song IMHO.

 

[Dumbo]

I think that is exactly what's happened.
The floor was primed but they used a 6mm plastic trowel to put it down and did not fill properly underneath. When they realized it didn't stick they started screwing the loose areas

It is designed as a floating system , and you now how we all love those .

 

[Bill]

To be fair, the last one I did with these boards, the boars were only screwed down onto 22mm ply but there have been no issues at all.

The manufacturer stated that they could be tiled straight onto with a flexible adhesive and that's what I did. I used a Norcross one too, so I think that so long as you prime them sufficiently, a quality flexi addy and you will be fine.

The correct commisioning of the heating is ultra important to the success of the tiles keeping their bond.

This is the stuff I used, over 2 years now

https://www.tileexperience.co.uk/co...s-rapid-porcelain-tile-adhesive-grey-20kg.png

But with stone, you will need to use crack mat.

 

[Flintstone]

Can somebody answer me if the boards are gypsum or not?

 

[wayne]

I tiled one over a year ago with flexi addy straight onto the boards after priming. Been back recently and the job is still spot on.

 

[Dumbo]

Can somebody answer me if the boards are gypsum or not?

I was told they are gypsum . But something called spent gypsum so wouldn't react . I may of misunderstood what I was told though .

 

[shongu]

I've looked into it and its material called dry screed. The main component is calcium sulfate which is gypsum. So priming is key. Water absobsion is 30% without priming.

 

[Old Mod]

Yes these systems are loose lay, they’re supposed to level floor first and then glue board edges together as they’re laid, creating one large sheet.
Done correctly, they don’t move, the weight is colossal.
Prime the entire area thoroughly, applying at least two coats perpendicular to each other, use a grit based primer on plastic areas. (Prime & grip or similar)
Charge the system to 5-6 bar cold and latex with 5mm covering above pipes.
This causes pipe expansion, so when the system is discharged they contract leaving enough room for the pies to expand and contract when in use.
Minimising the risk of movement.
Anti fracture mat, it’s stone, it needs one.
A 1mm mat would be sufficient, no need for Ditra, although it will offer a higher level of protection.
Tile
and correct ufh commission, is paramount.