Painting Marmox or Wedi board

Hello,

I am new here, need some help please.
I am tanking a small bathroom with Marmox multiboard or Wedi board (probably Marmox it is cheaper).
However there is a sloped ceiling which will partially be in the shower cubicle and get wet, it intrudes into the room quite far down to 150cm from the floor.

I do not want to tile this sloped ceiling, currently it is ordinary plasterboard with waterproof paint. I would like to keep a similar finish but replace plaster board with Marmox board.

To cut a long story short, how can Marmox board be finished so it can be painted? I would rather not plaster it, unless there is some modern plaster that is not going to be affected by water.
Is there a way to just render and paint the Marmox board directly?

Thanks

In a nutshell - just tile it or leave it as it is plaster with waterproof paint.

Answer from Marmox: there are modern concrete finishes very popular abroad for wetrooms, these are suitable for Marmox board.
Wedi has one smooth surface but I did not ask them about what paint is best.

"I can understand why you don't want to tile that sloping ceiling but the Marmox board without any coating is generally not suitable as a finished surface, even if painted. Marmox boards have been installed and just painted (with masonry paint) before but only in areas where the appearance is unimportant such as in store rooms or workshops. Our board has a very deep texture so would look pretty unpleasant if just painted.....especially with waterproof sealant or tape between the joints.
When not being tiled, our board is usually plastered with a light skim coating but plaster and showers are most definitely not compatible.
One suggestion I would have is waterproof concrete. You would need to waterproof the board edges - not with waterproof tape but with our sealant, Marmox Multibond. Unlike Silicon, Multibond does not shrink, crack and importantly, not stop things sticking to it, such as tile adhesive, plaster, paint or concrete. I mention concrete because instead of a plaster coating you could apply a concrete coating. In the UK, external waterproof concrete coatings or "renders" are popular but internal waterproof concrete coatings are not as common. In Asia, it is common to find wet rooms not tiled but finished with a smooth, polished waterproof concrete finish. Such materials: waterproof concrete, are available but you need to look a little harder to find one. We do not have any experience of these so I can't help you identify a suitable one. However, I can say that our Marmox board which has a concrete skin is an ideal base for a waterproof concrete finish."

My other option is something like Altro Whiterock uPVC sheeting, but am not keen on having to glue this to Marmox boards.

I'm struggling to understand why you want to use a tanking board and then paint It?

Use a one piece thin porcelain or a shower board such as Bushboard.

The tanking board is of course because the area we are talking about is inside a shower cubicle. To protect bricks, floors from water and moisture.
The paint is because I don't want to place 60x30cm tiles on a reverse slope up to the ceiling 2.4m high. Any mistake with adhesive and the thing could come crashing down.
Since I don't want to tile that high, I still want a nice traditional finish, usually sloped ceilings which intrude into a room in 1920's and 1930's style properties are plastered and painted matt white. I want to try to retain a similar finish.

But you still want paint on a surface within a splash zone yes?

Gor said:

The paint is because I don't want to place 60x30cm tiles on a reverse slope up to the ceiling 2.4m high. Any mistake with adhesive and the thing could come crashing down.
Since I don't want to tile that high, I still want a nice traditional finish, usually sloped ceilings which intrude into a room in 1920's and 1930's style properties are plastered and painted matt white. I want to try to retain a similar finish.

Click to expand...

If fixed correctly using the correct materials and methods they will never come down. If you want a traditional finish, then ditch the shower and just have a bath with a wet room configuration. Nothing traditional about a shower cubicle whereas a wet room can retain a period look without being too intrusive.

Yes I want a painted surface within the splash zone, if I chose the finishing waterproof concrete or what ever its caller.
If I go for the uPVC sheeting they offer a satin version so no paint needed there. I am leaning towards uPVC sheeting as its more readily available and should easier to install than this waterproof concrete stuff.

Point taken showers are not a very period feature.
I want a white finish for the ceiling and sloped ceiling meeting the vertical tiled walls. If you have a better solution to achieve this combination than above I'm all ears.

Its effectively like this here, except its not a walk in its an enclosure. But position is identical, in the corner where the slope is.

A bit more web digging and speaking to technical departments.
So for anyone wishing to use cement insulation board for ceilings (such as Marmox or Wedi) instead of plasterboard.
Options are, microcement.
And another weird option, monocouche renders (external). Some have a fine finish, and some work well with insulation boards and cement boards. They can also be painted in masonry paint.
Sounds a bit nuts maybe, but should be a more durable finish than plasterboard or plaster painted in bathroom paint.