Heavy tiles onto skimmed moisture board

[Olly]

I'm looking for some reassurance that I can get away with tiling onto the skimmed moisture resistant plasterboard that is around my new bath.

I wasn't planning on using heavy tiles when I prepared the bath surround and didn't feel the need to fully waterproof it as there is no shower spray so just had the plasterboard skimmed and then primed it ready for tiling.
Now I have 12mm thick marble veneered ceramic tiles and an worried that I am running a risk that they may be too much for the substrate.
The tiles are 600x300 and I only intend to fix 2 rows above the bath. The weight per m2 obviously exceeds the max for skimmed plasterboard but over a relatively small area do I need to be overly concerned?

My solution if the plaster wont hold will be to cut out a 800mm wide band of the plaster board and fit hardiebacker to fix the tiles to. with the mess and faff of adding extra noggins etc. I really could do without it.

Any advice greatly received!

 

[J Sid]

you have answered you own question correctly .

 

[Waluigi]

The Tilers Forums answer would be to do it properly by taking the board off and replacing with a TBB

In reality, it’s two tiles up from the bath, it’s plaster that was skimmed directly onto board so you should know how good the bond is so in reality it would be fine.

However, we are professionals here so we wouldn’t be able to do such a thing for a paying customer.

 

[Boggs]

Does anyone else notice that skim doesn’t adhere as well to moisture resistant board as to normal board.

 

[acaciaguy]

Yes. It’s fine if it’s just skimmed. Wouldn’t fancy any weight on it

 

[Waluigi]

Hang on, it’s MR board?!

I take back my statement. MR board shouldn’t be skimmed full stop.

 

[acaciaguy]

I agree.

 

[Boggs]

Hang on, it’s MR board?!

I take back my statement. MR board shouldn’t be skimmed full stop.

There we go

 

[Boggs]

What’s happened there?

 

[Waluigi]

There are some exceptions.

Can you skim an MR grade board? - https://www.british-gypsum.com/technical-advice/faqs/082-can-you-skim-an-mr-grade-board

 

[Olly]

Thanks for the contributions.

I appreciate that I should have set out differently before boarding the room but I didn't know what tiles or layout I was going for until after the bath was in.

The Moisture board was primed with pregrit before skimming to get a good bond.
I might try a test patch by sticking on an offcut and see what fails when I lever it back off the wall once set. If it's hard work and the paper/plaster bond doesn't fail I'll get tiling.

 

[Waluigi]

You would probably be ok then. I’d be a bit worried if multi/board finish was slapped on with no primer

 

[Cranbrook]

There are some exceptions.

Can you skim an MR grade board? - https://www.british-gypsum.com/technical-advice/faqs/082-can-you-skim-an-mr-grade-board

Ive argued with a number of different plasterers until I was blue in the face about this topic, none of them will ever listen!

 

[widler]

You can skim without doubt skim onto moisture board, but it needs blue grit 1st, moisture board has a coating on it which just skim won’t adhere too .
As for holding the weight , probably, try one, stick it on, leave a day or two and try and rive it off

 

[Boggs]

A few newer build properties I have worked on lately have had skimmed moisture restistant board in bathrooms and had been tiled over.

Taking the tiles off left the fully intact board almost as good as new.

Paint scraper behind skim that was left took it straight off.