Moisture Resistant Plasterboard

[MortarThePoint]

I've chosen MR plasterboard for the kitchen ceiling, bathrooms and window reveals. We're also skim finishing everywhere with Multifinish. Based on the text below it looks like it's pointless using MR boards since the skim isn't moisture resistant. Am I overlooking something or has everyone else who's chosen MR boards taped and jointed? Is the jointing compound moisture resistant?

 

Plastering

Skim plastering should not normally be specified to

Gyproc Moisture Resistant and MR grade boards. These

types of board are intended for use in environments of

higher than normal humidity for which no gypsum plaster

is designed to be suitable. Where moisture resistant

board options are used in shell and core construction to

provide temporary resistance to high moisture conditions,

they can be skimmed at a later date after the building

envelope has been made weather-tight. Plaster should be

applied only to the face of moisture resistant boards and

pre-treatment with ThistleBond-it is required.

https://www.gyproc.ie/sites/default/files/Gyproc Moisture Resistant PDS_Final.pdf

 

Edited November 14, 2023 by MortarThePoint

[Eric]

I think you use a special primer/sealer on moisture resistant, I’m sure someone like Nod will keep you right. 

[MortarThePoint]

If the skim gets moisture damaged, can the base plasterboard still be OK and can you strip back to it to recoat?

 

2 minutes ago, Eric said:

I think you use a special primer/sealer on moisture resistant, I’m sure someone like Nod will keep you right. 

 

BG recommend Thier ThistleBond-It primer.

 

Yes @nod will have some good points to raise.

[MikeGrahamT21]

I’ve never thought of it this way, but I wonder if MR boards aren’t anything to do with using in a bathroom and more to do with being able to install them in a wet building to save time. The fact they need bonding before plaster would agree with that.

 

im thinking along the lines of like chipboard flooring with the peel back coating, another product so you can crack on and ignore other factors.

 

I’m more than likely wrong, but just made me wonder when I read the BG blurb

[nod]

52 minutes ago, MortarThePoint said:

If the skim gets moisture damaged, can the base plasterboard still be OK and can you strip back to it to recoat?

 

 

BG recommend Thier ThistleBond-It primer.

 

Yes @nod will have some good points to raise.

We thistle bonded moister boards for about five years Totally unnecessary 

Then nothing for about ten years 

I’m currently doing a site where they have insisted on this Total waste of money 

[MortarThePoint]

1 hour ago, nod said:

We thistle bonded moister boards for about five years Totally unnecessary 

Then nothing for about ten years 

I’m currently doing a site where they have insisted on this Total waste of money 

 

I have the boards now so am wondering if I should not use them. Is there any moisture resistant skim made by others?

[MikeGrahamT21]

Gypsum in any form is water soluble, I really think this is more about moving builds on quicker than anything to do with them being suited for bathrooms. By the time the moisture has reached the board you’d be in trouble anyway.

 

just come across this, lime plaster on fibre reinforced cement board, for exterior use:https://biolime.com/bl_system/cement-board-exterior/?bl_system_choice=7062&square_feet=

 

Where abouts is the wall located in terms of moisture? Near a water source? You thinking skim and paint?

 

hmm intriguing…apparently you can skim, seal with SBR bond, sand it slightly for a key and then paint on top of that? I have zero idea if that works but if the paint adheres as people say it will, the layers are in the right place to do the job.

Edited November 14, 2023 by MikeGrahamT21

[nod]

1 hour ago, MortarThePoint said:

 

I have the boards now so am wondering if I should not use them. Is there any moisture resistant skim made by others?

If they are being tiled I would just tape the joints If not you can skim over them like any other wallboard 

[MortarThePoint]

As the extract in first post, BG recommend joint & tape for MR boards, but their joint filler is Gypsum based and has the same moisture text in its datasheet as in the MultiFinish datasheet:

 

Effect of moisture and condensation
Don't expose the plaster to moisture repeatedly or 
for long periods of time, as this can cause it to lose 
strength and adhesion.

MultiFinish

 

Effect of moisture and condensation

Don't expose the product to moisture repeatedly or

for long periods of time, as this can cause it to lose

strength and adhesion.

Joint Filler

 

That means there is no complete system that makes MR boards work.

 

Am I missing something here! Do others make MR joint filler?

 

11 hours ago, nod said:

Total waste of money

Agreed!

[Russell griffiths]

Why use MR plasterboard in the first place, you won’t have high levels of humidity. 

Your MVHR  will have taken that away before it gets anywhere near the ceiling, unless it’s a 2x2m room with a 5 ring hob boiling water constantly then your over thinking it, these boards where designed for older style houses to overcome a problem, you won’t have that problem. 

 

You dont need it on window reveals, they should be insulated enough to not be getting any condensation or damp, so sort that issue instead of fitting a board that doesn’t mind being damp. 

 

Dont fit a bandaid to cover a problem, design out the problem. 

 

Normal board or pink for fire rating or blue for sound, but MR not needed. 

In a bathroom you should be tanking wet areas, so it’s not needed there either, and there are better boards than MR for that also. 

[nod]

1 hour ago, Russell griffiths said:

Why use MR plasterboard in the first place, you won’t have high levels of humidity. 

Your MVHR  will have taken that away before it gets anywhere near the ceiling, unless it’s a 2x2m room with a 5 ring hob boiling water constantly then your over thinking it, these boards where designed for older style houses to overcome a problem, you won’t have that problem. 

 

You dont need it on window reveals, they should be insulated enough to not be getting any condensation or damp, so sort that issue instead of fitting a board that doesn’t mind being damp. 

 

Dont fit a bandaid to cover a problem, design out the problem. 

 

Normal board or pink for fire rating or blue for sound, but MR not needed. 

In a bathroom you should be tanking wet areas, so it’s not needed there either, and there are better boards than MR for that also. 

To be fair 

If water gets past the tiles and waterproof tile adhesive ,you’re pretty much stuffed