Moisture resistant Plasterboard - plastering

[kevd]

I am thinking of using moisture resistant plasterboarding to board our my ensuite - as its a fairly humid area.

The shower area will be tanked and then tiled, but for the rest I was going to have it plastered and then paint it.

However, reading the details on the Gyproc site regarding the moisture resistant board, it says that ...

"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 Thistle Bond-it is required."

My question is, is it ok to do a finish skim coat of plaster onto moisture resistant board - I guess it has to be bonded before hand? Or, should I just use normal plasterboard?

I am going to try to get a quote from a local plasterer soon, but wanted to check then general consensus here also.

 

[Comic-Gnostic]

Well done for reading the instructions. I would get your quote and when you do... ask him to write down what materials he will use. He will either using a bonding agent (which is a better all around finish, or he will just use some PVA mix which works but i don't think its better)

1./ water resistant board
2./ pre treatment bond-it or PVA(on the raw plasterboard)
3./ multi finish but preferably bonding coat(skim)

Don't use normal plasterboard, use the instructions for bathroom plasterboard.

You are on the right direction, stay on this direction.

Normal plasterboard will rot and will probably be the cause of future mold infestation.

ahh this is my first post i hope it helps.

 

[nick13]

Well done for reading the instructions. I would get your quote and when you do... ask him to write down what materials he will use. He will either using a bonding agent (which is a better all around finish, or he will just use some PVA mix which works but i don't think its better)

1./ water resistant board
2./ pre treatment bond-it or PVA(on the raw plasterboard)
3./ multi finish but preferably bonding coat(skim)

Don't use normal plasterboard, use the instructions for bathroom plasterboard.

You are on the right direction, stay on this direction.

Normal plasterboard will rot and will probably be the cause of future mold infestation.

ahh this is my first post i hope it helps.

Never put PVA on any type of plasterboard. Moisture board and standard skim will do just fine. If the relative moisture content 1s prevalently above 80% you can seal the finished surface with SBR.

Nick

 

[Comic-Gnostic]

Never put PVA on any type of plasterboard. Moisture board and standard skim will do just fine. If the relative moisture content 1s prevalently above 80% you can seal the finished surface with SBR.

Nick
pebble-dash.co.uk

Yes thanks for clearing that up . Yes i agree do not use PVA on raw plasterboard.

 

[kevd]

I think I might know the answer to this - if its the same as gets said in the tiling forums, but could you remind me why you can't PVA onto bare boards?

When the plasterers did my kitchen, thats exactly what they did - watered down PVA!

 

[Richard C]

I think I might know the answer to this - if its the same as gets said in the tiling forums, but could you remind me why you can't PVA onto bare boards?

When the plasterers did my kitchen, thats exactly what they did - watered down PVA!

PVA is not normally necessary on wall board but you can & under certain circumstances should use it; it won’t do any harm & if you’re a novice, will even give you a bit more time.

EDIT
Sorry just realised we may be referring to MR PB ; it should be left to dry out thoroughly before skimming & you need to prime it prior to skimming; use either "Thistle Bond It" or PVA with a little cement thrown in. Standard wall board will be OK.

 

[kevd]

By dry out - do you mean existing wall if damp or dry out after bonding before skimming?

I shall ask plasterer I speak to about using Thistle Bond it - thats also what Gyproc say.

Don't suppose there are any decent (be honest ) plasterers on here near Basingstoke?

 

[Cumberfinger]

Hi.
everyone seems to be pointing you in the right direction!
Just wanted to give you a little more confirmation!
Moisture resistant plasterboard (or Moisture-check) has a percentage of silicone mixed into the gypsum core, along with a small percentage of glass-fibres for reinforcement (though this percentage is far smaller than other products, such as Fire-check. (pink)).
This does NOT make the board waterproof!!
It does, however (as it says) give greater resistance to moisture than ordinary (white/grey) board.

Further, most manufacturers seem to recommend (some insist) using their own patent, branded bonding product.
I have only ever found a very small handful of specialist applications where this is necessary, & otherwise have never had any problems related to skimming (or taping) direct to moisture-board.
I think it's probably a case of the manufacturers doing a bit of CYA.
My own personal preference is for the Lafarge product, but this is purely from an installation point of view as I find their board crisper & easier to work with.
Post installation, the point is entirely academic & makes absolutely no difference to the finish.
All the best, & please feel free to ask more!!

 

[Richard C]

By dry out - do you mean existing wall if damp or dry out after bonding before skimming?

I shall ask plasterer I speak to about using Thistle Bond it - thats also what Gyproc say.

I think it may only be relevant on new builds where the ambient humidity of the building fabric is very high but I’m not really sure why there is a “warning on the British Gypsum tin” as it were; possibly due to the construction of the MR plaster within the board. I’ve never had any problems skimming it on refurbishments (never skimmed a damp new build using MR) but if there has been a lot of moisture involved, I just give it some time to dry out & settle down prior to tiling or skimming. I don’t normally use Bonding as a base over any boards (sometimes over Artex), I just skim out as normal; but if I did, I would apply normal practice, finish skim as soon as it’s gone off or it’ll suck the time (& life) out of you.

Don't suppose there are any decent (be honest ) plasterers on here near Basingstoke?

Can't help with that one.

 

[Richard C]

Moisture resistant plasterboard (or Moisture-check) has a percentage of silicone mixed into the gypsum core, along with a small percentage of glass-fibres for reinforcement (though this percentage is far smaller than other products, such as Fire-check. (pink)).

That may explain some of it.

This does NOT make the board waterproof!!

Indeed & is something I constantly tell folks refurbishing bathrooms!

It does, however (as it says) give greater resistance to moisture than ordinary (white/grey) board.

But not much.

Further, most manufacturers seem to recommend (some insist) using their own patent, branded bonding product.
I have only ever found a very small handful of specialist applications where this is necessary, & otherwise have never had any problems related to skimming (or taping) direct to moisture-board.
I think it's probably a case of the manufacturers doing a bit of CYA.

You rarely if ever need to use overpriced support products.

My own personal preference is for the Lafarge product, but this is purely from an installation point of view as I find their board crisper & easier to work with.
Post installation, the point is entirely academic & makes absolutely no difference to the finish.

What’s generally available seems to be regional but I’m sure it makes no difference; whatever floats your boat.

 

[kevd]

Cool, cheers all for all your help.

I fully understand that MR board is NOT water resistant or proof in any way.

Its more of a belt and braces do it properly approach - as I have the choice now before starting and its not much extra. I only really thought about it cos the room can get really humid after a shower (even with a fan going) so thought that any attempt (however vain!) may help slightly.

I am glad that it seems not to matter much about skimming on MR board even directly. As you say, a lot of things are just manufacturers cross promoting their products as a MUST USE!!

Cheers again.