Can you paint straight onto MR Plasterboard (or is a sealer/primer needed)?

[Oxbow16]

Hi all

 

I'm going to be putting up some MR plasterboard on the bathroom ceiling today.  There'll only be one or two joins, so I won't be having it skimmed (that being said, I've read in places that you shouldn't skim MR plasterboard anyway).  

 

What I don't know is what prep the MR PB needs once up?  I've done some reading on the subject and there's a whole load of different opinions and answers.  So I wondered if anyone here can set me straight please?  Does it need a sealer?  A primer?  Or just paint straight on?  

 

In case it makes a difference, the room is part ceiling part skeiling, so I will be looking to use plaster or whatever to round off where the two boards meet.

 

Many thanks

[JohnMo]

Water down normal emulsion about 20 to 25% for first coat, same with all plasterboard.

[nod]

MR board is fine skinned 

It’s more the joints that need sealing 

 

[Oxbow16]

3 hours ago, JohnMo said:

Water down normal emulsion about 20 to 25% for first coat, same with all plasterboard.

 

I read that elsewhere and must admit to being a bit confused by it.  I understand the need for a mist coat on standard plasterboard and skimmed walls, because they are absorbent.  But if MR is - as the name suggests - resistant to moisture, then presumably it's less absorbent and less in need of a mist coat to "soak up"?  Or am I missing something?  

 

3 hours ago, nod said:

MR board is fine skinned 

It’s more the joints that need sealing 

 

 

This is also something I read mixed opinions on.   Some people seem quite adamant that if you skim it you're completely nullifying the point of using it in the first place.  I think their argument is that it would be like wearing a moisture resistant coat, then putting a cotton or wool jumper over the top of it.  That being said, whatever the answer I won't be skimming so all I really need to know is what the MR board needs before painting.  

 

Many thanks to you both for your replies.

[JohnMo]

A mist coat is watered down emulsion. Take emulsion add 20% water mix well, paint/roll as you normally would.  Next coat full strength emulsion.

[nod]

Any boards that are being taped should alway have a gypsum primer on them 

[Oxbow16]

OK, thank you both    

 

So is this a case of two different opinions/options?  Or use a gypsum primer AND mist coat?  Or are you classing a mist coat as a gypsum primer?  

 

Still a bit confused by the options!  

 

44 minutes ago, JohnMo said:

A mist coat is watered down emulsion.

 

Thanks, I'm familiar with mist coats and have used it on bare plaster before several times in the past.  I've just not used MR PB up until now so don't know what is needed for that in particular.  And I'm still struggling to understand my a mist coat on a board that is designed to resist moisture; although I'm equally happy to accept that could be just my thinking going awry!  

[nod]

I’ve forty years experience as a taping and plastering contractor Don’t paint directly onto to Plasterboard 

[Oxbow16]

19 hours ago, nod said:

I’ve forty years experience as a taping and plastering contractor Don’t paint directly onto to Plasterboard 

 

No worries - I won't!  

 

Can I use Zinsser Bullseye 123?  I already have some so it would save a shopping trip, and it is only a small area.  Plus, it's nice and thick and I would rather use something that isn't runny/messy as some of the lower sections of the room have already been done (don't ask!).  But is it suitable?  

 

Many thanks