Plastering over Thermal plasterboards

[Simon Fuller]

Hi,
inexperienced plasterer here - I'm about to do a little project boarding and plastering an outhouse. I am going to use thermal plasterboard, just to help keep the outhouse a little warmer. It will most likely be Knauf XPS Laminate Plus board, the 27mm version.

My question is, when it comes to external corners, around the door and window reveals, how should I do this?
I will obviously have thin strips of plasterboard to do the reveal parts, but if I do it all using the thermal plasterboard, then unless I do some kind of complicated mitre cut, there will be part of the insulation visible at the edges. I will be using angle bead, which will partly, but probably not completely cover it. I dont know how the plaster will stick to the insulation.

So, should I:
Just do it like that - the bit of insulation showing won't matter?

Do it like that and put a thin coat of bonding over the visible insulation before I plaster?

Attempt some kind of mitre cut?

Use non thermal plasterboard for the reveal parts - it solves the problem of the insulation showing, although will slightly reduce the effective-ness of the insulation as a whole?

Something else?

Any help and advice much appreciated!!

Simon

 

[vinn]

As an inexperienced plasterer you might run into a number of unforseen difficulties using insulated board - or any Dot & Dab if it comes to that.

FWIW: skim bead is used with p/board - angle bead is for solid.

 

[Simon Fuller]

Thanks for this.
I'm not actually planning to Dot & Dab, I'm going to batten the wall. I know most people would probably dot and dab, but I feel more confident with the batten method, and it certainly makes the corners easier!
Any thoughts on how to deal with the corners?

Also - regarding beading - planning on using 'thin coat angle bead' which as best I can tell from googling is what you are referring to as skim bead? It says its on the blurb that its meant for plasterboard.

 

[vinn]

You could deal with the corners as you suggested above, no mitre cuts but a 12mm piece in the reveal.
What you have to consider with battens & insulated board is pulling out the reveals too far.

But you might be best advised to get a plasterer in for a paid for heads up on site. There could be too many variables to go into on here.

 

[Doggit]

The trick on the reveals, is to cut back the insulation on the wall run, to allow the reveal piece to set back into it, so if you're using 27mm plasterboard and insulation, then you'd cut the 27mm of insulation away, plus a little bit more for the D&D adhesive. If you don't mind wasting a bit, then cut away 35mm of insulation, and then trim off the excess plasterboard once the reveal piece has gone in.

 

[Simon Fuller]

Hi. Thanks both of you. Cutting back the insulation makes sense. although I will bear in mind the comment about making the reveals too big. Before I cut anything I'll measure carefully, and if its unlikely to fit I could use standard plasterboard rather than insulated to gain back the space.

 

[Doggit]

Consider hacking off the plaster in the reveal if necessary, otherwise you'll get a cold spot in the room that will risk getting condensation and mould.

 

[Simon Fuller]

There is no plaster there at the moment. Its a single skin brick wall with a window and a door. So unless I have misunderstood you, its either going to fit or its not. I think it will fit though, as there is effectively no reveal at all at the moment, I will be creating it from nothing.
(I'm aware that this amount of insulation isn't going to make a massive difference on a single skin brick wall, but its more of an exercise. The outhouse doesnt really need to be insulated at all, but every little helps, and it doesnt matter if it doesnt look amazing. I'm doing this as much for the practice if anything, to decide if I trust myself enough to attempt plastering some rooms inside my own home!)

 

[Doggit]

If there's pretty much no reveal, then there shouldn't be much of a problem. Good luck, and post some pictures when you've done it.

 

[phatboy]

If there is no reveal, just use insulated board to 12.5mm from where you want to finish, and then attach a piece of bare board?

If there is a bit of reveal, maybe get a sheet of thin insulation and fit that, or slice it in half to make even thinner, then stick the plasterboard over it?

 

[foxhole]

I used fixing foam throughout , builder was sceptical as he had only ever seen dot and dab but was so pleased with result has used foam fixing himself.
Very quick and easy .

 

[phatboy]

I used fixing foam throughout , builder was sceptical as he had only ever seen dot and dab but was so pleased with result has used foam fixing himself.
Very quick and easy .

Did you add any mechanical fixings afterwards? Or was the foam alone enough?

 

[foxhole]

Used a few fixing at first , but towards the end proved so reliable needed little in the way of fixing.