Fixing insulated plasterboard - general advice

[JP_]

OK, so next job is to fix insulated plasterboard to this wall.

It's 250 high, so I'm thinking that 240*120 sheets vertically, supported by about 10cm of leftover insulation board, would be just the ticket. The skirting will cover the insulation board. I'd just need to cut one board.

Which is the tricky bit. After having a nightmare cutting chipboards with my circular saw (Worx, tried 2 blades, thing just got bloody hot and smoked) I went back to my trusty old jigsaw. Are there any recommendations for insulated plasterboards for ease of working with - less interested in best price or best thermal properties if there's one that is easier to handle than the rest!

 

[Ian H]

They will cut very easily with a saw.

 

[JP_]

ta.
so, any reason to go for a more expensive brand? Seeing some boards for about £20, 9.5mm plasterboard and 20cm insulation.
Sound reasonable?

 

[Ian H]

How are you fixing it to the wall?


There are boards backed with PIR and others backed with polystyrene looking stuff. I'd imagine the PIR is better and more expensive. I used separate PIR and plasterboards which worked out cheaper but that was easy because I screwed them to timber.

 

[JP_]

I'll be using adhesive to stick in on.

 

[Ian H]

I'm not sure then. I've only ever dot'n'dabbed normal plasterboards and screwed insulation with boards over.

 

[endecotp]

any reason to go for a more expensive brand?

Polystyrene, used on the cheapest boards, is a much less good insulator than PIR or phenolic insulation used on the others.

Seeing some boards for about £20, 9.5mm plasterboard and 20cm insulation.
Sound reasonable?

Do you really mean 20cm, or 20mm?

What are you trying to achieve, thermally?

 

[JP_]

Mm, sorry. Main objective of too just make it a bit warmer and reduce condensation risk, as well as get a nice new wall finish.

Have ordered some cheap boards and adhesive. On a tight budget .

 

[oldbutnotdead]

Builder I used glued 12.5mm sheets of plasterboard to 70mm Celotex (foil both sides) with non-solvent Gripfill, then dotted and dabbed the whole assembly to the walls. Feels solid, hasn't fallen off yet......

 

[Doggit]

Did the same trick about 12 years ago, and it's still up there. Nowadays, I'd add a few mechanical fixings as well though.

 

[JP_]

OK, bought this stuff: https://www.mkmbs.co.uk/prodb001892...terboard-2400mm-x-1200mm-x-30mm-tapered-edge/
along with some Everbuild DRYFIX7 PINKGRIP DRY FIX

Should I also fix with screws into the bricks, or will the adhesive be enough? If so, what sort of screws?

 

[mwatsonxx]

For fire protection, it should also have mechanical fixings, nine per board.

 

[JP_]

what sort of fixings are those? something specific, or just screws into masonry rawl plugs?

 

[endecotp]

If that's a solid brick external wall, adding 20mm of polystyrene will reduce heat loss from about 2.2 W/m2K to about 1.0 W/m2K, i.e. you will approximately halve the heat loss through that bit of wall. Not a dramatic difference but worthwhile.

Your boards cost £30. For £25, you could have got 25mm of PIR - about twice as insulating: https://www.secondsandco.co.uk/product-page/plasterboard-laminate-25mm-12-5-straight-edge - but for small quantities, delivery costs dominate.

You need some mechanical fittings so that the boards don't fall of the wall and block your escape route in a fire (the polystyrene could just melt). Two or three along the top of the board might be enough but check what the board manufacturers recommend. I'd probably use frame fixings like e.g. https://www.screwfix.com/c/screws-nails-fixings/frame-hammer-fixings/cat840010 because you can fit them after gluing, but they're expensive if you have to buy a box and only use a couple, so anything like a rawlplug and screw (if you can line it up) or a masonry screw would be OK.

 

[JP_]

Yeah, I did look at the PIR boards, but on a tight budget and really cannot afford to spend more than £100 right now. An improvement is the main aim, with reduced risk of condensation to stop mould etc. (which is mostly under control with new ventilation). It's a bedroom, so I always think, matter less if a bit cooler!