Fixing plasterboard to IWI

[Hammertime]

I've got hollow cavity walls, internal leaf is thermalite. I've stuck 50mm PIR to it with PU adhesive, and I will use the same to attach plasterboard to the PIR, but I think I need some mechanical fixings through to the thermalite too.

What would people recommend?

- Twistfix make one but it's metal and they say it can cause thermal bridging.

- There are hammer-in fixings but again, the only thermal break is a thin piece of plastic and the screw is metal

- There are some plastic plugs with fibreglass pins to nail in like the Fischer DIPK, which is probably what I'll use if there's no better option - only problem is the disc heads are about 3mm thick, so skimming over could be an issue.

 

Is there anything more suitable that you know of?

 

Thanks

 

[Russell griffiths]

How are you running services, you could run a service batten on top of the insulation then fix plasterboard to that. 

[Mattg4321]

Why didnt you use plasterboard that comes already attached to the PIR out of interest?

 

I'm not sure there's any approved method of using mechanical fixings into masonry to fix plasterboard.

[Hammertime]

Thank you both. That could be an option, @Russell griffiths - I've generally tried to avoid running services on those walls eg putting sockets on internal walls where possible. My concern would be that I still need to pierce through the insulation to the thermalite in order to fix the battens and the plasterboard would be on top of those screws, so it's whether the margin of benefit would be worth the extra space lost. 

@Mattg4321 I decided to go that route partly for cost (it was much cheaper buying them separately) and partly because I can then foam and tape the PIR so the insulation and its foil facing are both continuous, which I thought would be harder with combined insulated plasterboard. 

There are some plastic plug and pin fixings here on insulationuk that look similar to the Fischer dipk ones, but it specifically says it's not for insulated plasterboard. I wonder why that is? I phoned them and couldn't get a definitive answer. Maybe because the disc is 3mm. If so, could I recess the disc slightly in the plasterboard then scrim over?

[Mattg4321]

6 hours ago, Hammertime said:

Thank you both. That could be an option, @Russell griffiths - I've generally tried to avoid running services on those walls eg putting sockets on internal walls where possible. My concern would be that I still need to pierce through the insulation to the thermalite in order to fix the battens and the plasterboard would be on top of those screws, so it's whether the margin of benefit would be worth the extra space lost. 

@Mattg4321 I decided to go that route partly for cost (it was much cheaper buying them separately) and partly because I can then foam and tape the PIR so the insulation and its foil facing are both continuous, which I thought would be harder with combined insulated plasterboard. 

There are some plastic plug and pin fixings here on insulationuk that look similar to the Fischer dipk ones, but it specifically says it's not for insulated plasterboard. I wonder why that is? I phoned them and couldn't get a definitive answer. Maybe because the disc is 3mm. If so, could I recess the disc slightly in the plasterboard then scrim over?

I understand why you did this, as I also did the same. That insulated board is impossible to detail properly in my opinion. 
 

I fixed it slightly differently to you though. I didn’t stick the PIR. I fixed through 18mm thick battens (then through the PIR) into the blockwork and then screwed plasterboard to the battens. 

[torre]

If your insulation is already stuck and you can't change course then maybe an insulated fixing but with the built in washer cut off and replaced with something thin and galvanised to plaster over like this?

 

You'd need the insulated fixing's pin to have a bit of a head on it, which not all do (I've used EJOT before and some of theirs do).

 

It's also worth asking fixing manufacturers technical support for suggestions. 

 

If you can put up with the thermal bridging then those galvanised flat washers with any kind metal hammer fixing would be effective too 

[Mike]

I'd guess that the weak point is likely to be the junction of the insulation and the wall, not the plasterboard to the insulation; the wall is unlikely to be perfectly flat (so the bonding patchy) and the surface might be friable. So, if I was concerned, I'd add some mechanical fixings before fixing the plasterboard.

 

Edited 20 hours ago by Mike

[Hammertime]

That sounds like a great idea, @torre - I bought some stainless steel washers recently so if I could fit those instead then it would solve my problem. Only issue might be getting the built-in plastic disc off, as I haven't seen any plugs where the disc is separate, but I will keep looking.

 

Thanks @Mike - if so then I could maybe countersink the discs into the insulation for a flat surface to stick the plasterboard on to. But would the foil face of the PIR come away under the pull of the plasterboard if using pu adhesive alone?

[Thorfun]

Service cavity with battens for me every time. Would make mechanical fixing of the plasterboard simple. It’s what we did. Can’t imagine avoiding running cables on every external wall. I could guarantee I’d need a plug socket on them. 

[Beau]

This is how I did our bathroom. 50 PIR bonded to wall with plasterboard PU foam. Then used the foam to fix the plasterboard to the PIR. Drilled through the whole lot with a 5mm masonry drill bit. Used long plasterboard screws (larger heads) with the yellow plugs to fix it back in a few places. If the head of the screw was going to pull through the paper I would use the large stainless washers already mentioned. I dont see that much extra fixing is required as the top is locked into the ceiling when it's all skimmed and the weight is resting on the floor.

 

I tested the bond strength of the PU foam with a small  piece of PIR and the lime plaster came off my walls before the foam failed