Thick insulated plasterboard at first fix

[comptonspark]

Looking at a rewire on an old cottage and just discovered that the walls are to be lined with an insulated plasterboard which is about 65mm think, so when fitted to the wall I guess 75-80mm from finished surface to original wall.

I was wondering how best to do the first fix since normal 25-35mm back boxes on the original wall will be too far back and i don't really want to use (very) long screws in the sockets!. Previously I've used drylining boxes with this sort of insulating board, but that was on stud walls so I could easily locate the cables in the void afterwards.

any suggestions?

thanks - Michael

 

[Tim M]

Find out from whoever is doing the plastering how the boards will be fixed - mechanically to 2x1 battens or dot & dab, then you can work out the finished depth from the wall. Rip some 3x2 down to the right thickness( best make it a little less ) to bring your boxes flush and cut to length and screw these to wall and then your sockets to these. Ideally your bits of timber should be treated and have a piece of dpc behind. Or, of course use dry-lining boxes.

 

[Steve_P]

Always used dry lining boxes on this sort of job.

 

[Rockingit]

The board will almost certainly be fixed on battens which means you'll have 20-30mm void to drop cables down, leave a sufficient loop to be able fish them out, remember where you left them, use a template to cut a hole for a dry lining box (multi-tool or fein is brilliant for this), reach in, grab cable, problem solved. You'll need to go off-piste a bit and carve out the foam from either side of the hole or the lugs in the boxes wont retract and tighten properly. I must have done about a 100 or so in one property using this exact method earlier this year, takes seconds after you've done a few for practice.

You can also just clip the cable down the original wall which keeps it away from the insulation part. The bonus is that you're already way below the 50mm rule so you can be a little more generous with your zones if you need to.

 

[yellowvanman]

Always used dry lining boxes on this sort of job.

Yep, I also try and avoid cable contact with the insulation and put cable in oval tubing. I know modern materials should not react with the PVC but just to make sure!

 

[Steve_P]

Yep, I also try and avoid cable contact with the insulation and put cable in oval tubing. I know modern materials should not react with the PVC but just to make sure!

Modern no, there's a lot of lime plaster in the refurbs round here . . . . .

 

[Farmelectrics]

try and be there when they board it and get your cables into place that day dry line boxes

 

[Silly Sausage]

try and be there when they board it and get your cables into place that day dry line boxes

Good suggestion! So they can skim them in (so that horrible plastic flange doesn't show)

 

[Stroppy]

carve out the foam from either side of the hole or the lugs in the boxes wont retract and tighten properly.

A tack lifter is the idea tool for parting the foam from behind the plasterboard, with its cranked head to get 'round the corner'

I bought mine specifically to do this, and have never actually used it to lift tacks!

BTW, thick insualted plasterboard is known as "thermaboard".

 

[Colsey c]

I always use dry line boxes for peace of mind on this sort of job, builders have a habit of saying one thing.... Yeah it will be 40 mm deep and when you come back its doubled or worse left your boxes sticking out proud!!!!
As said before about protecting cables from insulation