Insulated plasterboard: 15mm PIR + 6mm Magply - any issues

[bmj1]

Hi all,

 

We need to dryline our walls (cavity construction, concrete inner skin, brick outer) to bring up our u-values.

 

I'm trying to keep the wall build-up minimal.

 

I've found a company who can bond 15mm of PIR to 6mm Magply, which we can then dot + dab on.

 

I'm not familiar with plasterboarding / MGO alternatives, has anybody here used Magply? Will I be okay with a 6mm thick magply for my walls ?

 

Any other issues/concerns to flag up ? I guess hanging joinery (e.g. in kitchen) might need to be fixed all the way through to the concrete substrate ?

 

Thank you so much in advance.

 

[Conor]

Sounds like an expansive build up. Why not just 40mm insualted plasterboard straight on to the blocks?

 

15mm PIR, 6mm magly, 10mm dot and dab, 12.5mm PB = 43.5mm minimum.

Edited May 23, 2023 by Conor

[bmj1]

2 hours ago, Conor said:

Sounds like an expansive build up. Why not just 40mm insualted plasterboard straight on to the blocks?

 

15mm PIR, 6mm magly, 10mm dot and dab, 12.5mm PB = 43.5mm minimum.

 

Hi Conor - my thinking was the Magply is instead of PB. Does that make sense ?

[bmj1]

I.e. that's a build up of:

 

10mm dot+dab + 15mm PIR + 6mm Magply + 3mm skim = 34mm

 

Plasterboard is of course thicker than the Magply

[JonBATConsult]

What are you dabbing it onto? 

[bmj1]

Just now, JonBATConsult said:

What are you dabbing it onto? 

 

Concrete blocks.

 

So the third party company will bond the PIR onto the Magply for us, and then we do the dot/dab of the combined product and skim.

 

Does that make sense?

[RobLe]

I’ve used 9mm magply, it’s great stuff, water resistant, fairly tough.  Mechanically similar to the same thickness of plywood.  The easiest way to cut it is score it to cut through the glass mesh and snap. Seems a lot of faff for 15mm of pir mind.  I used it as floor, does plaster skim stick to it ok?

[bmj1]

10 minutes ago, RobLe said:

I’ve used 9mm magply, it’s great stuff, water resistant, fairly tough.  Mechanically similar to the same thickness of plywood.  The easiest way to cut it is score it to cut through the glass mesh and snap. Seems a lot of faff for 15mm of pir mind.  I used it as floor, does plaster skim stick to it ok?

 

I'll call them in the morning and ask how we skim it.

 

I guess my alternative question is if anyone is aware of a very strong, thin plasterboard / plasterboard alternative ? (that could be bonded to the PIR instead of PB)

Edited May 23, 2023 by bmj1

[JonBATConsult]

Is this a new build or refurb?

I've been working in Building acoustics and air permeability design and testing for 15yrs so youve got the right person.

I see what you are trying to do BUT if something happened, fire etc and the board delaminated all parties would wipe their hands clean of you. I would recommend buying a purpose made board, i looked into doing this on my own diy project but I found buying a standard board ended up being better. 

To maximise the thermal improvement i strongly reccomend sealing the blockwork prior to installing the insulation. Makes a huge difference in Airtightness. This can be done using a really thin render or pargecoat (even roller it on).. I did this on my own house before insulating and I have a permeability of below 2m3/hr.m2 which is fantastic! 

Edited May 23, 2023 by JonBATConsult

[JonBATConsult]

Regarding plaster i bet that board will suck like crazy on the first coat. Prime prime prime