Installing insulation backed plaster board.

[Marcusjfrancis]

In my 1930s house I would like to install some insulation backed plaster board to the external walls to add some warmth.

The walls have a cavity and there is no issues with damp.

I have seen a lot of people just foaming the back and laying the boards straight on to the brickwork or existing plaster.

My concern doing this is that, currently the internal skin is a warm wall, kept warm by the inside temperature. If water vapour from indoors travels through this wall it will then condense when it meets the cold exterior skin. Which isn’t an issue, but if I add insulation onto the internal skin, the internal skin then becomes the cold wall. If vapour travels past the insulation and touched the cold wall behind it the vapour will turn to condensation and will surely be trapped between the brickwork and insulation causing damp?

Has anyone had issues doing this before or could shed some light on why this wouldn’t be an issue?

 

[foxhole]

Moisture cannot pass thru insulation and there is no air gap to allow condensation.
Your internal wall is never warm enough to prevent condensation, especially during winter , only ventilation prevents it.

 

[Marcusjfrancis]

Great, thanks for your reply.

So I should be pretty safe to just stick the board straight on to the brickwork then and plaster?

 

[mrrusty]

I wouldn't fix to existing plaster if it is in any way unsound. Depending on how flat the brickwork/surface is, you may find using dab adhesive is better than foam. Foam is great when the surface is very flat - it compresses to almost nothing. be aware it will push out a little as it sets, so a few screws/plugs can help to keep everything in position and lined up.

If the wall is not flat IMHO you are better using dab adhesive. This will nominally be 10mm thick, but because it is a much firmer adhesive, it allows you to knock the boards in to position, level with each other and they then don't move about while setting - the adhesive will easily take out any humps and hollows in the surface.

If your cavity is ventilated, then any condensation that occurs in the internal brickwork will evaporate into the ventilated cavity.

I've done this on our house (1902 with 50mm cavity) with no issues.

 

[foxhole]

I used foam adhesive on all my walls , about 30 insulated boards , apply foam to board , wait 30secs and then press into place, there no further expansion and the foam flattens as it’s pressed home , then added a few mechanical fixings.