Insulating plastered rooms with insulated plasterboard

[dobson156]

Hi, I have a house with a cavity wall which currently has plaster applied directly to it.

The house is quite old and I live in a very wet area do I do not fancy my chances with the sort of insulation that is pumped into the cavity.

What I'd like to do is use insulated plasterboard on the walls that are on external walls.
I am really not a fan of dot and dab, so my plan was to knock off the current plaster (which I imagine is going to be a massive pain), stick up battens and then secure the insulated plaster to them.

1. Does this sound like a good idea?
2. Is there are good way of removing the existing plaster from the block work - I also fear they might be thermalite blocks.
3. what width plasterboard should I be looking at to actually make a difference? I was think 25mm batten + 50mm insulation. But thats starting to eat quite a bit into the room.

Thanks

 

[foxhole]

Unnecessary work , just glue to existing with fixing foam . 50mm insulated boards so 62mm over all then skim.Add a few mechanical fixings , I used 200mm screws into thermalite .

 

[cdbe]

I'm interested. I also dislike the ideal of foaming them on. Maybe look into the fixings used for EWI, I think some kind of plastic hammer fixings through the old plaster and into the blockwork. If you hack off the plaster it will be hard to fix the battens plumb if the blockwork is uneven.

 

[Deleted member 174758]

If you hack off the plaster it will be hard to fix the battens plumb if the blockwork is uneven.

You fix through packers. Piece of cake.

 

[dobson156]

You fix through packers. Piece of cake.

I assume by this you mean shim out the battens so that they're plumb? That's what I've done before on a wall that isn't remove flat.

Sticking the board up directly to the existing wall is easily the quickest way, but I really don't like using adhesives and it just seems to store up problems down the line as well as chewing into the room. I like that with battens I have evenly spaced points where I can attach things to the wall - its more work but it just seems like a better engineered solution.

 

[foxhole]

I assume by this you mean shim out the battens so that they're plumb? That's what I've done before on a wall that isn't remove flat.

Sticking the board up directly to the existing wall is easily the quickest way, but I really don't like using adhesives and it just seems to store up problems down the line as well as chewing into the room. I like that with battens I have evenly spaced points where I can attach things to the wall - its more work but it just seems like a better engineered solution.

How does adhesive ( few mm) chew into room space compared with 25mm baton.?

 

[foxhole]

I'm interested. I also dislike the ideal of foaming them on. Maybe look into the fixings used for EWI, I think some kind of plastic hammer fixings through the old plaster and into the blockwork. If you hack off the plaster it will be hard to fix the battens plumb if the blockwork is uneven.

Hammer fixing pull straight out if thermalite blocks , as mentioned .

 

[Deleted member 174758]

I assume by this you mean shim out the battens so that they're plumb? That's what I've done before on a wall that isn't remove flat.

Yes. Precisely that. Using either glazing packers or horseshoe packers:

But against using a low expansion foam it is a LOT of work and the advent of low expansion foams has made the technique almost obsolete

Sticking the board up directly to the existing wall is easily the quickest way, but I really don't like using adhesives and it just seems to store up problems down the line as well as chewing into the room.

TBH I don't see what the problem with using foam is. The type of foam used should be the low expansion stuff (like Soudal Plasterboard Adhesive Foam) which is used as a replacement for dot and dab and for fixing skirtings, not the old high expansion foam. Your space loss is a few millimetres, no more:

As with any product like this you do have to ensure that the wall is relatively dust free before you start, but that's fairly obvious, I'd have thought

 

[mrrusty]

If its an old house it's likely the walls are not mega flat. Foam is great on flat walls but if fixing insulated pb to bumpy brick use dab adhesive. I used siniat board and this is their recommended method.

I never get the batten thing. If the walls are not flat the battens won't be flat. Dabs allow you to set the pb to a nice flat surface. Dabs give much more scope for knocking into place than foam. I used both in latest house refurb. 72mm insulated pb on all exterior walls where possible. Thinner where not.

 

[Deleted member 174758]

I never get the batten thing. If the walls are not flat the battens won't be flat.

You fix a batten at either end of the wall, packed off the wall to get each one dead plumb. You then run three string lines between them (top, middle and bottom) and work to the string lines for the remaining battens, packing as needed. It's straight forward enough, but as a technique it is pretty old hat and there are faster ways of doing things these days. It's similar to how you'd build an MF framework using resillient bars, but I doubt anyone here wants to get involved with MF (which I actually like as it is fast and accurate)

 

[Deleted member 292770]

the concept of ‘fixing a pb to a wall’ with a mechanical fixing is nonsense.
and the bigger the fixing the more nonsense it is. once you drill a pb there is literally no strength at that point making a poxy screw a complete waste of time and money.

 

[Deleted member 292770]

id grit the wall first using plasterers primer. (green grit). then dryline directly with thermaline board using gtec universal pb adhesive. or solvent free foam if the wall is flat enough.