No wood, or strapping, use sheet insulation and adhesive or foam

Reading up on this on historic Scotland would be a good move.

I agree with Pile-o-Stone, if your stone is not so uneven that you can't dub it flat. I had rather assumed, with the wedges and all, that it might be just too rough. Remember, if you have dubbed out a lot and use 100mm boards, you need some pretty long fixings.

With a bit of practice and a sponge, you don't even need to get the country cottage look. I am definitely not a plasterer, but get a very good finish with the Baumit plasters. *Much* easier than gypsum, but much slower, too, which is frustrating for small areas (though not so bad if it is your own house - more of a bu**er if the job is 25 miles away!).

A general point worth remembering with rigid wood-fibre - If the walls are badly 'bent', 100mm won't take a bend, but 40, 40 and 20 will. I did a very 'bent' wall in Derbyshire that way. More bridging because of more mech fixings, but a relatively small price to pay.

I'm late into the discussion but wonder if you considered hempcrete, Westie? I've just installed 80mm pavadentro in my bathroom but hadn't accounted for the fact that the walls were actually plastered with cement, not lime as I'd thought when I ordered the insulation. I therefore had to take off all the cement and it was v hard to level the walls - not being a plasterer myself. I'm sure I've ended up with air gaps behind the woodfibre which is not brilliant. I'm about to use hempcrete to insulate the living room and am dealing with similarly uneven walls - just Victorian brick but pretty uneven. I think - and can report back later - that hempcrete will be a better solution as it moulds to the walls rather than having to dub out or otherwise flatten off.

+1 on troweling, especially with the thickness you'll be doing with hempcrete.

I was just wondering what the difference in cost and thermal performance would be with hempcrete vs fibreboard for the same thickness? I will be moving onto the next room shortly and I'm happy to change products if the results would be superior (I've used 100mm fibre boards).

The only thing putting me off would be the amount of effort in building the shuttering than just drilling and hammer fixing the boards, but if a little more effort yields better results then I'm happy to do it.

Breath-ability has been mentioned here with no mention of air-tightness which is 99 times more important.
If Pavadendro is badly fitted with gaps where the boards meet the floor/ceiling and each other then you'll have similar condensation problems on the outer wall as with insulated plasterboard.
If insulated plasterboard is fitted correctly in an airtight manner with expanding foam at the floor + ceiling and between boards then there will be no moisture present where the board meets the wall to condense. To eliminate air-movement behind insulated plasterboard use expanding foam around the perimeter and a few lines horizontally, this eliminates the need to level the wall. Dampen the wall before you stick Ins P'board to it, it improves adhesion and helps the foam to go off. If there's any hollow sections behind a sheet of Ins P'board, drill a hole, stick in the nozzle and fill with foam.
There's never been a documented case of structural decay in a building resulting from water vapour diffusion!

Posted By: Pile-o-StoneIsn't spalling an example of structural decay in a building resulting from water vapour diffusion?

More usually caused by rain soaking in from outside and freezing, I think.

Posted By: Viking HouseBreath-ability has been mentioned here with no mention of air-tightness which is 99 times more important.
If Pavadendro is badly fitted with gaps where the boards meet the floor/ceiling and each other then you'll have similar condensation problems on the outer wall as with insulated plasterboard.
If insulated plasterboard is fitted correctly in an airtight manner with expanding foam at the floor + ceiling and between boards then there will be no moisture present where the board meets the wall to condense. To eliminate air-movement behind insulated plasterboard use expanding foam around the perimeter and a few lines horizontally, this eliminates the need to level the wall. Dampen the wall before you stick Ins P'board to it, it improves adhesion and helps the foam to go off. If there's any hollow sections behind a sheet of Ins P'board, drill a hole, stick in the nozzle and fill with foam.
There's never been a documented case of structural decay in a building resulting from water vapour diffusion!

Bauwer Insulation is the alternative to insulated plasterboard being highly vapour permeable solution, easy to install and achieve air tightness as well. You could see the application process at:

https://youtu.be/oxogp2uRgaw

Posted By: WestieI recently started stripping off the lath & plaster in one of my bedroom walls, with the intention of installing wood fibre insulation batts between the framework that the laths are nailed to, and re-boarding with plasterboard.

Historic Scotland would have said fill the void between lathe and wall with EPS beads and leave the wall intact.