Internal insulation for salt-contaminated walls

[MDE]

I have a room with two outside walls (rubble stone construction with render outside). Both appear to suffer from salt contamination. In a previous era, I think it was used as a larder for salting pork etc. There is no obvious sign of dampness. I have tried many things to fix them including complete replastering, but the new plaster eventually crumbles and falls away (I should add that I have plastered many walls in the house with no difficulty). One area where I coated over the lime plaster with DG27 (from Mike Wye) has fared better but now, some 16 years later, that too is starting to deteriorate.
I am proposing to add a solid insulation layer and then plaster over that, but the room is small so I don't have much opportunity to add a thick layer and because of (rather nice) window cills etc. I am limited to a thickness of 35mm.
Any suggestions?

 

[a twig]

I’d suggest 15mm (or 25mm) wood wool board mechanically fixed to the walls and then skimmed with lime as per here, or wood fibre as per @CarolineTheChemist posted in the next post in the same thread

https://www.periodproperty.co.uk/forum/threads/plastering-question.16738/post-243367

 

[Lacan07]

I have a room with two outside walls (rubble stone construction with render outside). Both appear to suffer from salt contamination. In a previous era, I think it was used as a larder for salting pork etc. There is no obvious sign of dampness. I have tried many things to fix them including complete replastering, but the new plaster eventually crumbles and falls away (I should add that I have plastered many walls in the house with no difficulty). One area where I coated over the lime plaster with DG27 (from Mike Wye) has fared better but now, some 16 years later, that too is starting to deteriorate.
I am proposing to add a solid insulation layer and then plaster over that, but the room is small so I don't have much opportunity to add a thick layer and because of (rather nice) window cills etc. I am limited to a thickness of 35mm.
Any suggestions?

The traditional method of dealing with salts on chimney breasts (where the soot and lime mortar has reacted) was to add fresh cow sh*t to the scratch coat. I wonder off this might have helped when re-plastering?

 

[housewinnie]

Could you leave the walls as is without plastering. Maybe hang the odd carpet rug etc

 

[MDE]

Could you leave the walls as is without plastering. Maybe hang the odd carpet rug etc

Well, I'd have to remove all the old plaster and I suspecyt apart from not adding insulation, the rugs might go mouldy as the walls are cold.

fresh cow sh*t to the scratch coat

Plenty of that around just now, with cattle in the sheds, but I'm not sure the missus would approve (plus I'm not sure of the insulating value of cow sh*t)