Sealing and painting interior stone wall

[CraftyMagpie]

We have an old stone house (over 150 years) and I'm fixing some areas of damage to the interior paint, beneath which I'm finding a little discoloration here and there, though perhaps not actual damp. I've like advice on how to stain block and repaint without preventing the walls from continuing to breath. The existing paint is likely mineral-based, from its chalkiness where I'm removing all the loose bits. The plaster below is also chalky so probably lime render (I'm no expert) and quite old, and has a little pale yellowing here and there towards the floor, and slight pink edging at one corner. What would be a good product to use to stain block the old plaster before I apply a new mineral-based top coat? I understand that I should not use an acrylic based sealer as that would prevent breathing.

 

[Bonni]

Solid walls need to breath, try sealing them on either side with modern paints, cement, renders, Thompsons water seal etc.. and you will enter the world of problems.

In the day they were built, lime mortar was used, white wash was chalk based, and interior emulsion was clay based. The sealant around openings was burnt mastic. Windows etc.. used to allow gales to blow through, thus plenty of ventilation. Even then, solid walls were never 100% damp free, the moisture has to go somewhere, and breathes out of the wall.

I would just paint with a breathable applicable paint that your local paint retailer will be able to advise on.

 

[CraftyMagpie]

Thank you. Would you also happen to know of a safe modern breathable plaster to fix small holes in the old plaster, and a breathable stain blocking application prior to the top coat breathable paint?