Painting inside my stone shed

It may be the inside of a damp wall so my comments may still apply... "sealing" is probably going to be impossible unless it's cavity walled & dpc'd ?

YMMV

The same shed I am fixing up. Stone and rubble walls, pretty rough. I thought I would paint the insides white. Obv there is plenty of damp coming up from the ground. Someone told me that if you don't want to do limewash you can paint the inside with exterior masonry paint - that it's breathable and won't peel off. Is that so? Any exterior paint? Tim W

TimW was thinking very hard :

The faces of some rustic faced bricks, surrounding my front door (outside), I had the faces blow of the two courses at the very bottom. I spent quite a long time wondering how to repair these and finally settled on making good the damaged faces with sand and cement. All of the faces of the bricks around the door were likewise, quite delicate, though only the bottom ones were actually blown. I settled on painting them with exterior masonry paint, working it well into the brick faces.

That was several years ago and it has worked absolutely fine. It has acted as a sort of glue, to reinforce the loose brick surfaces and prevent further weather damage. This year I spotted two 1" square sections where the paint had lifted, so I patched them.

The door faces west and gets the very worst of the sun and rain, indoors it should last much longer.

It's inside. It's all dusty, crumbly, spidery mortar and stone so I need to put some kind of coating / seal over it and make it nice and cleanish.

TW

on 19/06/2020, TimW supposed :

I thin watery coat of Thistle plaster will help stabilise the surface, applied with a large brush.

Usually looks like dandruff after a couple of years. I wonder if that wall coat we had put on our walls might be a solution but the prep is a bit of a pig, with some kind of sealant then undercoat then the plastic coating. It has been very good, I have to say. Brian

Painting it with lime would sort that just fine. It's way more breathable than masonry paint. Just mix builder's lime with water to make paste, dilute 50/50 and paint on. Don't try to overthicken it to compensate for its thin appearance, it bodies up twice during drying & curing.

You talk of breathable and sealing, the 2 are of course opposites. If a wall is damp, sealing it will make the damp worse.

NT

Is this 'builders lime' ? It doesn't say to paint it on.

For painting with lime see:

and

Limewash and Distemper are vapour permeable and allow the building to ?breathe? and are therefore suitable for use in traditional buildings, and particularly appropriate for the decoration of porous building materials ? lime plasters and renders, limestone, soft brick, cobs and daubs.

When properly applied to appropriate surfaces, they do not dry with a powdery finish and do not readily brush off on clothes.

Traditional paints are made with natural sustainable ingredients and are environmentally friendly products containing no VOCs, lead, or petrochemical based ingredients.

Limewashes are used both internally and externally. When used externally, casein or tallow is added to improve the ?water-shedding? properties. Casein, a natural glue derived from milk, improves adhesion and Casein Limewash is also used internally on less porous hydraulic lime plasters and masonry. It is also less likely to rub off than Pure Limewash. Limewashes can only be applied to previously painted surfaces if the existing paint is limewash. They should not be applied to previously distemper or emulsion painted surfaces.

Distempers are matt finish water-based paints for internal use only. Three types are available ? Soft Distemper, Casein Distemper, and Oil-bound Distemper. Soft Distemper is the most permeable of the three and normally used on ceilings and moulded plasterwork. It is used on walls, but generally in ?low-usage? areas, as it can be washed off with a wet sponge. Casein Distemper and Oil-bound Distemper are normally used on walls as they are more hard-wearing and more difficult to wash off. Oil-bound Distemper, the least permeable of the three, should not be applied to new lime plaster as there is a potential reaction between the linseed oil and uncarbonated alkali lime. Oil-bound Distemper is the least uniform with the most tonal variation.

Distempers are normally applied to porous building surfaces but will also adhere to modern gypsum plaster and previously emulsion painted surfaces.

Limewash, due to the thin consistency, can be ?messy? to apply and protections must be provided. Face and eye protection and overalls must be worn and applying limewash to ceilings is particularly hazardous and for this reason a distemper is often chosen for the decoration of ceilings. Indeed, many choose to use distemper in preference to limewash for the internal decoration of walls and ceilings.

yup. Makes cheap, long lasting & easy to use masonry paint. It's porous so doesn't block evaporation. Only downsides are it's nasty on eyes, don't put one in the other, and being alkaline is not compatible with all pigments.

NT

There are a lot of lime based paint formulae/types. I wouldn't recommend those personally. Both are bonded by water soluble glue, not ideal for a damp surface.

NT