Hopefully if all goes to plan my workshop/man cave should be getting a new roof next month.

Currently it’s bare sandstone internally, which is very crumbly. What’s the best stabiliser to apply before painting the walls white?

Also need to mouse proof it, I was just going get a small box of cement and fill in any suspicious holes, does that sound along the right lines?

Thanks in advance.

Sbr might do it
I just sell it, not a stonemason.

If it’s crumbly you need to brush it all off, sandstone breaths so you shouldn’t seal it, stops it drying naturally when it absorbs water, the traditional ‘paint’ is lime wash, this breaths, and lime mortar to fill holes, cement eats sandstone when it comes into contact with moisture.

If you are not insulating the walls why not clean it up and have just that?

Thanks for the info.

I’m trying to make it a brighter place to be. And not have grit/sand everywhere.

So would it need stabilizing before a lime wash was applied?

Ty Mawr Lime in Wales are very helpful, this video by them shows the Limewash Process.

So would it need stabilizing before a lime wash was applied?

Not sure what this means? in what way is it unstable? you will need to get it fairly dust free before a lime wash or it will be all gritty and lumpy, does it need pointed? gaps between the blocks?

I mean with a paint on agent such as that SBR. But then I guess not as lime wash is direct onto the stone.

If its crumbly, its because its damp and can’t breathe.

Our house has 2 external faces clad in gritstone setts (so coarse sandstone). The pointing had been bodged over the years with an assortment of Portland cement mixes, tile grout etc. and some of the blocks were dissolving before our eyes. We had the whole thing repointed with lime mortar and within 10 days the worst affected bits had gone solid again and its been that way ever since.

Basically don’t go near it with normal cement and make sure it can breathe properly.

If its crumbly, its because its damp and can’t breathe

This would be my answer too, a good example is the end of my building, roof was off and the walls were in a bad way, white salt staining and black fungus stains, dark and light bits where the moisture had got in and it was crumbling in places, repointed with lime mortar and you could see it dry out in days, it’s a couple of years now and the walls are completely uniform and as good as the day they were built, they get wet on the outside and dry naturally, all working as it should and did since 1882.

Planning dept forced me to tank 5′ up the walls of one part with a mix of SBR and tanking slurry, those walls are now retaining damp, started within days, I now have to dig a french drain on the outside to compensate and try to fix the damage done, the tanking slurry stops the moisture evaporating naturally and it builds up behind it as a wet patch, this goes soft and crumbles over time then the coating and rotted bit behind it falls off in a big flat layer.

Some walls were white washed with lime at some point in the past, those are fine.

I have another bit outside in a corner protected from rain, this was eroded away, big pile of dust below, although dry and well ventilated on the crumbly side this was drawing damp from the other side, a farmer had piled up earth on the other side of the wall and the sandstone was absorbing it, it crumbled on the ventilated side, hence why walls go crumbly on the often dry inside.

We had the whole thing repointed with lime mortar and within 10 days the worst affected bits had gone solid again and its been that way ever since.

It is strange how quick it restores itself, very satisfying, but you missed out by not doing it yourself, I dreaded it, after an hour(of making a complete pigs ear of it) I was zipping along like a pro and really enjoying it.

The worst of my wall is below the leaky part of roof, so hopefully once the roof is done the wall won’t be as damp.

I’ll give the walls a good brush down and apply some lime wash.