Sealing a stone wall?

[Gaspode]

I have an old cowshed, which is currently used for storing stuff. I'd like to use it a bit more as a workshop, so I'd like to smarten it up inside a bit. The back wall of this shed is pretty rough stone, and it's pretty scabby, with lots of mildewy/salty/dampy stuff on the surface which seems to keep appearing.

I was thinking of giving it a good hard brushing with a stiff-bristled brush and then spraying it with something like Thompson's Water Shield. The wall is something like 30 feet long and 15 feet high, so it's a fair sized area.

Is this a stupid plan? Is there something better I could/should do (at a reasonable cost)?

[Sam_68]

Make sure its properly pointed before you start, and if you're Cotswolds (I see your profile lists your location as Gloucestershire) then it should be pointed using lime mortar (not cement mortar) and preferably with a 'buttered' mortar joint rather than any sort of raked or recessed joint, as the local limestone needs all the help it can get in the weatherproofing department.

It's not widely appreciated these days, but traditionally a lot of Cotswold stone houses were limewashed for weather resistance, so this would be the way to go for authenticity, but it's not cheap these days. And it needs doing regularly , or it simply washes away... which is the reason it's fallen out of fashion.

The 'Thompsons Water Seal' type products will help a bit if you want a cheap, temporary measure but they seal the surface of the stone and so restrict the way it 'breathes'; they might cause more harm than good in the long term.

[Gaspode]

Thanks Sam. Yes, it is Cotswold stone, and has been pointed with lime mortar, which is in reasonable nick - certainly not worth hooking out and re-doing. I am starting to think that a better (although much more expensive) idea might be to batten and line the wall with something up to a height of 6 feet or so, leaving a decent air gap back to the wall?

[Toilet Duck]

Gaspode said:

The back wall of this shed is pretty rough stone, and it's pretty scabby, with lots of mildewy/salty/dampy stuff on the surface which seems to keep appearing.

How on earth do you know its "salty" unless you licked it?

[Spudler]

Gaspode said:

I am starting to think that a better (although much more expensive) idea might be to batten and line the wall with something up to a height of 6 feet or so, leaving a decent air gap back to the wall?

This is the better option.
Never a good idea to "seal" stonework.

[C Lee Farquar]

Sealing is unlikely to work if there is heavy salt contamination. Years of nitrate contamination wont have helped. Paneling would be best.

[TooLateForAName]

Sam_68 said:

It's not widely appreciated these days, but traditionally a lot of Cotswold stone houses were limewashed for weather resistance, so this would be the way to go for authenticity, but it's not cheap these days. And it needs doing regularly , or it simply washes away... which is the reason it's fallen out of fashion.

Make your own limewash - costs pence.

take a plastic dustbin, place sack of lime inside. Use a mask/goggles/gloves and slash the bottom of the bag before filling dustbin with water. Remove the bag leaving lime in the bin. Stir a bit with a stick and leave for a couple of weeks (some people advocate 6 months, but for limewash you could manage a very short wait).

The lime will form into a putty like mass. The longer you leave it the harder the putty gets (but it won't set if you keep it under water).

When you make up the limewash, wet the wall down first and then make the first coat very dilute - you could just take some of the water from the bin. stir up the lime with some water to make limewash. several coats and let them dry. It goes on pretty much transparent and only turns white as it dries.

Make sure you use eye protection - lime isn't the most pleasant stuff to get in your eyes.

My last sack of lime was £4.50

[Gaspode]

Toilet Duck said:

How on earth do you know its "salty" unless you licked it?

There are patches of a kind of crystalline efflorescence on the surface of the stone in places. The shed is a lean-to, and this wall is the end wall of a neighbour's house.

But thanks guys, I suspected that sealing might not be a brilliant idea, which is why I asked.

[Wings]

Gaspode said:

There are patches of a kind of crystalline efflorescence on the surface of the stone in places. The shed is a lean-to, and this wall is the end wall of a neighbour's house.

But thanks guys, I suspected that sealing might not be a brilliant idea, which is why I asked.

It could be efflorescence salts, that would be best dealt with by washing down with Acetic Acid, which is vinegar, and white/clear vinegar can be purchased in 5 ltrs. containers from some grocer supermarkets.

[ColinM50]

I'd go with the battening and insulated plasterboard. Since it's a shed maybe no need to go too mad but Sheffield Insulation are very good. Don;t be put off by the name they've got depots all over the UK

www.sheffins.co.uk

[ColinM50]

Gaspode said:

The shed is a lean-to, and this wall is the end wall of a neighbour's house.

Out of interst, does the neighbour have the same damp problem on his side of the wall? If so then maybe he needs to do something about curing the problem rather than hiding the symptons.

[Gaspode]

ColinM50 said:

Gaspode said:

The shed is a lean-to, and this wall is the end wall of a neighbour's house.

Out of interst, does the neighbour have the same damp problem on his side of the wall? If so then maybe he needs to do something about curing the problem rather than hiding the symptons.

No, it doesn't seem to. The building was an old set of stables which was converted to a house about 15 years ago. I'm not certain, but I think they may have tanked the wall on their side prior to plastering it.

[Wings]

ColinM50 said:

I'd go with the battening and insulated plasterboard. Since it's a shed maybe no need to go too mad but Sheffield Insulation are very good. Don;t be put off by the name they've got depots all over the UK

www.sheffins.co.uk

In one rental property I own, damp course treatment was carried out by covering the wall with a bubble wrapped polythene, then fixing battening against wall, with plasterboard on top and skimming over with plaster. Perhaps if you are using the space/wall for garage, tools etc., then perhaps instead of plasterboard use either marine ply or MDF board.

[Gaspode]

Wings said:

Perhaps if you are using the space/wall for garage, tools etc., then perhaps instead of plasterboard use either marine ply or MDF board.

Yes, I was thinking of using marine ply, on the basis it would be reasonably damp proof, and I could paint it with a nice light background.