Can someone explain breathable paints please?

[sleeplessbunny]

We are in a stone cottage which has been rendered and painted with some kind of waterproof plastic-y masonry paint. After the horrendously wet weather we had earlier in the winter, we started getting damp walls inside the house. I scraped a bit of paint off the outside of the house in a particularly bad area and water just kind of gushed out from underneath the paint.

I scraped off as much paint as I could to try and let the walls dry out, and it seems much better now, especially since the weather has been much drier.

I understand that old houses need to breathe, and obviously sticking a layer of plasticy paint all over it was a bad idea (previous owner!), but it's got me thinking about breatheable paints. I tried googling but was met with a tonne of marketing material that didn't make a lot of sense, and some of these paints are VERY expensive. I need to do some repainting inside the house as well, but I want to make sure I use the right stuff.

So can anyone give me the dummies guide? Emulsion, vinyl, acrylic, mineral, silicate, limewash, all these words are just swimming about in front of my eyes without actually telling me anything

[BoBoo]

Is this any use?

[specialsubject]

not sure I'm that expert, but we used Naturepaint for a similar situation - the walls were going mouldy beneath the hideous vinyl wallpaper when we moved in.

it's quite an effort as you need to mix it up, but with a special 2-for-1 it wasn't that much more than standard paint, and it certainly is nice not to have the smell. You also wash brushes in a bucket and then tip the used water on the compost heap or into a corner of the garden!

it doesn't go on as well as standard paint (it is a technological step backwards) but it works in the end.

does it work? one wall is now fine. Another is still damp (we haven't totally solved the background problem) but once we've taken other measures we'll put on another coat. It doesn't help that the outside of the wall is covered in modern non-breathing paint, old walls need to breathe.

[PigletJohn]

Water getting behind paint or render and actually running out has more often got in through a crack or hole from rainwater especially by a leaking gutter or downpipe. Look for that first because if any, it will be causing bad wet regardless of paint.

How old is your house and what are the walls covered with? Lime, cement, gypsum plaster?

[sleeplessbunny]

Yes piglet i'm sure there is a bigger problem that needs fixing first, the guttering is under investigation. I admit the paint question is a secondary issue, but it is bugging me all the same.
The house is probably about 150-200 yrs old and I have no idea what the render is, probably cement I suppose (groan)

[PigletJohn]

Try to find out what the local practice is in your area. Other people with similar homes will have been through it before.

I have never had a stone home and round here are only a few flint and lime ones.

If your home has lime render it will tend to have rounded corners and be soft enough to scratch with a spoon.

Render is supposed to be weaker than the substrstrate.

Render is usually applied to hide a defective wall.

[PigletJohn]

substrate

[Sausagedog27]

If it is cement render then it's pointless putting on a breathable paint- you will need to rerender in lime to help with the damp. Good luck!

[wonkylegs]

If it's a cement based render then there is no point in breathable paints on the outside as it's not a breathable layer that you are painting. Cement renders are very hard, most modern renders will be cementitious. If it's a very old crumbly almost soft render it's more likely to be lime based and breathable paints are worth considering. I can't recommend any external ones as I've never used any, sorry.
Render isn't just used for covering up defective walls but is both traditionally and modernly used to make a cheap construction look more expensive. Regency houses are a good example of this, but it's also used throughout history for this purpose.
Agree if there is a 'gush of water' then there is an underlying problem that needs to be fixed (guttering is a likely cause) and dried out before you can contemplate doing anything else. Fixing the problem is most likely the solution to sorting the damp rather than paint issues.

[PaulPearson]

I know that this is a very old post! but i came across it whilst looking for something and just wanted to share my expertise.

From the sounds of your post, the paint was applied to try and waterproof the cottage, possibly to deal with a previous damp issue or maybe due to lack of knowledge about how older buildings work.

Older buildings need to be able to breath, the reason many of them feature such thick walls is because thats how they protected against water penetration, when it rained the wall would get wet, when it stopped raining the wall would then dry out. Providing it didn't rain too much for a long period of time then the walls would usually dry out eventually.

By painting the wall they stopped the rain getting in, but most importantly they also stopped the water getting out, so when you had the heavy rains it broke through the seal (probably at the top where water over ran the guttering and soaked through the top of the wall)

Once in the wall the water had no where to go and started damaging the inside of the wall, hence the damp inside the house.

You said that when you removed the paint the wall literally gushed water.

So the answer really is to get the exterior of your walls power hosed or sandblasted to removed the rest of the paint and then to apply a finish that will protect the wall but also allow it to breath.

I can recommend a company called Keim Paint, who produce a number of specialist renders, paints that would allow your house to breath properly. Alternatively use something like a lime wash or lime based paint to your cottage.

Any sort of cement based render will make the situation worse as will any emulsion paints.

If your still having problems then contact a local renovations company or architect who will be able to help.

[Londonfather]

We previously had a damp problem, but this is ok now. The outside of our house is pebble dashed and since painted. We have ad rust lines coming down the paint from iron in the pebble dash. We have chipped out some of the rust and filled the gaps with sand and cement but it's impossible to remove all the stones which might have iron in them as the pebble dash is all over the house.
We want to paint the house again with some paint which will reduce the risk of rust formation but at the same time not increase the risk of damp. We were thinking of pliolite? Any tips guys?
Thanks