This was the old house when we took it on:
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It looks reasonably tidy, but it was not. It clearly had a major damp issue throughout and needed sorting out.
I think from day one, or maybe in it's early years (maybe something had triggered it) it had been a problem house. It is built from sandstone and millstone grit on the most exposed facades which are solid and 500mm thick, the others are from shale. We get days of continuous rain with howling winds in Winter. The wind drives the rain into the porous stone until it comes through. You can see very poor extensions with roof pitches which are too low. Water gets into the original stone house wall and runs down behind the flashings of the extension roofs and comes in. It drives through upstairs too.
The first move (decades ago) was to repoint the house in OPC, this is Ordinary Portland cement and was a very bad move. Houses like this were built using lime mortar which breathes, OPC does not so it made the problem worse. You see, water can get in, but now it can't get out very easily because the cement mortar is holding it back. You can see it here:
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Some bright spark came up with the idea of coating the whole gable end in black bitumen. This made it even worse again. If you've ever grafted and sweated with waterproof clothes on then you'll know about damp build up on your body, this is very much the same. The water can not get out and be evaporated by the sun and wind so it just sweats.
That didn't work, so the next move was even better. Someone mixed OPC with water into a thick paste and painted the whole house in it

Then it was coated in numerous coats of plastic masonry paint. At this point if the house could scream I think it would have.
You absolutely cannot stop water from entering a masonry wall, you have to deal with it when it's in there as you will not prevent it.
Then we came along and bought it, warts n all

I have a building trade background so had a good idea of what I was doing, but even so there has been a lot of history to uncover and learn.
Within a few weeks of moving in I got quotes for blasting all of this s**t off the house. They started here:
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Which grew:
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And went on:
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If you look at all the pics you can see how dark and damp the original house walls (not the extension) are. That was in August/September after it had no driving rain for maybe 6 months.
They say solid walls like these dry out at an approximate rate of 1mm per month.
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You can see how the front is drying here, but this gable is still damp. That's why the old sycamore is getting a bit of a prune
After many decades of torture the house at least looked like it should, could now breathe and start to dry out. This was just the first phase of many though. At the moment I'm chiselling off the cement pointing ready to re-do it in lime. Whoever did it at the front and Westerly gable made really strong mix (it's like granite) and put plenty on. It's bonded well to the porous gritty stone and is taking a lot of hammering to get it off.