We are rennovating our bathroom in a 1900 terraced groundfloor flat. The whole road is purpose built workers homes with each flat having its own front door and garden. Out back they used to have a loo room that looks like it was an add on although all the flats seem to have one. We are putting a loo back in the loo room and have discovered that the 2 external walls, one with a drain outside it is worse than the other, have some damp at ground level up to about 3 bricks. There are no tide marks or obvious salty deposits on the wall, we've stripped back the plaster to the brick and some pointing mortar is crumbling away so we've removed that and plan to repoint with a lime based mortar. But we're after some guidance on the cause of the damp, which we think is rain penetration as it got a lot worse after heavy rain and appears to dry out when we have dry spells. Are we on the right path? Thanks!