We recently moved into a 1930's bungalow (double thickness brick wall with no cavity then lath and plaster). When removing wallpaper from front bay window room I noted dampness. When I pulled off the plaster, there was a lot of trapped material blocking the space between the brick wall and the plaster, like damp sand, plus some solid damp material which I assume was the old plaster that fell down the space during the original lath and plastering. where this stuff was lying against the joist it has caused crumbling. Where the joist ends slot into the wall, the same damp sandy dust has again caused dampness and crumbling of the joist ends.
Now I have some ideas as to the cause of the dampness. As you will see from the photos, the dpc seems quite low (two bricks below the air brick). There has been a monoblock driveway put in previously and you can see that the top of the block is about 2 inches above the DPC. In addition, there is some pooling of water where the block meets the front wall after it rains. There is also a drain that runs from the front corner of the house (where the dampness seems to be the worst) and the drainage hole at the end of the trench was been completely blocked. I think this may the problem which has been causing the dampness. I've now unblocked the drain. Would be keen for your thoughts.