Hello,
I've moved into a 1950's house with externally rough casted walls. I had planned to repaint the exterior walls in the summer but this week, after some heavy rain, I have discovered two small damp patches on the interior plastered walls about the size of your hand. On closer inspection to the exterior walls it seems there are a few hairline cracks which I would imagine are the cause of the damp patches. Could anyone please advise a product or course of action which would seal the cracks against anymore of the winter weather until I can get painting once we get some better weather?
Many thanks.

A good silicone sealant (exterior grade) would do the trick I'd imagine!