Hi

The house is 1930s single wall construction. The exterior is pebble dash painted white over what I believe to be a lime based render. I don't know if it's lime render or cement render with lime. It looks chalky (if I lift the paint) and fizzes If in contact with vinegar.

We have some damp patches appearing on the inside wall after heavy rain. Trying to identify the source of the water.
The render feels badly blown in some areas, but upon inspection it's clear that only the paint layer is blown. The render behind the paint is damp but otherwise sound. The paint is not obviously cracked.

What's a more likely explanation for the source of the damp?
Could the old blown paint have become porous and let water in?
或者有可能基于石灰的渲染是absorbing loads of moisture and transporting it up to 2 metres away? If this type of render is so absorbent then the culprit could be some poor guttering/flashing, but this is 1.5 metres away from the latest damp patch.

Thank you!