On Nov 2, 9:26*pm, wrote:
Hello.

I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?

My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.

Thank you.

Ed.

If your walls are cavity, the only way damp can penetrate is if the
cavity is bridged in some way (rubble/cement droppings etc.) ie some
constructional defect
Condensation is more likely.

Determining the source/cause of damp needs experience.
More info/pix needed.

If you tap on rendering and it sounds hollow it is an indication that
it has become detached/"unstuck" from the wall. However this in itself
should not cause damp to penetrate a cavity wall.
At some point it will fall off/get much worse & have to be fixed.
Probably caused by frost action.