Is my damp condensation?

numptydumpty18

Before I shell out for a damp survey I thought I'd get some opinions.

1930s bungalow with cavity walls (no insulation). We get some mould and peeling paint at a low level on one external wall in a bedroom, just above skirting. Moisture/conductivity meter readings on wall are very high, say 50% at bottom of wall (appreciate the moisture meter readings are very subjective). If I scrape off paint and lining paper to get to plaster, reading is about 20%, which is about what I get on other dry walls in the house. So, as the moisture seems to be limited to a couple of mm of the wall surface is it more than likely condensation?

If so does insulated lining paper work well to eliminate condensation?

stuart45

There's a good chance that's condensation. Have you got any air bricks that ventilate the cavity. If so, these can cause cold spots on the wall.
Mould is often found where there's condensation. With rising damp the salts stop it living there.

numptydumpty18

@stuart45 Good question, there was an air brick that ventilated in that area (not sure if it was the cavity or floor void). It was previously blocked off, I recently unblocked it to see if it helped and it looked like it made the moisture readings worse, I'm assuming as it made the wall colder. I have just temporarily blocked it again to see the effect.

stuart45

It probably would make the wall colder to have it open. Air bricks were used to ventilate cavities back then, but they were found to cause cold spots on the internal walls, and increase the U value of the wall to greater than a solid 9inch wall.

FreeBear

Quite possible that there is no sleeve between the external & internal air bricks. So if the air brick was blocked up outside, the cavity gets colder once the blockage is removed.

Some people have had a modicum of success reducing condensation with products like Wallrock thermal lining paper. For ~£25 per roll, it might be worth a try (I'm skeptical about the claims made by the manufacturer, but it does work for some). Longer term, it is worth considering internal wall insulation (say 50-75mm of Celotex) - That would dramatically reduce the heat loss through the wall and make the room much easier to heat. In doing so, stop condensation & mould, and reduce the heating bill.

stuart45

It's worth checking whether the air brick is for cavity or underfloor ventilation.
If it's the latter, it needs to be left open.