The Great Rising Damp Debate

[Anonymous]

We had test-tubes, with coloured water in the bottom, that we filled with either salt or sugar. Great fun, watching the capillary action. No-one asked (and no-one told us) about how far the water would creep, given a long enough tube.

 

[Anonymous]

For a glass tube height in cms is about 0.3 divided by diameter of tube in cms.

Bricks, of course are not the same as glass tubes. That's the trouble with school science. Nevertheless the pore size in brick and stone is of the sort of size that should allow capillary movement of water several feet up a wall. But I think there may be other important factors involved in damp rising or not:
1. The supply of water to the bottom of the wall. This depends on the wetmess of the soil outside and wheter there is a DPC in the floor preventing drying out over a large area.
2. The rate at which water can move through the wall. Small pores allow higher capillary rise but the rate of flow is less than if the pores are larger.
3. Evaporation out from wall sides. If evaporation is faster than capillary rise the water will not get very far. But if evaporation is slower than capillary rise the wall will get damp.

 

[Anonymous]

"... the wet mess of the soil outside..."??

You've spotted my garden, haven't you?!