Damp Solum/Sub-floor

[danensis]

The big problem with dampproofing contractors is that they are basically selling snake-oil. You do get dampness in buildings, but it is usually caused by lack of ventilation, soil heaped against walls, leaking gutters or leaking pipework (both downpipes and weeping water pipes). The only way to tell if a wall is damp is to take a core sample, weigh it, dry it, and then weigh it again. So called "damp meters" are totally useless, as they are designed for timber, not masonry, and are affected by so many variables you cannot take them all into account.

For the sceptical, I always recommend the following experiment: Take a bowl of clean water, and stand four bricks on top of each other in the bowl, and see how far up the bricks the line of damp appears. I have yet to see the second brick get wet. But, people say, what about capillary action? Well capillary action does exist, but in closed tubes, and there are few of them in bricks. Any water absorbed by the one damp surface of the brick will evaporate from the two exposed surfaces, as long as there is sufficient ventilation.