Waterproof Blue liquid damp proof membrane for treating rising and penetrating damp

Rising Damp vs Penetrating Damp vs Condensation: How to Tell the Difference

“Damp” isn’t one problem — it’s three, and the fix depends entirely on which one you’ve got. Treat the wrong type and you’ll waste money while the damp comes straight back.

Here’s how to tell rising damp, penetrating damp and condensation apart.

Rising damp

Moisture is drawn up from the ground through the wall by capillary action. The giveaway is a tide mark up to around a metre up the wall, often with peeling paper, salts and decaying skirting. It’s caused by a missing or failed damp proof course — and the fix is a barrier at the base of the wall. A liquid damp proof membrane stops ground moisture tracking upward.

Waterproof Blue liquid damp proof membrane Poseidon liquid waterproofing membrane

Penetrating damp

Water moves sideways through the wall from outside — driven rain soaking porous brick, cracked render, or failed pointing and gutters. It shows as localised patches that grow after heavy rain, anywhere on the wall. The answer is to make the outside face raintight but breathable with a weatherproof breathable brick sealer, plus internal protection where needed via The GOAT or Poseidon.

Condensation

Warm, moist indoor air hits a cold wall and turns to water — high on walls, in corners and on windows, usually with black mould. It’s about ventilation, cold spots and vapour control, not water coming through the wall. See our guide to condensation on walls.

Quick comparison

  • Rising damp — from the ground up; tide mark low on the wall.
  • Penetrating damp — from outside in; patches that grow after rain.
  • Condensation — from indoor air; mould high on cold walls and windows.

For the full overview, read what causes damp walls.

Not sure which you’re dealing with? Contact us — tell us the symptoms and we’ll point you to the right solution.

Back to blog