Penetrating damp is rain pushed through a wall or a failed seal from the outside, rather than groundwater rising up from below. In wind-driven Cape winter rain it is common, and spotting it correctly saves you paying for the wrong fix.
Penetrating damp shows as a damp patch that appears or worsens after rain, often part-way up or high on a wall rather than only at skirting height. You may see a localised stain, blistering paint or a darker patch on the inside of an external wall, frequently on the side that faces the prevailing wind and rain. Unlike rising damp, it has no neat tide-mark a metre off the floor and usually no salty crust.
Rising damp climbs from the floor with a tide-mark and salts. Condensation forms on cold surfaces like windows and in poorly ventilated corners, and is paired with black mould rather than a single wet patch. Penetrating damp is tied to rain and to a specific external defect, so it often comes and goes with the weather. Getting this right matters because all three have different fixes.
Common Cape Town causes are cracked or porous external plaster, failed pointing in face-brick, a leaking gutter or downpipe, a failed window or door seal, a defective parapet or balcony, and bridged or missing flashing where a roof meets a wall. The water finds the weak point and tracks through to the inside.
The fix is to find and repair the external defect first, the crack, the seal, the gutter, then seal or re-coat the wall so it sheds water. Sealing the inside without fixing the outside just traps the moisture. A specialist traces the entry point rather than treating the visible stain, which can be some distance from where the water actually gets in.
Rising damp has a tide-mark up to about a metre with salt deposits and is worst at skirting height. Penetrating damp is linked to rain, often appears higher or part-way up the wall, sits on an external wall, and has no salty tide-mark. A moisture meter and a look at the outside wall settle it quickly.
No. The external defect that lets the water in will keep letting it in every time it rains, and the damage spreads to plaster, paint and eventually timber. The sooner the external cause is fixed, the smaller the repair.
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