How to Stop Penetrating Damp in Brickwork

Older and exposed masonry can soak up driving rain, leading to penetrating damp, cold walls, internal staining and frost damage. The challenge is stopping water getting in without trapping moisture inside the wall.

How to spot penetrating damp

Unlike rising damp (which starts low and tide-marks up to about a metre), penetrating damp shows as patches anywhere on the wall — typically on the most weather-exposed elevations, after heavy or wind-driven rain. You may see internal staining, blistering paint, cold spots and, over time, spalling brick and mortar as trapped water freezes and thaws.

Why brickwork gets damp

Brick and mortar are porous by nature. In exposed locations, wind-driven rain is absorbed faster than the wall can dry, raising its moisture content, reducing thermal performance (wet walls lose far more heat) and risking long-term decay. Approved Document C requires walls to resist moisture passing to the inside — and a saturated wall struggles to do that.

Breathable is the key word

The wrong fix is a film-forming, non-breathable sealer that traps moisture in the wall. The right fix repels liquid rain from outside while staying vapour-open, so any moisture in the masonry can still dry out.

The solution: a breathable masonry water repellent

Passivhaus Brickseal is a cream-based water repellent that penetrates deep into masonry and cures within the wall. It repels rain while remaining fully vapour-open, so the wall keeps breathing — and it dries clear, preserving the original appearance, which matters on heritage and visible brickwork.

How it is applied

• Start with clean, dry, sound masonry (repoint any failed mortar first)
• Brush, roller or spray on the cream
• It absorbs and cures invisibly within the wall

Benefits

• Invisible finish — ideal for heritage and visible brickwork
• Breathable — no trapped moisture
• Improves thermal performance by keeping walls dry
• Long-lasting weather protection

Frequently asked questions

Will it change the look of the brick? No — it cures clear and matt.

Is it the same as rising damp treatment? No — rising damp needs a DPC/DPM; see our rising damp guide.

Compare your options in Damp Walls? Two Breathable Solutions, or get advice.