How to Clean Brickwork: Methods, Risks and the Sealing Debate

What spalling is and why high pressure causes it

Spalling is when the face of a brick cracks, flakes or breaks away, usually because moisture has been driven into the brick and then expands, often through a freeze-thaw cycle, forcing the surface to fracture. High-pressure jet washing can directly contribute to this by driving water deep into brick and mortar that wouldn't normally absorb that much moisture that fast, and by eroding the brick's fired outer surface, which is more weather-resistant than the material underneath. Once spalling starts, it tends to accelerate, since each cycle of moisture ingress and freezing widens existing weak points further.

Older handmade or soft-fired bricks, common in Victorian and Edwardian properties across the North East, are particularly vulnerable, since they were never designed to withstand modern pressure washing equipment, having been made for a world without domestic jet washers at all.

DOFF steam vs traditional low-pressure methods

DOFF cleaning uses superheated steam at very low pressure, roughly the force of a garden hose, to lift dirt, algae and old coatings without saturating the brick with water the way pressure washing does. It's become a preferred method for heritage and soft brick work because it cleans effectively while minimising moisture penetration, and is often specified on listed or conservation-area properties for exactly this reason.

Traditional low-pressure washing combined with a biocide pre-treatment is also effective and more widely available, generally a good choice for modern, harder-fired brick in reasonable condition. The right choice between the two often comes down to the brick's age, condition and porosity, which is worth a professional assessment before committing either way.

The sealing debate

Sealing brickwork after cleaning divides opinion in the trade. Advocates argue it repels water and slows algae regrowth, extending time between cleans. Others point out that breathable brick relies on being able to let moisture pass through and evaporate, and the wrong sealant can trap moisture inside the wall, causing damp problems that are worse than the algae it was meant to prevent. This is a genuine trade-off worth discussing properly rather than a decision made on the day of a clean.

The honest position: on modern, well-fired brick with a genuinely breathable, vapour-permeable sealant, it can be a reasonable choice. On older, softer, or already damp-prone brickwork, sealing is generally not recommended without a proper assessment, since trapping moisture in old solid-wall construction can cause real problems.

Costs and getting an assessment

Professional brick cleaning, whether steam or low-pressure with biocide, typically costs around £15-£25 per square metre depending on method and brick condition. Given the real risk of spalling and long-term damp issues from getting this wrong, brickwork cleaning is one of the clearer cases where a professional assessment before starting is worth the conversation, particularly on period properties.