Should We Use Brick Creams? – Can I Just Ask? – Ep.12

Brick creams — siloxane-based water repellent treatments applied to masonry surfaces — are a genuinely useful tool in retrofit, though one that attracts more debate than it perhaps deserves. The controversy is largely historical: earlier formulations tended to block pores entirely, trapping moisture within the wall and causing problems. Modern brick creams work differently, lining the pores rather than blocking them, so they repel liquid water while still allowing the wall to dry through vapour diffusion. Applied by brush, roller, or spray, the treatment soaks into the top five to ten millimetres of the masonry surface and leaves no visible coating — the wall looks exactly the same afterwards.

In the context of internal wall insulation specifically, brick cream is a useful risk management tool. Adding insulation to the inside of a wall reduces heat flow into the fabric, which makes moisture conditions within the wall more demanding than they were before. Reducing the amount of water the wall absorbs from wind-driven rain in the first place directly lowers that risk, and a water repellent facade treatment is one of the more straightforward ways to achieve that.

There are two important caveats to be aware of before specifying one. The first is longevity: the coating will degrade over time, so if the specification depends on it being in place, the occupant needs to understand there’s a maintenance cycle involved. The second is that the process is effectively irreversible — removing a siloxane treatment from masonry is extremely difficult, so it’s a decision that needs to be made with some care. There are also practical application considerations: a hydrophobic coating increases runoff, which can direct more water onto adjacent untreated surfaces, and because the coating is invisible it’s easy to miss sections during application. Continuity of coverage across the whole elevation matters — treating a chimney stack but leaving untreated wall below it simply redirects more water onto an absorbent surface that’s already doing more work.