How to Prep a Building Exterior Before Repainting

Yes, and it is the most important step. Exterior walls carry chalk from the old coating breaking down, plus mould, dust and salts. Fresh paint bonds to that loose layer rather than the wall itself, so it peels within a year or two. A proper soft wash removes all of it and gives the new paint a clean, sound surface to grip. Skipping the wash is the single most common reason a repaint fails early.

Chalking is the fine powdery residue that forms as an old exterior coating slowly breaks down in the sun. Rub your hand on a faded wall and the powder that comes off is chalk. If you paint straight over it, the new coat sticks to that loose powder instead of the solid surface underneath, so it lifts and flakes. A soft wash strips the chalk back so the fresh paint can key into the wall properly.

Soft washing is the right choice for most painted exteriors. High pressure can gouge render, blast paint off in uneven patches and force water deep into the wall, which then has to dry before painting. Soft washing uses low pressure and a cleaning solution that kills mould and lifts chalk and grime without damaging the surface. Our guide on soft washing versus pressure washing in Sydney explains when each method suits the job.

Give the walls a few days to dry right through before the painters start. Painting over a damp wall traps moisture and causes blistering and peeling later. On a dry Sydney week the surface usually dries in a couple of days, though dense render and shaded walls take longer. Check the forecast and coordinate the two jobs so there is no rain in the gap between the wash and the first coat.

A soft wash kills mould and algae at the root rather than just wiping the surface, which is why it lasts. If mould is only painted over, it keeps growing and bleeds back through the new coat as dark patches. Treating it properly before painting stops that happening. On shaded, damp walls it is worth being thorough, since those are the spots where mould returns fastest if the prep is rushed.

Yes. The same principles apply on larger buildings, just with the right access equipment and low pressure at height. Office fronts, strata blocks and industrial units collect a film of traffic pollution and grime that blocks paint adhesion and dulls the finish. Our commercial exterior cleaning team preps these buildings before a repaint and works around tenants and trading hours to keep disruption low.

It can. Painters often price in extra prep time when they see a dirty, mouldy wall, because they know they will have to clean and scrape more before they can start. Handing them a clean, dry surface removes that unknown and can sharpen their quote. It also means their labour goes into painting rather than cleaning, so you get more coats and better coverage for the same job.

Send us photos of the walls and your address through our free quote form and we will come back the same day. Pricing is job by job because the surface type, size, how much chalk and mould there is and the access all change the time on site. We lock in the exact price before we start, and we can time the wash to line up with when your painters are due to begin.