Pressure Washing Before Painting: How Is It Done?

Pressure washing removes dirt, algae, dust and loose paint so that the new paint bonds well. Without it, the paint can peel within a few months, because it sticks to the dirt and not to the wall. It is done with clean water at controlled pressure, and you need to let the wall dry before painting.

Why this step matters

Paint only lasts if it is firmly attached to the surface. An exterior façade has dust, traffic soot, grease, mould and algae. If you paint over them, the paint forms a film on top of that layer. When the layer comes away, it takes the paint with it.

In damp or shady areas, such as north-facing walls or walls next to trees, algae and mould come back quickly. If they are not eliminated, they will show up again underneath or through the new paint.

How it is done, step by step

  1. Protect anything that is not being painted: windows, doors, light fittings, sockets and plants.
  2. Close windows and doors properly so water does not get into the house.
  3. Start with low pressure and increase it only if needed.
  4. Wash from top to bottom, in even passes, keeping a constant distance from the wall.
  5. On areas with algae or mould, use a suitable product to kill these organisms and leave it to work for the time the manufacturer states.
  6. Rinse well so that no product residue is left behind.
  7. Let the wall dry completely before any repair or painting.

Taking care not to damage the wall

Too much pressure causes damage. It can make holes in weak render, strip the material out of the joints and push water into the walls. It can also leave marks and streaks on the surface. So always do a test in a discreet corner before washing everything.

And after the wash?

Washing shows the true condition of the wall. This is when cracks, hollow areas and loose render appear. These areas should be repaired before painting. Painting over loose render is throwing money away.

Drying time depends on the season and the exposure. On a dry, sunny day, the wall dries faster. In winter, or on walls in the shade, it can take considerably longer. Do not paint while the wall is damp. If in doubt, wait another day.

If the house has very old, flaking paint, washing alone may not be enough. You may need to scrape or sand the loose areas by hand before applying the primer.

Safety

Washing high areas with a pressure washer from a ladder is dangerous, because the jet pushes you backwards. For tall façades, hire professionals who work with scaffolding or a platform and have the right equipment.

Tip: Schedule the wash a few days before painting, with a dry forecast. That way the wall has time to dry and you do not lose days waiting.

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