What DIY pressure washing does to render
A hired pressure washer will clean almost anything. It will also strip paint, scar timber and force water behind your walls. Where the line sits.
The assumption we're testing
“DIY-with-a-hired-machine”
The machine isn't the skill
Hire gear is powerful. That is the problem. The skill is not making pressure. It is knowing how little to use, at what angle, with which tip, on which surface.
Most of the damage we get called out to fix came from a narrow tip held too close, on a surface that needed a gentle wash instead.
Surfaces that punish high pressure
Painted and rendered walls mark for good, and you only see it once they dry. Soft timber decking lifts and goes furry, so it needs sanding before it can be sealed again. The mortar between pavers washes out and the whole lot starts to shift.
Roof tiles are the costly one. Too much pressure on old terracotta strips the surface and pushes water up under the tiles. The roof looks great, then starts leaking a month later.
Soft washing is usually the right answer
Most outside cleaning problems are living things, not dirt. Mould, lichen and algae die off with the right treatment and a bit of time. Force does not help.
Soft washing puts the treatment on at low pressure, lets it work, then rinses off. It is slower and less dramatic to watch. It also does not wreck the surface.
This is The Pressure Wash Brigade territory.
See the brigade