Your roof. Specifically, concrete roof tiles — which is what most Penang landed homes have overhead. A pressure lance turns a dirty but healthy roof into a clean, damaged one in a single afternoon, and the damage is the kind you pay for twice: once in the tile itself, and again in what the water does on its way through. It is the most common request we decline to do the fast way.
What high pressure does to a concrete tile
A concrete tile leaves the factory with a thin cement-and-pigment skin that seals the porous concrete underneath. A high-pressure jet strips that skin along with the dirt. The colour goes patchy, but the real cost is that the exposed concrete now drinks water, dries slowly, and gives moss and algae a far better grip than the sealed surface ever did. A blasted roof turns green again faster than it ever used to — which tends to get answered with more blasting.
The water you cannot see
Tile roofs keep rain out by overlap: water falling downward runs from tile to tile and off the edge. A pressure jet is not falling rain — it is a horizontal blade of water at pressures no roof was designed to meet, and swept across a roof it drives water up and under the laps, into the battens, insulation and ceiling boards. You find out weeks later, as a brown stain on a bedroom ceiling that nobody connects to the wash.
Why Penang roofs turn black anyway
The dark streaks on roofs here are not dirt — they are algae, and the furry patches are lichen and moss, all of which thrive on humidity and a rough surface. Penang supplies the humidity year-round. Because it is growth rather than grime, killing it is what matters; blasting it off while leaving it alive at the roots just schedules the regrowth.
Soft washing, the method that works
Soft washing puts a cleaning solution on the roof at little more than garden-hose pressure, lets it kill the algae and lichen chemically, then rinses gently. Dead growth loses its grip and weathers off with the next rains. The tile surface keeps its skin, nothing is forced under the laps, and because the growth is dead rather than trimmed, the roof stays clean for years instead of months.
Where pressure washing still belongs
On surfaces that are solid, sealed or sacrificial: concrete driveways, stone paths, brick boundary walls, porches and drains. That is most of the exterior work we do, and pressure washing starts from RM250. The skill is not owning the machine — it is knowing which surface takes pressure and which takes chemistry. When we quote a house wash, we walk the property and split it into exactly those two lists before naming a figure.
Want it done properly instead?
Window cleaning in Penang starts from RM100, with purified water on every job and both guarantees included.