Water Staining on Brick and Mortar

Read the pattern before cleaning

A vertical streak below a window sill means water is running off the sill rather than dripping clear. A dark band near grade means splash-back. A wide stain below a gutter joint means the gutter leaks there. Patchy darkness on one elevation usually means that wall simply stays wet longest. Each has a different fix and only one of them is cleaning.

Mortar is softer than the brick

Mortar joints are more porous and considerably softer than the brick faces around them. Pressure washing brickwork erodes the joints preferentially, and once mortar is eroded the wall takes on more water, which makes future staining worse. On older lime mortar the damage happens fast.

Organic growth versus mineral

Green and black on brick is usually organic and responds to soft washing. White bloom is efflorescence, which comes from inside the wall. Orange is iron, either in the brick itself or from a metal component above. Treating all three the same way is how people get poor results and damaged mortar.

Fix the water, then clean

Cleaning a stain fed by an active water path buys one season. Extending a downspout, correcting a sill drip edge, or repairing a gutter joint changes the outcome permanently, and it is usually cheaper than repeated cleaning.