What is the white powder on my brickwork?

Almost certainly efflorescence — mineral salts carried to the surface by water and left behind when it evaporates. It looks alarming and is usually harmless in itself, but it is telling you something.

The mechanism. Bricks, mortar, concrete and render contain soluble salts. When water moves through the material, it dissolves them. When that water reaches the surface and evaporates, the salts are deposited as a white crystalline bloom.

So efflorescence is not a defect in the surface — it is evidence that water is moving through the wall.

When it is normal. New brickwork very commonly effloresces during the first year or two as construction moisture dries out. This is expected, diminishes over successive drying cycles, and generally needs no action.

When it indicates a problem. Efflorescence appearing on established brickwork, or recurring persistently, means water is getting in. Worth investigating:

Failed or missing damp proof course, or ground level raised above it.

Leaking gutters, downpipes or a cracked hopper saturating one area — often visible as a vertical band.

Defective pointing letting water into the joints.

A bridged cavity, from mortar droppings or debris.

Plumbing leaks internally.

Missing or damaged coping and sills allowing water into the top of a wall.

How to remove it. Brush off dry with a stiff bristle brush — not wire, which damages brick faces and leaves iron deposits that rust. Do not wash it off with water, which dissolves the salts back into the wall to reappear later. Repeat over several dry spells; it reduces as available salts deplete.

Acid-based cleaners exist but can damage mortar and are best left to professionals.

A related and more serious problem is crypto-efflorescence, where salts crystallise beneath the surface rather than on it. The expansion spalls the brick face off. That is genuine damage and needs the water source addressed urgently.