Cleaning brick and masonry

Brick spans two centuries of manufacturing and the difference matters more than anything else on this page. Modern extruded brick is hard, dense and takes 1,200–2,000 PSI comfortably. Soft-fired historic brick has a fired skin over a soft body, and once that skin goes the brick erodes for the rest of its life.

• Scratch test. A key on an inconspicuous brick. If it powders, treat the wall as soft.
• Look at the mortar. Soft lime mortar means old brick and a low-pressure job.
• Check for previous repairs. Hard cement pointing on soft brick is already a problem; cleaning will show it.
• Test patch, always. Somewhere the customer does not look, and check it dry.

For sound modern brick: 1,200–2,000 PSI through a 25-degree green tip, kept moving, held back far enough that the spray is a fan and not a chisel. Work top down so runoff does not stain what you have already cleaned, and keep the wall wet ahead of the tip.

What pressure will not do is remove mineral deposit, paint or carbon staining. Reaching for more pressure when the wall stops improving is how brick gets ruined. When pressure stops working, the answer is chemistry.

The white powdery bloom on masonry is soluble salt that has migrated out of the brick or mortar with moisture and crystallised at the surface. Washing it off with water partially dissolves it and drives some back in, and it returns within weeks — often worse, because you have added moisture.

Treat it with a proprietary efflorescence remover, and tell the customer the honest part: the bloom is a symptom of water moving through the wall. Until the water path is dealt with — a failed gutter, ground level against the brick, a leaking downpipe — it will keep coming back regardless of how well you clean it.

Masonry cleaners are usually acidic, and the sequence matters more than the product.

1. Pre-wet the wall thoroughly. Dry brick drinks the acid deep into the pores where it cannot be rinsed out and continues working, leaving burns.
2. Apply the weakest dilution that works. Test it. Start weaker than you think.
3. Keep the dwell short and never let it dry on the wall.
4. Rinse thoroughly, from the top, with far more water than feels necessary.
5. Neutralise if the product calls for it. Residual acid keeps etching after you leave.

Brick is usually harder than the mortar holding it. Aim the fan at a joint and you will wash mortar out of it, which shows up as a line of pale, recessed joints and, on an old wall, as water getting in. Work the fan across the face of the brick rather than into the joints, and keep the tip square to the wall rather than raked along it.

If the joints are already soft, sandy or missing in places, the job is repointing and not cleaning. Say so, quote the clean for after the repointing, and let the customer decide.