Always clean from the bottom up, so that spent cleaner doesn’t trickle down dry, absorbent surfaces.
1. Soak the surface with clean water. Also called “prewetting.” This fills the masonry pores with water and keeps the cleaner on the surface where it does its job of dissolving the contaminants and soiling.
2. Apply the cleaner. This is done with a low-pressure sprayer. Pump-up sprayers, similar to those used in gardens, but modified for acidic products are often used. You can use a bucket and brush, but the sprayer is more efficient.
3. Dwell and agitate. Leaving the cleaner on the surface for a few minutes – called “dwell time” – gives it time to dissolve excess mortar and other soiling. Gentle scrubbing with a brush helps the cleaner break dried deposits from the surface. Hard scrubbing isn’t needed under most circumstances – the cleaner should do most of the work.
4. Rinse the spent cleaner and dissolved contaminants from the wall. The wall should be thoroughly pressure-washed with fresh water, but at no more than a few hundred psi. The important factor in rinsing is gallons per minute (gpm). Four to 8 gpm is usually appropriate, until the wall stops foaming. Then start the process again on the next section of wall.