How to Clean Painted Brick Without Lifting Paint

Why painted brick is cleaned differently from bare brick

Bare brick is one of the more forgiving surfaces on a house. It takes pressure, and the part to look after is the mortar, not the brick. Painted brick is a different job, because the surface you are cleaning is the paint.

Masonry paint sits on a rough, porous surface that takes in and gives off moisture. The bond is partly mechanical and it is never even. It changes from brick to brick, it is weaker over old repointing, and it is weakest wherever moisture moves through the wall. High-pressure water finds those weak spots at once, gets under the film, and peels back a patch much larger than the spot where it entered. The result is a bright square of raw brick in the middle of a painted wall. That is a repaint, not a touch-up.

There is a second problem. Paint slows how fast a brick wall dries to the outside. If moisture already moves through the wall from behind, the paint is under pressure from the inside, and washing at any pressure speeds up a failure that was already coming. Seeing that before you start is most of the job.

Check the paint before you clean

Walk the wall in good light and do these checks on each side of the house:

• Tape test. Press painter's tape firmly onto the paint in several places and pull it off fast. If paint comes away on the tape, the film is already letting go.
• Chalk test. Rub your hand across the wall. A powder on your hand means the paint is oxidizing and near the end of its life.
• Blisters. Small raised bubbles mean moisture is behind the film. That is a water problem, not a dirt problem.
• White deposits. A white powder pushing through the paint is efflorescence, covered below. It means water moves through the brick.
• Mortar. Original lime mortar, modern repointing, and painted-over joints all behave differently. Soft or crumbling mortar rules out pressure at any setting.
• Coats. Many layers of paint over decades stick less reliably than one recent coat, and the old layers can be a different type of paint than the top one.
• Coating type. Elastomeric coatings, limewash, mineral paint, and standard acrylic masonry paint each take cleaning differently. Limewash in particular is made to wear slowly, and a strong rinse removes it. If you know which coating is on the wall, tell whoever cleans it.

If two or more checks fail on the same wall, stop. That wall needs a painter's opinion before it needs a wash.

How to clean painted brick, step by step

1. Pick a test area that does not matter: a back wall, a spot behind a shrub, a section beside the garage. Not the front of the house.
2. Make it large enough to judge, at least a few square feet across several brick courses and a mortar joint.
3. Soak the plants below and around it, and cover anything the solution must not touch.
4. Close the windows near the area, and cover outlets and light fixtures.
5. Wet the wall. A wet wall takes the cleaner more evenly and does not streak as fast.
6. Apply the cleaning solution at the strength you plan to use for the whole house, from the bottom up, and give it the dwell time you plan to use. A test that is gentler than the real job tells you nothing.
7. Rinse from the top down with a wide fan tip, a few feet back from the wall.
8. Let it dry fully. This is the step people skip. Wet masonry looks even. Streaks, blotches, a dull patch, or lifted edges only show once the wall is dry, and brick can take a full day to dry.
9. Look at it in the light you will judge the finished wall in, in sun and again in shade.
10. Then decide. If the test area came out clean and the film is intact, do the rest of the wall the same way. If anything lifted, changed sheen, or streaked, change the method.

On painted brick, we soft wash with sodium hypochlorite and a surfactant, cut with water to suit the coating. We do not use pressure to clean the paint. We soak the plants below the wall with water before the solution goes on, and we rinse them again after.

Can you pressure wash painted brick?

Not at the pressures used on concrete or bare masonry. High pressure lifts paint wherever the bond is weak, and on an older wall you cannot see where that is until it lets go.

Soft washing is the method that works. A cleaning solution matched to the growth and the coating goes on at low pressure, stays long enough to break down algae, mildew, and road film, and then a low-pressure rinse takes it off. The solution does the work, and nothing pushes against the paint bond. Our guide to soft washing versus pressure washing explains where each method belongs.

A rinse with a wide fan tip held a few feet back is fine on sound, recent paint. The number that matters is the pressure that reaches the wall, not the number on the machine. Pressure drops quickly with distance and a wider tip angle. A pressure washer that reaches 4,000 PSI is the right tool for a driveway. On a painted wall it is only a rinse, and only from a distance.

Hand cleaning with a soft brush covers small areas, the trim around windows and doors, and any section where the tape test came back poorly.

The solution matters as much as the pressure. Some cleaners that are fine on vinyl dull or stain a masonry coating, and bleach mixes need careful dilution and a full rinse on painted surfaces. Ask what will go on your wall, and at what strength.

What causes white powder on painted brick?

Efflorescence. Water moving through the brick dissolves salts in the masonry and the mortar and carries them to the surface. When the water dries, the salt stays behind as a white powder or crust. On painted brick it often pushes the paint off from behind.

A wash removes the powder, but not the water that brings it. It comes back until the water source is fixed. The usual sources are a gutter that overflows, a downspout that empties against the wall, soil or mulch piled above the base of the wall, a cracked cap on a chimney or a garden wall, or a leak inside.

Brush loose efflorescence off with a dry, stiff brush before you wet the wall. Flooding it with water dissolves more salt and brings it back to the surface as the wall dries.

Mistakes that cause peeling, streaks, or a dull finish

• Treating painted brick like bare brick. The most common error and the most expensive.
• Putting cleaner on dry painted masonry from the top down. The cleaner runs down in streaks, and on some coatings the streaks do not rinse out.
• Letting the solution dry on the wall. On a hot, sunny wall the working window is short, and dried cleaner leaves a residue you can see.
• Rinsing only part of the way. Residue left in the brick texture and the mortar joints comes back as haze once the wall dries.
• Ignoring the mortar. A method that is safe for the paint can still strip soft joints, and the joints are usually the oldest thing on the wall.
• Cleaning a wall with active efflorescence and calling the job done.
• Judging the test area while it is wet. A wet test is not a test.

When the wall needs paint, not a wash

Do not wash a painted wall that fails the tape test across large areas. Water and solution get under the loose film, and the wall comes out patchier than it went in. That wall needs scraping and paint, and the wash is part of the paint prep, not a substitute for it.

For a sound coating, ask a cleaner these questions before you hire one:

• Will you tape-test the paint and do a test area before the whole wall?
• What solution will you use on a painted masonry coating, and at what dilution?
• What rinse pressure will you use, and how is it different from what you use on concrete?
• How will you handle the mortar joints, mainly any repointed sections?
• If the test area lifts paint, what happens next?

A contractor who treats the test area as standard practice has cleaned painted masonry before. One who gives a flat price to wash the house without asking if the brick is painted has not. Our home exterior cleaning site assessment lists what a cleaner checks on each wall before the work.

House washing from us on painted brick starts with the tape test and a test area, then a soft wash. If the paint is failing, we tell you before any work starts. Text a photo of the wall to (610) 665-3995. We reply within 24 hours.