Mold and Dark Spotting on Stucco
Stucco holds moisture in its texture, which makes it one of the most mold-prone surfaces on a Florida home — and one of the easiest to damage while trying to clean it.
Telling the three common problems apart
Mildew appears as diffuse grey-to-black shading, worst on shaded elevations and under overhangs. It wipes partially with a wet cloth and covers broad areas rather than forming distinct dots.
Artillery fungus shows as tiny, hard black dots, usually only on the lower few feet of wall. It grows in hardwood mulch and shoots spores several feet onto the wall, where they cement themselves. It does not wipe off.
Efflorescence is the opposite problem — a white chalky bloom of mineral salts pushed out from inside the stucco by moisture migration. It signals water getting into the wall, and cleaning it without addressing the source only buys time.
Why stucco is difficult
The texture that gives stucco its appearance also gives mold enormous surface area and shelter. Organisms sit down in the profile where rinsing cannot reach them.
Stucco is also more fragile than it looks. The finish coat is thin, and high pressure chips it, exposes the base coat and creates a patch that will never blend.
Worse, driving water into stucco under pressure pushes moisture behind the finish. On a wall system with any existing crack or flashing issue, that turns a cosmetic problem into a moisture problem inside the wall.
What not to do
Do not pressure wash stucco. There is no upside. It damages the finish and drives water where it should not go.
Do not paint over mold. It grows through new paint within a season, and now you have a bonded layer of stained paint to deal with instead of surface growth.
Do not ignore hardwood mulch against the house if you have artillery fungus. Until the mulch is replaced with rubber, stone or pine bark, the spotting returns every season no matter how well the wall is cleaned.
How we clean stucco
Soft washing, always. Low pressure with a cleaning solution that penetrates the texture and kills growth at the root, given proper dwell time before a thorough rinse.
We treat full elevations rather than spots, so the wall dries evenly and you do not end up with a clean patch surrounded by dirty stucco.
Where we see efflorescence or a moisture source, we will point it out. We clean exteriors — we do not do stucco repair — but you should know if the wall is telling you something more than cosmetic.
Questions we get about this
Can artillery fungus spots be fully removed?
Will soft washing damage stucco or its paint?
What is the white chalky residue on my wall?
How long until mold comes back?
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