Those Spots Are the Surface of a Deeper Colony
Black spots on interior walls in Las Vegas are mold in the overwhelming majority of cases. The coloration comes from the melanin pigment produced by certain mold species Cladosporium, Alternaria, and at higher moisture levels, Stachybotrys. The black spot on the wall surface is the visible face of a colony that is growing inside the wall assembly. What you can see is almost always smaller than what you cannot see behind it.
Scrubbing black spots with bleach removes the surface discoloration. It does not remove the colony. The hyphal structure of the mold penetrates into drywall paper and wood framing. Bleach on the surface kills what it contacts on the surface. The colony re-establishes from the material below within days to weeks. The spots come back.
What Causes Black Spots on Walls in Las Vegas
The location of the spots tells you the likely cause. Black spots at the base of an exterior wall usually mean moisture is entering from outside or condensation is forming on a cold wall surface. Spots near the ceiling line usually mean a roof or pipe leak above. Spots concentrated in one wall of a bathroom usually mean a slow plumbing leak or ventilation failure. A homeowner in Centennial Hills called us about recurring black spots on the wall behind their couch. The wall backed up to an exterior block wall with no insulation. Condensation from the temperature differential between the cooled interior and hot exterior was creating sustained moisture conditions on the interior face every summer.
What We Do
We inspect the affected area, identify the moisture source, and assess whether the colony has penetrated beyond the surface. Air sampling confirms species and concentration. If the colony is limited to the surface of a non-porous material, cleaning to standard is possible. If it has penetrated drywall paper or framing which is likely if the spots have been present for more than a few weeks removal is the correct approach. Read more about our mold removal service. Free inspection for property owners. Call (702) 442-1126.