Mold is the point where a water loss stops being a construction problem and becomes a health and liability problem. It is also the point where we hand the job to somebody else and wait, which is not what most homeowners expect a contractor to say.
- Mold can begin growing in damp building materials within roughly 24 to 48 hours. Drying speed is the whole game.
- In California, visible mold in a dwelling is a substandard housing condition by statute under SB 655, which matters enormously for rentals.
- Remediation happens under containment, by a certified crew with pollution liability coverage. We do not self-perform it, and we do not rebuild until it is cleared.
- California has no mold specific contractor license and no state mold exposure limits, so certification and insurance are what you actually check.
Why mold shows up so fast
Mold spores are already in every building. They need moisture and an organic food source, and a wet house supplies both: paper faced drywall, wood framing, cellulose insulation, dust. Under the right conditions, growth can begin in damp materials within about 24 to 48 hours. That is why the emergency response to water damage is measured in hours and why every day a wall cavity stays wet raises the odds that a drying job becomes a remediation job.
The most common mold we find in Bay Area homes is not from a dramatic flood. It is from a slow leak nobody knew about: a shower pan, a supply line inside a wall, a drain under a slab, a bathroom with no working exhaust fan. By the time there is a stain on the drywall, the cavity behind it has been wet for a long time.
What California law actually says
California takes an unusual position here. There is no state mold specific contractor license, and the state has never adopted permissible exposure limits for indoor mold, despite the 2001 Toxic Mold Protection Act contemplating them. So there is no official number that says a house is clean.
What California does have is SB 655, effective January 2016, which amended Health and Safety Code sections 17920 and 17920.3 to make visible mold growth a form of inadequate sanitation and therefore a substandard building condition. Minor mold on surfaces designed to get wet, like a shower, is excepted. The practical effect: for a rental property, visible mold is now a code enforceable habitability defect, and a landlord who has notice and does not act is exposed. Civil Code 1941.7 sets when that obligation is triggered.
If you own a rental in San Jose, that is the sentence to remember. We cover the operational side in water damage for property managers.
How remediation is supposed to work
Real remediation follows the IICRC S520 standard and looks like this: find and fix the moisture source first, because remediation without that is temporary. Set containment with plastic barriers and negative air pressure so spores are not distributed through the rest of the house. HEPA filtration in the work area. Remove contaminated porous materials, drywall, insulation, carpet, rather than trying to clean them. HEPA vacuum and wipe the remaining structure. Dry it fully. Then verify.
Two things distinguish this from a bleach and a Saturday. Containment, which is what keeps a bathroom problem from becoming a whole house problem. And verification, ideally by an independent indoor air quality professional rather than the company that did the removal, since a firm testing its own work has an obvious conflict.
Supraclean handles this side in San Jose. They are IICRC certified, carry the pollution coverage, and run containment properly. They also do the crawl space and sewage work that shows up alongside mold in older homes.
Why we will not do the remediation ourselves
Standard commercial general liability policies carry an absolute pollution exclusion, and California courts have treated mold and indoor air contaminants as pollutants under it. A general contractor who self-performs mold removal without contractors pollution liability specifically endorsed for mold is uninsured for the exact claim most likely to arise: that the work spread contamination or did not fully remove it.
So we do not do it. We rebuild after it is done and documented. It costs us revenue and it is the right structure for the homeowner, because both halves end up covered by the right policy.
The rebuild after remediation
Once clearance is documented, the rebuild is ours: insulation, drywall, texture matched to the surrounding wall, paint, trim, flooring, and rebuilding whatever cabinetry or tile came out. Two details matter more than they look:
- Fix the cause, not just the damage. If the mold came from a missing or undersized bathroom exhaust fan, or a fan venting into an attic instead of outdoors, then rebuilding without correcting the ventilation guarantees a repeat. Same with a shower that was never properly waterproofed behind the tile.
- Waterproof the rebuild properly. Tile and grout are not waterproof. The membrane behind them is, and it is invisible once tile goes on, which is exactly why a rushed crew skips it.
We will not build over material that has not been cleared. It is the one part of a schedule we do not compress, because building over mold means opening the same wall twice and the second time is on somebody's conscience.
What to check before you hire anyone
- IICRC certification for the remediation firm, and ask which standard they work to.
- A certificate of insurance showing active pollution or mold coverage, not just general liability.
- A written protocol: containment, negative air, HEPA, source correction, and how clearance is verified.
- Independent post remediation verification rather than self certification.
- For the rebuild, a CSLB licensed contractor. You can verify any California license number on the CSLB site in about a minute.