How much mold can you remove yourself?

The working threshold, from EPA guidance, is about ten square feet: roughly a patch three feet by three feet. Below that, on a hard or easily replaced surface, with the moisture source already fixed, it is a reasonable job to do yourself. Above it, or anywhere inside the building fabric, it needs containment and negative air pressure, because disturbing a colony is what moves it into the rest of the house.

That number is guidance rather than a rule, and four things override it.

What overrides the size

Who lives there. If anyone in the house has asthma or a chronic lung condition, is immune compromised, is on chemotherapy, is an infant, or is pregnant, hand the work to someone else regardless of the size. The person doing the disturbing takes the largest exposure.

Whether the water is fixed. Removing growth while the leak is still running is redecoration. Fix it first, always.

What it is growing on. Hard, non-porous surfaces clean: tile, glass, sealed metal, solid plastic, glossy paint on sound plaster. Porous ones do not: drywall, bare wood, insulation, carpet, ceiling tiles, particleboard. Ten square feet of growth on drywall is not a cleaning job even at that size, it is a small removal job.

Whether it is inside something. Wall cavity, under a floor, in ductwork, in insulation, in a crawl space. Size stops being the question once it is not on a surface you can see all of.

Doing a small one properly

1. Fix the water. Not optional and not last.
2. Shut the room off. Close the door, put a towel along the bottom, and open a window if the weather allows. If there is a vent or return in the room, cover it.
3. Do not run a fan into the house. A fan in the window blowing out is fine. A fan on the floor blowing around the room is how it spreads.
4. Wet it slightly first, with water or a detergent solution in a spray bottle. Dry scrubbing sends the most into the air.
5. Scrub with detergent and water. The physical removal is the part that works. Not bleach on porous material, which takes the color out and leaves the growth.
6. Bag porous material as it comes out, sealed, before carrying it through the house.
7. Dry it properly. The surface, and the material behind it. This is what stops it returning.
8. Clean up with a HEPA vacuum if you have one. An ordinary vacuum without a HEPA filter passes spores straight through and redistributes them.
9. Wash yourself and the clothes afterwards.

Do not paint over anything until it is clean and dry. Mold resistant paint stops growth starting on a clean surface. Over an existing colony it is a lid.

What a professional job looks like

If you are paying for it, this is what you are paying for, and it is worth checking you are getting it:

• Containment: plastic sheeting sealing the work area, often with a zipped entry.
• Negative air pressure, so air flows into the contained area and out through a filtered exhaust fan to outside, rather than into the rest of the house.
• HEPA air scrubbers running during the work and afterwards.
• Removal of porous material, cut back beyond the visible growth.
• HEPA vacuuming and damp wiping of what remains.
• Drying to a measured target, with a meter, not a judgment.
• Clearance verification afterwards, ideally by someone who did not do the work. Which is the one test genuinely worth paying for.

Two things that should make you ask questions. A quote that offers to spray or fog a treatment as the whole job: dead growth in a wall is still material that comes out, and the moisture is untouched. And a quote with no mention of finding and fixing the water source.

Things not to bother with

• Ozone generators. Sold for this, not effective for it, and ozone is a respiratory irritant. Do not use one in an occupied building.
• Fogging as a standalone treatment. See above.
• Bleaching porous material. Cosmetic.
• Painting over it. Cosmetic, and it makes the next inspection harder.

After it is gone

It comes back if the conditions come back. What actually keeps it away is humidity and ventilation, which is a maintenance question rather than a remediation one: what to change so it does not return.

The short version

About ten square feet, hard or replaceable surface, water already fixed, nobody vulnerable in the house: yours. Bigger, porous, or inside the fabric: contained. Wet it before you scrub, use detergent rather than bleach, bag porous material before carrying it out, and dry to a meter reading rather than to a feeling.