Black Mold vs Mildew: How to Tell the Difference in Your Basement

"Is that black mold?" — it's the question we get asked on at least half of our Markham basement inspections. Here's a clear answer.

Mildew

Surface-level. Usually grey-white or yellow. Wipes off easily. Common on shower grout and damp surfaces. Annoying but rarely a serious health hazard if cleaned promptly.

Black mold (Stachybotrys chartarum)

Slimy or fuzzy. Dark green-black. Grows on wet cellulose materials — drywall, wood, insulation paper. Produces mycotoxins linked to severe respiratory issues. Cannot be cleaned with bleach if it's in porous material — affected material must be removed.

How to tell at home (rough guide, not a diagnosis)

If it wipes off and the surface underneath is clean, it's probably mildew. If it returns within days, has a musty smell, or grows on drywall/wood/insulation, treat it as serious mold and stop touching it without protection.

The only permanent solution

Stop the moisture. No matter what species you have, mold needs water to live. Waterproofing your basement removes the food source — without it, no remediation lasts.

Get a free inspection in Markham

If you've noticed dampness, cracks, or musty smells in your basement, don't wait. We offer free on-site inspections across Markham, Unionville, Cornell, Berczy Village, Cathedraltown, Markville and Thornhill — and our work is backed by a written workmanship warranty.