Black mold in your basement: when to worry and what to do

You moved a shelf, or pulled back the carpet in the storage room, and there it is: a dark bloom across the drywall. Before you panic — or worse, blast it with bleach and forget it — here's how to think about what you're seeing.

"Black mold" — a quick reality check

Many mold species look black or dark green, and you can't identify one by eye. The infamous Stachybotrys gets the headlines, but the practical guidance is the same for all significant indoor growth: remove it, and fix the moisture feeding it. Any large indoor colony can affect air quality — allergy symptoms, irritated eyes and airways, musty odor — especially for kids, seniors, and anyone with asthma.

When DIY is reasonable

A patch smaller than about one square metre, on a hard, non-porous surface (concrete, tile, metal), with a moisture cause you've genuinely fixed: clean it with detergent and water, dry thoroughly, and watch it. Skip the bleach obsession — on porous materials bleach's water content can feed the problem while the surface just looks cleaner.

When to call a professional

• The patch is bigger than a square metre, or there are multiple patches
• It's on or in drywall, insulation, carpet, or wood framing — porous materials can't be surface-cleaned; growth extends inside them
• It keeps coming back after cleaning
• There's a musty smell but no visible source — growth is likely inside a wall or under flooring
• The basement flooded at some point and was never professionally dried

What proper remediation looks like

Real mold remediation follows a sequence: find and fix the moisture source first (there is no point cleaning mold that's still being fed); contain the area with poly and negative air so spores don't spread through the house; remove affected porous materials in sealed bags; HEPA-vacuum and treat salvageable surfaces; verify dryness with meters; then rebuild. In pre-1990s Calgary basements we test disturbed materials for asbestos first — mold and asbestos frequently live in the same wall.

The one rule that matters most

Mold is a symptom. The disease is moisture — a leak, seepage, condensation, or a past flood that never fully dried. Kill the moisture and mold can't return; skip that step and no amount of cleaning matters.

Musty basement? Dark patch spreading? We'll find the source and fix the whole problem — (403) 477-2281, serving Calgary and all surrounding communities.