Why is there white powder on my basement wall?

White powder on a basement wall is usually efflorescence: mineral salts left when water moves through concrete or masonry and then evaporates. It is evidence of a moisture path, not mould and not a decorative stain. The water may be a slow seep, condensation, or an old leak that is now dry. Brushing it off without finding the moisture source means it comes back. In Ontario that source is often rain, spring thaw, or humid air on a cold wall.

Where the water shows up

What to do now

Note whether the powder returns after you dry-brush it, and whether that follows rain or stays in summer humidity. Run a dehumidifier if the air is damp, but treat recurring powder after storms as a water-entry clue.

When to call a contractor

Call when powder keeps returning, when the wall is damp to the touch, or when you also see peeling paint, a crack, or a musty finished basement. A contractor should say whether this is condensation, a crack, or drainage.

Start with the provincial guide water in the basement, then the Ontario cost hub.

Local basement waterproofing guides

• Burlington basement waterproofing
• Hamilton basement waterproofing
• Oakville basement waterproofing
• Toronto basement waterproofing
• Mississauga basement waterproofing