Efflorescence on the foundation: what it is, how serious, what it costs

It is a white, powdery or crystal-like deposit on concrete, brick or mortar. Water moves through the material, dissolves the salts in it, then evaporates at the surface and leaves those salts behind.

You mostly see it on basement foundation walls and on exterior brick. To tell it apart from mould: efflorescence dissolves in water and crumbles between your fingers, and it does not grow on wood or drywall.

Efflorescence itself is harmless. What it tells you is that water is getting through the wall. A few old, dry traces on a concrete foundation are common.

It becomes serious when it comes with dampness to the touch, water stains, cracks or crumbling concrete, or when a finished basement hides the wall. In analyses, I usually put it under “To check”: the real question is where the water comes from.

The deposit is brushed off dry, then monitored: $200 to $450 for one area. A downspout that empties at the foot of the wall can be extended for $100 to $250. If water comes in through a crack or a weak spot, sealing the leak costs $400 to $1,000 per spot.

The real cost depends on the cause: a gutter is a small fix, a foundation drain at the end of its life is a much bigger one.

These are ballpark figures for Quebec, to be confirmed with quotes.

1. Was the wall damp to the touch, and did you take a moisture reading?
2. Were there water stains, cracks or crumbling concrete in the same spot?
3. Do the grading, gutters and downspouts send water toward this wall?

Does your report mention efflorescence? Upload it: in five minutes, I tell you what comes first, what to have checked and what to ask the seller.

No. It is a deposit of mineral salts with no health risk. It dissolves in water and crumbles, while mould grows on materials like wood or drywall paper. Both can share the same cause: moisture.

The deposit, no: it can be cleaned. What matters before lifting the inspection condition is knowing where the water comes from and whether it still gets in.