White Crust and Small Icicles on a Garage Ceiling

That crust is minerals from inside the concrete. Water gets into the deck above through a crack or a worn joint, picks up minerals on its way down through the slab, and leaves them behind where it drips out and dries. The small icicles grow the same way, one drop at a time.

The crust itself does no harm. The water does. It is passing all the way through the slab, and in a garage in February it carries road salt. Salt water that keeps reaching the steel inside the deck is how rust stains on a garage ceiling start.

Look up as you walk the garage. Note where the crust lines up with a crack or a joint, then find the same spot on the deck above. If brown or orange stain shows up in the white, the water has already reached the steel.

The repair works from the top. Sealing the crack or replacing the joint seal stops the water, and the slab can dry out. It is a far smaller job now than after the steel starts to rust.

We fix this: Parking Garage Restoration