Chimney Waterproofing in Connecticut

This is a different problem from a leak. A leak is water finding a route in through a crack, a failed flashing or an open joint. Absorption is the masonry itself taking up water like a sponge, across its whole surface, and then releasing it — outward in dry weather, inward when it cannot.

In Connecticut that matters because of what happens next. Water inside brick that then freezes expands, and the expansion takes the face off the brick. Repeated across a winter and across years, that is spalling, and spalling does not reverse.

Waterproofing is a treatment applied to sound masonry that dramatically reduces how much water it absorbs while still letting vapour out. The second half of that sentence is the important one.

The materials used for this are vapour-permeable water repellents — typically siloxane or silane-based — which line the pores of the masonry rather than film over the surface. Water beads and runs off; vapour still passes outward.

What must not be used is a film-forming sealer: paint, acrylic sealant, or anything that puts a skin on the brick. Masonry always contains some moisture, and a stack that cannot release it holds it instead. Come the first hard freeze, the trapped water expands behind a sealed face and takes the brick with it. A sealed chimney deteriorates faster than an untreated one.

The other precondition is that the masonry is sound first. Treating a stack with open joints or a cracked crown seals nothing useful — the water is coming in through the gaps rather than through the brick. Repointing and crown work come first; treatment is what protects them afterwards.