Local chimney waterproofing in Nassau Village-Ratliff

Absorption through the faces versus water through openings

Masonry takes on water in two distinct ways. Rain can soak slowly through the faces of brick and mortar, spreading as a dark, damp patch across a whole wall. Or it can run in through a specific opening: a crack, an open joint, a failed crown or a gap along the flashing. The Brick Industry Association treats clear repellents as a tool for the first problem, reducing how much the faces absorb, and says little can be expected of them against the second.

So on a chimney we sort the two before anything is proposed. Openings are repaired with mortar, brick or metal. Absorption through sound faces is what a treatment is for.

Silanes on dense surfaces

Of the clear repellents, silanes have the smallest molecules. BIA's note explains that the small size helps them get into dense materials, and that they are supplied at high concentrations of active ingredient. The reaction that makes them water-repellent goes fastest on alkaline surfaces like concrete and concrete block, which act as their own catalyst.

On less alkaline clay brick, some products carry an added catalyst to help. Where a chimney has a very dense brick, a block section, or a concrete element that needs treatment, a silane or a blend led by silane may suit it better, and we explain the choice made.

More is not better

A heavier coat of repellent can seem like better value. BIA's note says the coverage rate is critical, because putting on too much can cut the breathability of the masonry, and breathability is the whole reason for choosing a penetrant over a film. The maker of the product we use gives a coverage range per gallon that depends on how porous the surface is, and very dense brick takes less than soft brick. We work within that range, keep track of how much each face has taken, and record it in the job notes so the next treatment can be planned from real figures.