Local chimney waterproofing in American Beach

The crack width a repellent will not bridge

A penetrating treatment lines the pores of the masonry; it does not fill a gap. BIA's clear-coatings note draws the line precisely, saying these products seldom keep water out of cracks more than 0.02 inch wide. That is about half a millimeter, roughly the thickness of five sheets of printer paper stacked together.

Wider openings, such as an open head joint, a cracked brick or a separation under the crown, pass water straight by the treated surface around them. Those are fixed with mortar or new units first. The treatment, if it still makes sense, comes once the wall is closed.

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.

Water-based or solvent-based repellent

The active ingredient in a clear repellent is delivered in a carrier, either water or a solvent, that evaporates after the product has soaked in. BIA's note says the choice of carrier changes the conditions a product can go on in, and points out that green building programs set limits on solvent content. The two kinds also differ in odor, in clean-up and in how they behave on dense or damp surfaces. The product we name states its carrier, and we follow its limits on surface moisture, temperature and ventilation. The choice is explained if a solvent-based product is proposed.