Local chimney waterproofing for Middleburg homes

How deep a penetrating repellent goes

The protection from a penetrating product sits beneath the face of the brick. BIA puts the depth at up to about 3/8 inch for penetrants in general, with no film left on the surface. The maker of the siloxane we use states penetration of up to 1/4 inch or more, varying with how porous the surface is and how much moisture it holds on the day. That depth is what lets the treatment outlast wear of the outer face. It is also why the brick has to be dry: pores already full of water leave less room for the product to travel, and the treated zone ends up shallower.

Waiting after the joints are repointed

New mortar in a joint is still hardening and still giving off water for days after it is placed. Coating it too soon can interfere with that cure and lock the moisture in. BIA's pre-coating checklist sets a floor of 72 hours for freshly repointed mortar and repaired sealant joints, and the maker of the repellent we use sets the same interval after tuckpointing or other repairs.

On a chimney that has just been repointed, treatment is therefore booked as a separate visit. Writing the cure period on the estimate keeps anyone from spraying on the same afternoon the trowels are put away.

Applying from the bottom up

On a vertical face, the maker's directions for our product start at the bottom and work upward, using a low-pressure sprayer with a fan nozzle or a roller. Each pass floods the brick until a little excess runs down below the wet area, and a second wet application follows within minutes, before the first has soaked away. Starting low means any run-down falls onto brick that has not been treated yet, instead of streaking across finished work. Each face is completed in one continuous session so there are no lap marks where one day's work meets the next. Corners and the edges of the crown are cut in by brush where the spray cannot reach cleanly.