Local Chimney Waterproofing in Jacksonville

What a repellent does and where it stops

Brick and mortar are porous, and a chimney takes rain on every face. A penetrating repellent changes the pores near the surface so they shed liquid water while still letting vapor out. The Brick Industry Association names chimneys among the brickwork most exposed to absorbing rain, where a repellent can earn its keep once the benefit is weighed against the drawbacks.

It does not close openings. BIA's note on clear coatings says penetrating repellents seldom stop water through cracks wider than 0.02 inch and cannot make up for failed caps, flashing or open mortar joints, so the repellent is the last step of a repair.

Chimney sealer or chimney water repellent

Products sold as a chimney sealer come in two families. Film formers such as acrylics, stearates, waxes and urethanes lay a skin on the surface that slows drying, and BIA warns that salts can crystallize under it and that an acrylic on damp masonry can turn cloudy. Penetrants soak in up to about 3/8 inch and coat the pore walls, so the wall can still dry.

BIA recommends only breathable coatings on exterior brick, measured for vapor transmission under ASTM E96, and suggests a siloxane or a siloxane and silane blend. That breathable kind is what we mean by chimney sealing. Silanes are small molecules suited to dense, alkaline surfaces, and siloxanes bond with the silica and alumina in brick. Both bond with unprotected glass, so nearby windows are covered.

Repairs first, and when they are enough

BIA lists the repairs a repellent should not replace: repointing open or crumbling joints, replacing spalled or cracked brick, renewing failed sealant and repairing flashing. On a chimney we add the crown and the cap. BIA also advises waiting several months after repairs before deciding a repellent is needed, because the repairs often solve the moisture problem, and a wall that has stopped darkening in rain can no longer show whether they worked.

Cure times and application

The data sheet for one siloxane chimney water repellent asks for new masonry to cure at least 28 days and 72 hours after repointing, which matches BIA's 72-hour minimum, and for clean, sound, visibly dry surfaces. BIA suggests test areas of at least 10 square feet, checked after they cure.

On vertical brick that data sheet calls for application from the bottom up with a low-pressure sprayer or a roller, flooding until the excess runs six to eight inches below the pattern, with a second wet coat soon after. BIA warns that over-application can reduce breathability. The crown takes a crown sealer, a different product.

Old coatings, efflorescence and the next coat

Penetrating repellents are typically incompatible with existing film-forming coatings, which may have to come off first. A wall with a history of efflorescence is treated only after the moisture source has been dealt with. Repellents require reapplication, and a splash test tells when: treated brick beads water, while brick that has lost its treatment darkens.

Our chimney waterproofing service ends with paperwork naming the product, the faces treated, the cure time we waited and the repairs that came first. Book a free inspection at (904) 920-5495 to find out if your brick needs a repellent at all.