Crete: why we told a homeowner not to paint the chimney
The brick was spalling and the homeowner wanted to seal it with paint. That would have finished the chimney off. Here is what we did instead.
The chimney
A 1970s two-story in one of Crete’s subdivisions, exterior chimney on the north side, brick faces popped off in a band about four feet above the roof. The homeowner had a can of masonry paint and a plan. We asked them to wait a day.
Why paint makes it worse
Brick is porous. It takes on water in rain and gives it back as vapor when the sun comes out. Freeze-thaw damage happens when water is inside the brick when the temperature drops; the ice expands and pops the face. Paint and acrylic sealers form a film on the surface. Water still gets in, through hairline cracks, through the mortar, through the crown, but now it cannot get out as vapor. It freezes behind the film, and the next spring the paint comes off in sheets with the brick face attached. We see painted chimneys in Crete that are in worse shape than the unpainted ones next door for exactly this reason.
What we did
First the water source. The crown was cracked and got a crown coat; the cap was missing and got a stainless one. Then the damage: we cut out the spalled bricks and replaced them with matched brick, and repointed the joints in that band with a Type N mortar. Then the protection: a silane-siloxane water repellent, sprayed on the dry chimney. It soaks into the brick and lines the pores so liquid water beads off, but it is not a film; vapor still passes through and the chimney can dry. It is invisible, lasts about ten years, and it is the only kind of sealer we put on masonry. The paint went back to the store.
If this sounds like your house: we handle chimney masonry repair and waterproofing across Kankakee County, and our Crete page covers what we usually find there. Call (815) 449-4264, 7am to 9pm, any day.
Quick questions
Can a chimney be painted safely?
Not with ordinary paint or film sealers. If a color change is wanted, a mineral silicate stain that stays breathable is the only option we would consider.
What is a breathable water repellent?
A silane or siloxane product that penetrates the brick and repels liquid water while letting vapor escape.
How long does siloxane last?
Roughly ten years, then a fresh coat.
Should I waterproof before or after tuckpointing?
After. The repellent protects the new mortar and the repaired brick together.
Published October 8, 2026 · By Jacob Dove, Friendship Chimney Sweep, Bourbonnais IL