Standard exterior paint on a chimney is one of the more predictable ways to accelerate masonry deterioration rather than prevent it. Chimneys are unique among exterior masonry structures because they handle moisture from two directions: rain and weather from the outside, and water vapor generated by combustion from the inside. A wood-burning or gas fireplace produces significant water vapor as a byproduct of combustion, and that vapor rises and migrates through the brick and mortar of the chimney structure. If the exterior is sealed with a film-forming coating that blocks vapor from escaping, that moisture is trapped within the masonry. In cold climates, trapped moisture freezes and expands during winter, spalling the brick faces and widening mortar joints. The correct product for a chimney surface is not paint. It is a vapor-permeable water repellent.

Inspecting Mortar Joints and Brick Condition Before Painting

No chimney coating project should begin without a thorough inspection of the masonry condition. Coating over compromised mortar or structurally damaged brick locks problems in place and obscures them from future inspection. The correct sequence is inspect, repair, then coat.

Start at the crown: the concrete cap at the top of the chimney that covers the space between the flue liner and the brick. This is the area most exposed to weather and the first to deteriorate. Look for cracks in the crown surface, separation between the crown and the flue liner, and missing or crumbled sections. A damaged crown allows water to run directly into the chimney structure rather than shedding off to the sides. ChimneyRx Brushable Crown Repair is an elastomeric coating specifically designed for this application. It bridges hairline cracks, forms a flexible waterproof membrane over the crown surface, and cures in two to four hours. For more severe crown damage with larger voids, use a hydraulic cement-based repair mix like Damtite before applying the flexible crown coating as a topcoat.

Mortar joints between bricks are the second critical area. Mortar has a significantly shorter lifespan than brick, typically 25 to 30 years versus the century or more that good brick can last. Look for joints that are recessed, crumbling, or show gaps. Probe questionable joints with a metal tool. If mortar crumbles or falls out when probed, repointing is required before any coating. Rake out deteriorated mortar to a depth of at least three-quarters of an inch, brush out dust, dampen the joint, and pack with appropriate chimney mortar mix in layers. Allow repointing to cure for at least a week before applying any water repellent.

Check brick faces for spalling: the flaking and breaking away of the brick surface layer from previous freeze-thaw damage. Spalled brick faces cannot be repaired effectively with surface coatings. Severely spalled bricks may need to be replaced before treatment. Surface staining from efflorescence, rust, or moss indicates active moisture movement and should be cleaned before treatment.

If the chimney has any previous paint or sealer on it, determine whether that coating is film-forming. Film-forming sealers on chimneys should be removed before applying a vapor-permeable water repellent, as the new treatment cannot perform through an existing sealed film. Test by sprinkling water on the surface: if water beads immediately, a film-forming sealer is present. If water absorbs within a few seconds, the surface is open to treatment.

Heat-Resistant Paint Considerations for Chimney Surfaces

The question of heat-resistant paint on chimneys is worth clarifying, because it applies to some parts of a chimney and not others.

The exterior brick and mortar of a chimney above the roofline does not get hot from the fire inside. The flue liner inside the chimney insulates the structure, and the exterior masonry surface stays close to ambient air temperature under normal operating conditions. The exterior is exposed to sun, rain, and wind, not to combustion heat directly. Standard masonry water repellents and coatings are fully appropriate for the exterior brick and mortar surfaces.

Heat-resistant paint is relevant for metal chimney components: the metal collar around the flue pipe where it exits a metal prefabricated chimney, the metal cap above the flue, and the sheet metal flashing at the roof-chimney junction. For these components, a high-temperature coating rated for the temperatures the specific component reaches is appropriate. Rust-Oleum High Heat and similar products are formulated for metal surfaces exposed to temperatures up to 1,200 degrees Fahrenheit and handle the intermittent elevated temperatures that metal chimney components experience.

The firebox interior, the visible interior brick surface behind the fire grate, is an area that does require high-heat paint if you wish to restore its appearance. Use a specifically rated fireplace paint for interior firebox applications, rated for temperatures above 1,200 degrees Fahrenheit. This is a completely separate consideration from the exterior masonry treatment.

Reaching and Painting Chimney Surfaces Safely on the Roof

Working on a roof near a chimney requires a different safety setup than standard ladder work on a wall. On a pitched roof, an extension ladder is not sufficient as the primary working platform. The roof surface itself is the working area, and moving along a pitched surface requires proper footing and fall arrest.

Roof bracket painting platforms are the right solution for chimney work on moderately pitched roofs. Roof brackets attach to the roof decking through the shingles, and a plank laid across multiple brackets creates a horizontal standing surface across the slope. Brackets are adjustable for pitch and provide a stable platform that supports full body weight and a supply bucket without shifting. For steeper roofs, a personal fall arrest system with a rope grab anchored to the ridge is the appropriate protection.

For two-story or taller chimneys that rise significantly above the roof surface, scaffolding erected around the chimney base provides a stable, full-perimeter working platform. Pump jack scaffolding with aluminum stages is practical for chimneys that need access on multiple faces.

Apply ChimneyRx or ChimneySaver Silane/Siloxane Water Repellent using a pump sprayer or an airless sprayer. Spray from the bottom of the chimney surface upward, applying the product in a wet, running bead that coats the surface uniformly. Apply the second coat within three to five minutes of the first while the first coat is still wet. This wet-on-wet application technique is specified by ChimneyRx to ensure full penetration into the masonry. Application requires dry conditions for at least two days before and after treatment, with temperatures above 50 degrees Fahrenheit. Cold temperatures slow absorption and can prevent proper penetration.

Do not apply water repellent in direct sun on hot masonry. The product evaporates too quickly to penetrate the masonry properly. Choose early morning or cloudy conditions when the brick surface is below 90 degrees Fahrenheit.

How to Paint a Chimney That Has Previous Coating Failure

Coating failure on a chimney that has been previously painted with a film-forming sealer presents one of the more difficult remediation situations in exterior masonry work. The existing coating is blocking vapor from escaping, moisture is trapped, and the coating may be peeling, bubbling, or crumbling at the surface. Simply applying another coating over a failing one repeats the problem.

The first step is removing as much of the failing coating as practical. Wire brush the entire surface to remove loose and flaking material. A wire wheel on an angle grinder speeds this process on flat brick faces, but care is needed near mortar joints to avoid damaging sound mortar. For very thick film-forming coatings, a pressure washer at 2,000 PSI with a 15-degree nozzle tip can assist in removing loose sections. Allow the surface to dry completely after pressure washing.

After removing the failed coating, assess what remains. If a thin layer of old coating remains bonded firmly to the brick and resists removal by wire brush, apply a masonry paint stripper and allow it to dwell according to the manufacturer’s instructions before pressure washing again. Chemical strippers designed for masonry, such as Dumond Smart Strip Pro, are effective on multiple paint layers.

Once the surface is as clean and open as can be achieved practically, inspect the mortar joints and perform any necessary repointing repairs. Allow all repairs to cure for at least seven days.

After the surface is clean, repaired, and dry, ChimneySaver or ChimneyRx Silane/Siloxane Water Repellent is the appropriate coating. These products penetrate into the masonry surface and create water repellency within the pores of the brick and mortar rather than forming a film on the surface. The key property is 100 percent vapor permeability. Combustion moisture generated by the fireplace can still migrate outward through the masonry, but rain and external moisture cannot penetrate in. This is the only type of treatment that is compatible with an active chimney’s moisture dynamics.

For chimneys with significant structural concerns, including large sections of spalled brick, severely deteriorated mortar that would require extensive repointing, leaning or out-of-plumb chimney structures, and active water intrusion into the firebox, hiring a CSIA-certified chimney specialist before any coating work is the correct decision. Coating work on a structurally compromised chimney masks problems rather than solving them.