Apr 192013

This crown is thin and cracked, and has worn away along the edges.

Just as your house needs a roof to keep water from entering, so does your chimney. Chimney crowns are simply the mortar “roofs” of masonry chimney systems. Poor crown construction is a leading cause of chimney deterioration due to the entry of water into the system through the faulty crown. Water entry into a masonry chimney causes freeze-thaw erosion, mortar deterioration, spalling (flaking), and efflorescence (mineral deposits on the surface of brick), and will eventually destroy the chimney.

This crown has almost entirely worn away!

Like the sloping roof of a house, the chimney crown should slope down from the flue liner. Flat crowns or those with minimal slope can allow water to enter the interior of the chimney. Crowns should be poured at least two inches thick at their thinnest point. Thin crowns do not have as much resistance to water as a properly poured crown and tend to wear away and crack much faster, allowing water entry. A chimney crown should extend a minimum of 2 and 1/2 inches beyond the face of the chimney on all sides. This overhang helps to keep water from running down the chimney face.

This crown is almost gone at the edges, exposing bare brick.

This crown has cracks running through it, and chipped edges. It is not water tight.

If your crown has deteriorated, Barnhill Chimney can repair it. If it has only minor cracks and is otherwise in good shape, we may just recommend you install a full size chimney cap to protect it from further weather-related wear and tear. If it has a lot of cracks or is a little chipped around the edges, we can seal it. Sealing the crown restores its original water resistant state and can greatly prolong the life of your chimney.

Our product of choice, CrownCoat, is a premixed, trowel grade, elastomeric coating that forms a flexible waterproof membrane to protect chimney crowns and more. It cures in about 24 hours to a natural concrete/mortar appearance. It is used on chimney corbels, the tops of masonry and parapet walls, or wherever a flexible waterproof membrane is needed. CrownCoat can be colored using standard mortar dye.

We do not use tar to seal any part of the chimney. Tar does not expand and contract along with the chimney, so it tends to crack and fall away very quickly, often within only a year or so. CrownCoat (and related products) are designed for use on chimneys and can last many years.

If your crown looks like some of the photos above, or has worn away completely, we may have to build a new crown. Our chimney crowns are constructed using cast-in-place reinforced concrete. They are built a minimum of four inches in thickness. We use industry- and application-appropriate materials, and take care to protect your roof during installation.

A chimney in need of a crown (and some brick repair to the left side).

A wooden framework is laid and leveled, and slowly filled with mortar.

The fully poured crown. Note the slope for water runoff.

The finished product, complete with overhang (and brick repair!).


Apr 192013

A masonry chimney showing severe water damage.

Over time, water “eats” masonry chimneys. Mortar joints between bricks are dissolved by water; bricks are slowly broken apart by water moving inside the brick. Water moving within bricks causes effluorescence (mineral deposits on the outside of bricks, brought from the inside by water movement) and spalling (flaking or chipping of brick, caused by water freezing inside the brick and expanding, causing pieces of brick to flake away). Deteriorated masonry allows water to enter the chimney structure, causing more damage.

Masonry chimney showing effluorescence, spalling, cracking, and flaking due to water entry.

Masonry chimney showing effluorescence, spalling, cracking, and flaking due to water entry.

There are multiple ways to prevent or mitigate water damage. The most important is to have a good quality chimney cap, which protects the flue and the top of the chimney from water entry. The second most important is to keep your masonry in good repair. A waterproofing treatment can help seal masonry chimneys against water entry without changing the appearance of the masonry. There are several different kinds of waterproofing agent. Our favorite right now is made by Professional Products of Kansas:

PROFESSIONAL® Water Sealant has been manufactured since 1987. It is a RTV silicone rubber water repellent that has been successfully applied to buildings, bridges, highway sound walls, decks, fences, and many other types of surfaces in cities and towns in North America and abroad to protect against water intrusion and/or graffiti. PROFESSIONAL® Water Sealant is an inorganic sealant that bonds naturally to a variety of surfaces. Once applied it creates a long lasting, invisible barrier preventing damage caused by moisture.

PROFESSIONAL® Water Sealant provides your structure with the best protection money can buy … only nature protects better.

Mossy chimney

This chimney is covered in moss, evidence that the masonry structure is holding water.

Professional Water Sealant is recognized as an industry standard by architects, engineers, contractors, and building owners for its superior above grade water repellent capabilities. It is an extremely long lasting, penetrating, water repellent product formulated by using RTV silicone rubber.

  • Transparent Dries to a clear, flat finish.
  • Quick Drying Starts to cure within 2 hours.
  • Seals Any Porous Substrate Developed for use on above grade horizontal and vertical surfaces such as: brick, block, concrete, and stone.
  • Long Lasting Waterproofing Protection Penetrates into the capillary system to permanently bond with the substrate.
  • Durable…Non-Sacrificial Because silicone rubber is inorganic, there is no deterioration from ultraviolet rays, ozone, salt spray, acid rain, etc.
  • 400% Elongation Expands and contracts with building movements and temperature extremes…bridging hairline cracks.
  • Breathable…High Perm Rate Allows moisture vapor to escape while prohibiting liquid penetration.

Waterproofers can be applied only when the weather is above about 40 degrees Fahrenheit; otherwise they will not cure properly. Barnhill Chimney generally schedules waterproofing treatments in the spring and summer months. Waterproofing does not take long to apply, cures within a week (depending on the brand) and lasts from two to ten years depending on the brand, the chimney, the weather, and other factors. If your masonry chimney is showing early signs of water damage, a prompt waterproofing treatment can help prevent further deterioration and prolong the life of your chimney.

PPK waterproofing applied by Barnhill Chimney Company comes with a 10-year warranty.

Material Data Sheet

A chimney treated with “PPK” breathable waterproofing. Water beads right up!

Apr 192013

Water entry is the primary enemy of masonry structures. Masonry is porous, meaning that water doesn’t just run down the sides of your chimney when it rains — it sinks in, and enters the masonry itself.

Effluorescence on a masonry chimney


Once inside, the water can carry minerals from the inside of the brick to the outside, forming white deposits known as effluorescence (left) on the structure. These deposits are primarily an aesthetic problem, but they are indicative of water moving freely through the structure.

Plants growing on a masonry chimney

Plants growing on a chimney

Moss and other plants (right) can also grow on a chimney which is holding water. Moss is generally just unsightly, but weeds and even young trees can grow as well — breaking apart the bricks with their root systems, attracting birds and animals, or even blocking the flue.

Spalling bricks

Spalling bricks

Water can also freeze inside the masonry. When water freezes, it expands, and when it expands inside the masonry it can damage the structure, cracking bricks and breaking off flakes, or even large portions of bricks, an effect known as spalling (left). Spalling can weaken the structure of a chimney and render it unsound.

Eroded mortar joints

Eroded mortar joints

Water moving in the masonry also erodes the mortar in the joints (right) between the bricks. When this happens, the chimney can become extremely unsound.

Outside Mount Stainless Steel Chimney CapThe best defense against water entry is a full size chimney cap, which covers the entire chimney crown including the corners, and directs water away from the chimney. Such a cap, paired with a breathable masonry sealant applied to the vertical surfaces of the chimney, greatly reduces water entry and can significantly prolong the chimney’s life.


Common Points of Water Entry in Masonry Chimneys