The dark streaks on this chimney are mold growths, indicating water penetration. Mold and moss growths will weaken the mortar joints of a masonry structure.
The mortar wash at the top of the chimney and the ledge created by the stepped in bricks are common construction defects that lead to water penetration problems.
This chimney previously had a concrete slab over top of it, supported by brick pillars. The slab was removed to allow installation of a stainless steel liner for the wood stove.
The terra cotta flue tiles have been damaged by a flue fire sometime in the past. Gaps and cracks in flue liners allow flue gases to escape the liner, condensing as creosote in the rubble outside the flue. Note how the interior of the chimney around the flue tile has been darkened by creosote accumulation.
After a little work, the mortar wash and top two courses of brick have been removed. We arranged rubble to fill the cavity and provide a mostly level surface to support the concrete crown.
Plastic sheeting provides a bond break between the concrete and the chimney structure. Foam insulation wrapped around the flue tile will form an expansion joint to allow the flue tile to expand when heated without damaging the crown.
The plastic sheeting covers the whole top of the chimney and part of the form bottom. The crown will be completely isolated from the chimney structure.
When the surface water has mostly evaporated, we trowel a smooth surface on the concrete and use an edging tool to compress the edges, making them less likely to chip or break.
We put the chimney cap back in place and the crown is complete. The crown slopes away from the flue tiles to the edge and will shed water nicely. The drip edge on the crown will cause water to drip to the roof or ground, rather than running down the chimney exterior.
It looks pretty nice from the ground, as well. ChimneySaver Water Repellent has been applied to the chimney exterior to minimize water penetration of the bricks and mortar joints.
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Among the myths that abound regarding chimneys is the notion that a masonry structure is waterproof. While it is true that bricks and mortar are sturdy and durable when properly put together, they are also susceptible to damage from water penetration.
Bricks and mortar readily absorb water, but release it more slowly. Over time, water washes away elements of the mortar, weakening it. Mold, moss and other vegetation grows on damp brick and mortar, their tiny root systems tearing at the mortar joints. Water freezes and thaws inside the mortar joints and bricks, causing cracks to widen and brick surfaces to spall. Eventually crevices in the mortar are large enough to catch seeds carried by the wind or birds. The larger root systems of these plants damage the masonry structure more rapidly.
In Upstate South Carolina, water damage is visible on most masonry structures after only a few years. Chimneys are particularly susceptible to water damage as they are exposed to the wind and weather above the roof. Water damage is slow, but it will inevitably destroy your masonry chimney from the top down.
Proper construction and maintenance of masonry structures can prevent water damage. Regular chimney inspections can alert you to problems in your chimney system and give you time to correct them before they become serious and expensive problems.
Click on the images above to see how we correct the common chimney defects that lead to water damage.
