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A masonry chimney is constructed of a variety of masonry and metal
materials, including brick, mortar, tile, steel and cast iron.
All of these materials will suffer accelerated deterioration as
a result of prolonged contact with water. Masonry materials deteriorate
quickly when exposed to the freeze/thaw process in which moisture
that has penetrated the materials periodically freezes and expands,
causing undue stress. Water in the chimney also causes rust in
steel and cast iron, weakening or destroying the metal parts.
Water penetration can cause interior and exterior damage to you
home and masonry chimney including:
- Deteriorated metal or masonry firebox assemblies
- Rusted damper assemblies
- Rotted adjacent wood and ruined wall coverings
- Deteriorated central heating system
- Decayed mortar
- Spalled and broken brickwork
- Cracked flue liner systems
The following are the four main ways to prevent water damage.
Install a chimney cap
Chimney caps, also called rain covers, are probably the most inexpensive
preventive measure that a homeowner can employ to prevent water
penetration and damage to the chimney. Chimneys have one or more
large openings (flues) at the top that collect rain water and
funnel it directly to the chimney interior. A strong, well designed
cap not only keeps this water out, but will also prevent birds
and animals from entering and nesting in the chimney. Caps also
function as spark arrestors, preventing sparks from landing on
the roof or other nearby combustible material.
Repair or replace a damaged chimney crown
The chimney crown, also referred to as the chimney wash, is the
top element of a masonry chimney. It covers and seals the top
of the chimney from the flue liners to the chimney edge. Most
masonry chimneys are built with an inadequate crown constructed
from common mortar mix, the same mixture used to lay the bricks
of the chimney. This mortar is not designed for and will not withstand
years of weather abuse without cracking, chipping or deteriorating;
situations that allow water to penetrate the chimney. In fact,
most sand and mortar crowns crack almost immediately after installation because of
shrinkage. A proper chimney crown should be constructed of a portland
cement based mixture and cast or formed so it provides an overhang,
or drip edge, projecting beyond all sides of the chimney by a
minimum of two inches. This drip edge directs the runoff from
the crown away from the sides of the chimney, helping prevent
erosion of the brick and mortar in the chimney's vertical surfaces.
There are also some modern waterproof, non-shrinking, cement like
coatings for repairing damaged mortar crowns that seem to work
fine.
Repair or replace flashing
Flashing is the seal between the roofing material and the chimney.
Flashing prevents rain water from running down the chimney into
living spaces where it can damage ceilings or walls, or cause
rot in rafters, joists, or other structural elements. The most
effective flashing is made up of two elements, the flashing and
the counter- flashing. The base flashing is an L shaped piece
of metal extending up the chimney side and under the roofing shingles.
The counter flashing, which overlaps the base flashing, is imbedded
and sealed in the chimney's masonry joints. This two element flashing
allows both the roof and the chimney to expand or contract at
their own rates without breaking the waterproof seal in either
area.
Waterproof your chimney
Most masonry materials are porous and will absorb large amounts
of water. Common brick is like a sponge, absorbing water and wicking
moisture to the chimney interior. Defective mortar joints or the
use of improper mortar or brick can greatly increase the tendency
to absorb and convey water to the interior of the masonry chimney
structure. Several products have been developed specifically for
use as waterproofing agents on masonry chimneys. These formulas
are vapor permeable which means that they allow the chimney to
breathe out, but not in. Thus water that has penetrated the chimney,
or moisture that has originated from inside, is allowed to escape,
while the waterproofing agent prevents water from entering from
the outside. Paint, or any non vapor permeable water sealer, should
never be used as a waterproofing agent because it will trap moisture
inside the chimney, accelerating deterioration.
Conclusion
Water damage to masonry chimneys is usually a slow, subtle process.
The problem is often not evident until it has become quite serious.
Although these water prevention measures may cost a few dollars
initially, they will save you the major expense of large masonry
repairs or rebuilding of the entire chimney in the not too distant
future, and as such represent a wise investment in your home.
Common signs that show interior moisture problems are:
- Water leaking out of the bottom of the chimney at the clean out
door in the basement.
- Brick at the base of the chimney in the basement are often wet
or dark looking.
- White chalk-like stain of the exterior brick or mortar (efflorescence)
- Brownish stain oozing from brick and mortar in attic
- Chimney in attic is wet during cold winter months
- Brick and mortar above roof line are failing
Please Take Note: If you do have damage check with your insurer because in some
cases your chimney and masonry clay lining repairs may be covered
by home owner's insurance.
Call Jen-Chris for expert advice and professional installation of all your chimney
materials.
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