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If
you've ever enjoyed a glass of iced tea on a hot summer day, you've
experienced this "condensation" first-hand. Moisture collects
on the glass when water vapor in warm, moist air condenses on the cold
surface. Something similar could happen in your chimney. Warm, moist
air hits the cold chimney wall and water droplets form on the inside
of your chimney. Condensation was not a problem with your older, less
efficient furnace because more heat escaped up the chimney. According
to nature, these hotter vent gases could carry more moisture straight
out your chimney.
Not so with modern furnaces and their lower emission temperatures.
Moisture can seep into cracks in the bricks and mortar. In cold climates,
the moisture freezes and thaws, and can cause chunks of tile and chimney
to break loose. In the worst-case scenario, this debris could actually
block the venting system, causing a potentially harmful situation.
When not vented properly, excess moisture damage may not be limited
to your chimney. Water could even drip back into your furnace, causing
it to corrode. As it seeps through porous mortar joints, this moisture
could also ruin neighboring drywall.
Water Damage and Your Masonry Chimney
As odd as it may seem, water causes more damage to masonry chimneys
than fire. Think about it for a moment. All the brick and other materials
that make up your home are protected by the roof and eave, all that
is, except your chimney. The chimney bravely sticks up above the roof
constantly exposed to all the elements; rain, snow, and freeze/thaw
cycles.
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 & exterior damage to your home and
chimney including: |
- Spalled and broken brickwork
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- Deteriorated metal or masonry firebox assemblies
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- Rotted adjacent wood and ruined wall coverings
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- Deteriorated central heating system
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- Cracked flue liner systems
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Preventing Water Damage
| Install a Chimney
Cap |
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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.
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| Repair or Replace a Damaged Chimney
Crown |
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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.
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| Repair or Replace Flashing |
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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 base
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.
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| Waterproof Your Chimney |
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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.
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Reprinted with permission from the Chimney Safety
Institute of America, www.csia.org |