Dampness on Chimney

Old 01-01-00, 11:22 AM
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There is a wet place on the outside of my chimney. It starts approximately two feet from the base and is on the exterior. It also seems to start at the mortar seam.

Should I be concerned and if so what can I do?
Old 01-02-00, 03:17 AM
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Leaks though masonry joints are not a good sign. Over time other problems can manifest.
Before going off the deep end, know that the problem may either be a minor one or it could be an indication of more serious damage to come.

A masonary fireplace and chimney are constructed from a number of dissimilar materails. Excluding the by products of combusion and their corrosive effects, the main points of moisture penatration will be at the juncture of materials. Masonary products are porous. Warm moist air from an attic can penetrate the brick, grow cold, fall, and the next morning the chimney will sweat as the mositure escapes. By the same token, moisture from a ground source will have a similar affect. Moisture and Sulfer Dioxide, by products of combustion, can play rolls also. When the two combine they form Sufuric Acid, which in turn errodes brick and mortar.

Examine the chimney from the outside and inside, from top to bottom, or hire it done.
Is the chimney leaning(?), if so: at the top or bottom?
Top: generally a sign of advanced errosion. This can result from near by industry exhausting Sulfer Dioxide, or from a poor maintence practices.
Bottom: foundation and/or soil problem.

Check to see the that the ground slopes away from the chimney.

Using binoculars or a spy glass, examine the brick and mortar.
Vertical mortar joints often fail before horizontal joints. Look for signs of cracked brick. Pay attention to changes in plane surfaces and to caulking, if it exists. Check for contibuting causes, such as gutters and downspouts.
Repoint and repair when the temperature allows. From the roof examine the crown, cap, flue, and flashing.
The concrete or stone crown should extend over the edge of the brick work, and there should be a break joint seal of caulking between it and the chimney flue. An erroded or a missing cap (sits over the flue) should be replaced. The flue should extend above the crown. Remove the cap and with a strong flashlight look down the flue for evidence of cracking. If it's dirty have it cleaned. Minor cracks in the flue can sometimes be filled, but at some point replacement will be necessary. Have errored or damaged flashing replaced. Copper and lead are better than galvanized.

From the attic examine the brick and mortar, looking for the same signs as on the exterior.

From the firebox and with old clothes a glove and rag, reach up through the damper and back down to the smoke shelf. Creosote and acid build up here. Left for long periods it can errode brick and mortar. Is the grout spongy? Have it tended to.

Check the firebox for cracks. Most can be repaired with "fire clay" from a "caulking tube".

Anything else, call a pro.


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