By Stuart Karanovich and John Meredith


“When I was a young man I had a very good friend who owned a service station. One evening after a night out he confided in me that while he loved what he was doing, he was going broke and would probably soon be forced to sell. He knew that I had some business experience and asked if I would be willing to come by, take a look at his operation, and see if I could come up with some recommendations which might help him. Back in those days there was an attendant who pumped the gas. The problem was that was all he was doing. I suggested that they start looking at the WHOLE car, from the tires, to the belts, oil levels, hoses and wiper blades. Soon, cars coming in for gas were leaving with gas AND these needed repairs. My friend’s business quickly got back on sound financial footing and his customers raved about his service, all because they stopped doing just the obvious and started treating the whole car as a system.” — Stuart

I tell you this story because I see the same thing happening in our industry as it relates to water intrusion.

We go out to clean a chimney and while we’re there we notice the chimney doesn’t have a cap, the crown is cracked, or the flashing is missing, and we correct it.

We did the obvious, but we didn’t treat the chimney as a system. In other words, we pumped the gas! And when we did, we may or may not have fixed our customers problem.

Don’t misunderstand me, I’m not opposed to fixing the obvious problems that you encounter in the field. What I am suggesting is that you look at water penetration through the lens of the chimney as a whole, see it as a system. You will provide a better service to your customers, eliminate unpaid call backs, and increase your profits.

Most experts agree that the durability of external masonry chimneys depends primarily on its resistance to water penetration.

Water damage may include corrosion, deterioration, dimensional damage, efflorescence, freeze-thaw spalling, staining, damage to interior finishes and ultimately, structure failure.

Chimney design, material selection, and quality of construction are the most important factors in determining the ability of a masonry chimney to resist water penetration. Proper construction practices are beyond the scope of this article. Instead we will concentrate on understanding the causes and mechanisms of water penetration in an effort to better diagnose and solve these problems before severe damage occurs.


The main source of masonry water intrusion is driving rain, which is most evident at the corners and top of a chimney system because of changes in air flow patterns at these locations. When masonry chimneys are exposed to driving rains for several hours they will usually reach their saturation point. Depending on conditions, saturated walls can take from one to several days to shed most of this water.

Trees, plants, and micro-organisms like algae, prevent it from drying, which often leads to leaks and/or damage to the chimney structure.

Mortar Joints

This is often complicated by the use of other than type N mortar as recommended by the Brick Institute of America (BIA) for above grade exterior structures such a chimneys. Proper tooling of the joints will also affect the chimneys ability to withstand water intrusion. The BIA recommends that only concave, v-shaped or compacted grapevine mortar joints be used for exterior masonry because these methods compress the mortar to achieve a better bond with the brick. Weathered joints are also recognized as acceptable for exterior use. None of these joints don’t tend to collect water and therefore provide better rain resistance than flush, struck, raked, or extruded joints, which are acceptable for interior applications.

Condensation Problems

Water damage can also be caused by condensation within the chimney system itself. Chimney systems are especially vulnerable to condensation because water vapor is a large component of flue gasses. Most of the water vapor escapes out of the flue, but some will pass through tile liners and mortar joints between the liners, especially if they are cracked, deteriorated or missing.

The greatest exposure to condensation occurs during the heating season as surface wetting and use of the system produce high humidity in the air cavities surrounding the liners. When the temperature of the outer chimney wall falls below the temperature in the air cavity, condensation often occurs on the inside walls. Independent testing has determined that each masonry unit is capable of absorbing up to 1/2 lb of water from condensation.

Stress Cracks & Volume Changes

Stress cracks and volume changes in the masonry can also be responsible for water penetration. Stress cracking may be caused by movements in the foundation, structural frames, wood expansion, vibrations and fire. Volume changes can be caused by temperature, moisture, water or salt crystallization, or corrosion of embedded metal. Water can enter a chimney system through these cracks where it accumulates until it either penetrates to the interior, drains to flashings where it is redirected through weep holes, or simply evaporates.

Masonry Absorption

Although masonry is relatively dense, it is also a porous material composed of a network of interconnected pores called capillaries. These capillaries circulate water by means of suction. Capillary suction is an important factor for openings smaller than .01 mm, while hairline cracks can range from between 0.0 mm to 1 mm in width.

Chimney Flashings

According to the Brick Industry Association, without flashing a chimney system, any intersection or interruption of materials becomes an avenue for moisture to enter the system. They recommend flashing at three primary areas: the base of the chimney, the intersection of the chimney and the roof, and at the chimney crown.

The base of the chimney is constructed in much the same manner as a brick cavity wall. Flashing should be used at the juncture of the foundation and the brickwork. The flashing should extend through the exterior wall and turn up behind the exterior face of the brick.

Where the chimney system passes through the roof, base and counter flashing should be installed. The base flashing should extend a minimum of four inches along the roof and four inches up the chimney face, with tabs at all corners. The counter flashing should be lapped over the base flashing a minimum of three inches. It should extend through the chimney wall and be bent upwards into the air space between the chimney and flue tile. All joints in the counter and base flashing should be completely sealed.

Flashing the chimney crown is often overlooked when looking at water penetration. The BIA recommends that the flashing be placed directly below the crown, extending through the chimney and either inserted into a gap between the tiles or up over the top flue tile and bent over the top of the flue opening. Using this method of flashing does not negate the need for the use of sealant at the juncture of the flue liner and chimney crown.

Chimney Crowns

Most of the crowns that we encounter are either improperly designed or failing, and a prime source for water to penetrate the chimney system. Poor crown construction is one of the leading causes of chimney deterioration. According to the BIA, crowns should be constructed of concrete, not mortar, they should also be two inches thick at the thinnest portion, slope downward from the flue liner, and extend over the edge of the chimney at least two-and-a-half inches in all directions. They should also have a drip edge no closer than one inch from the wall of the chimney and there should be a bond break between the crown and the flue to allow for expansion and contraction.

I have attempted to cover the most common sources for water penetration in masonry chimneys, but this list is far from complete. I am sure that some of you have encountered water penetration problems that seemed to defy logic, or at the very least was not an intuitive find.

The Chimney Problem Checklist

John Meredith, CEO and founder of SaverSystems, recognized many years ago the need to treat water permeance in masonry chimneys as a system and developed the Chimney Problem Checklist to assist in doing so.

Using the Chimney Problem Checklist and its over 30 points of inspection for each chimney, a technician will be able to accurately determine all possible causes of water intrusion into the chimney system. Armed with that knowledge, you will be able to confidently determine the methods that need to be undertaken to satisfactorily recondition the chimney system.

Working from the Chimney Problem Checklist, the homeowner can then be presented with a proposal that addresses all deficiencies observed during the inspection. Let’s say that we observed small cracks in the crown, water being readily absorbed on the face of the chimney, and a missing (but required) cricket. Our proposal would be written, listing each repair and its cost.

We would also include a separate line item for a discount if the customer opted to have all repairs completed. Our proposal would also state that for us to warrant our water remediation, all repairs suggested would need to be completed.

If our customer decided to have only the crown repaired and a water repellent applied to the face of the chimney and to defer having a cricket installed, then acceptance of our proposal would carry the understanding that if they continued to have water penetration issues and we had to return to correct them, it would not be warranty work, eliminating an unpaid call back.

An important point to be aware of, is that water penetration in a chimney system can often be caused by several conditions. Each condition by itself may not be enough to overwhelm the system, but when taken together do, allowing water where it should not be.

If a customer chooses to correct some, but not all of the conditions you have uncovered during your inspection, water penetration may stop for a period of time, only to reappear when the defect(s) not corrected deteriorate further, and are then able to overwhelm the system, allowing water to penetrate. In those cases, revisiting your original proposal and educating the homeowner will avoid unpaid warranty work.

Through the use of The Chimney Problem Checklist, and by viewing water penetration issues in masonry chimneys as a system, you will solve more of your customers’ problems the first time, maximizing their satisfaction, and your profitability.

Note: This article originally appeared in the May issue of Sweeping magazine, the monthly magazine provided to members of the National Chimney Sweep Guild. 

Next steps: Contact the CSIA Certified Chimney Sweep in your area. This person, certified through the Chimney Safety Institute of America, may be able to help! Use our free zip-code finder at