Sign up to receive information about upcoming
articles and other information
about Traditional
Masonry.
Traditional Masons Practice Healing Arts on
Fireplaces &
Chimneys
by Chris Mayo A log home in a historic ravian German village presents a veteran restorer with a terra cotta challenge.
Nobody has declared an official “flue epidemic,” but an increasing number of masons are finding themselves called in to help heal traditional fireplaces and chimneys.
While many brick or stone-built fireplaces and chimneys endure for hundreds of years, others develop “ailments.” Discerning the difference between cause and symptom is not always easy for those involved in traditional masonry.
Often, symptoms point to deeper issues. Cracking, for instance, may indicate faulty construction, post-construction settlement, or stress due to remodeling. Other problems may be traced to carelessness or neglect, such as a failed crown that allows water to drain into the chimney. Poor design coupled with lack of sweeping and inspection may cause masonry to decay from within. Some failures can be traced to previous repairs with incompatible materials.
Regardless of the ailment, it is up to the traditional mason to set things right again. Whether brick or stone chimneys and fireplaces are in need of minor repairs or complete reconstruction, traditional masons can diagnose problems and prescribe correct treatments.
Traditional masons find themselves busy fixing masonry fireplaces even despite the growing popularity of prefab fireplaces. While prefabs are less expensive to buy and install and they broadcast heat well, few within the industry expect them to have the endurance, look, feel and prestige of traditional masonry.
Moreover, homeowners who wish to preserve the original look and integrity of their homes — be it for aesthetic reasons or to maintain a historic designation — are increasingly turning to highly trained masons to work on their fireplaces.
Ernest Bingham, master chimney builder for Wisconsin-based Great American Chimney & Masonry, is one of those masons. “Think of the fireplace and chimney as three separate components: above the roof, below the roof, and the unit’s dynamic internal parts,” he says. “The outside, above the roof, is disposable and normally breaks down from the inside out. When used up, it can be rebuilt with relative ease every 50 or 75 years.”
A joint effort
Traditional masons performing joint work — above or below the roof line — must chose replacement mortar with care, says Ben Hurd, owner of Missouri Stove & Chimney LLC, who specializes in the restoration of traditional stone chimneys attached to log houses. Choosing a mortar with the proper color and hardness is key.
“We like to use as close to the traditional mortar as we can find,” Hurd says. “There are several ways to deal with that. Lime putty is one way. Some people use hydraulic lime. For most work, it depends on how particular the customer or architect is. Type O mortar with the correct sand to match color performs reasonably well and is a pretty good mix.”
To avoid applying a remedy that is worse than the disease, masons working on traditional chimneys and fireplaces normally avoid gray type N or type S mortar. Beyond being aesthetically unpleasing, mismatched mortar may cause adjacent units to fail. Mortar that is too hard may expand and contract at rates different than those of the surrounding units, causing damage or inviting moisture-related problems.
“Grout [mortar] harder than the substrate will drive moisture to the stone or brick,” Hurd says. “You can create damage that way. Generally speaking, soft stone or soft brick is very susceptible to this problem.”
Fireplace interiors are dynamic in nature and must be able to withstand extreme temperature leaps in a moment’s time.
“The inside from bottom to top is dynamic,” says Bingham. “Fireplaces and chimneys have to perform in extreme temperatures of up to 1,650 degrees and with ember beds from 1,000 degrees to 1,500 degrees. Dynamic components typically last 35 to 75 years at a pop, but you can fix absolutely everything in the interior dynamic component independent of the static components.”
Bingham does not advocate tuck-pointing brick chimneys above the roof line. Beyond repointing work, typical dynamic component repairs include tile replacement, loose brick replacement, damper repair or replacement, and crack repair.
Treat cause, not symptom
Especially when dealing with cracks, savvy traditional masons always make sure to look for causes underlying the symptoms.
“Damage to the hearth and fireplace surround can often be traced to builders not understanding how fireplaces work,” says Bingham. “Where we find exteriors damaged is often where they link the outside static components to the inside dynamic components. An example is a mason who might not realize that parts move when they get hot. He might infill the areas from the smoke chamber to the flue because it’s easier to do that than to dispose of extra mortar. Inherently when you see structural damage from floor to ceiling level, you’ve got to suspect the dynamic has been sewn to the static.”
Most problems caused by dynamic-static links can be undone by removing the bonds that tie them.
“You can fix absolutely everything in the interior dynamic component independent of bottom or top outside stack — and vice versa,” says Bingham. “They are not one static lump that you have to cut into.”
Lost art
At some point, restoration artisans will be asked to rehabilitate chimneys from the 1950s. They should know that chimneys built in the latter half of the 20th century don’t always perform as well over time as older chimneys, and there are reasons for that.
“When I began the trade, it was under an old Norwegian classically trained in fireplace construction,” says Bingham. “He put it into me that the lore of the trade goes back 12,000 years and he had supporting data to back that up. But new construction no longer has a place for that kind of skill.”
According to Bingham, changes in construction methodologies slowly led to devolution in chimney and fireplace design in America.
“Deep training in a narrow field became superfluous to new home construction,” Bingham says. “The lore of fireplace building really fell through the floor, and 99 percent of the fireplaces were built by the same bricklayer who built the front porch.”
The 1930s witnessed a slow dropping off, but traditional chimney and fireplace craftsmanship seemed to screech to a halt in the 1950s. Why? To satisfy a post-war housing boom, the typical home-building team morphed to completely exclude the fireplace mason.
Unbeknownst to those not deeply steeped in the art of fireplace design, subtle and inadvertent changes in construction began to create problems that would not surface for years, or decades, to come.
Fireplaces constructed in the later half of the 20th century by masons not trained in fireplace and chimney work often looked nice and performed reasonably well. But subtle changes begat subtle problems. Fireplaces began to lose their round or parabolic interiors. Bingham believes part of this transition can be traced to the easy availability of prefabricated cast-iron dampers, which hinder the upward travel of heat and smoke.
“A damper is a good idea when it’s round, but not square,” Bingham says. “Gas wants to rise in a counterclockwise spiral. But a square damper breaks up the spiral into a whole bunch of spirals.”
Once these spirals pass the damper, the smoke has back pressure and has to work harder to exit the flue. Couple that with nonrounded areas — such as corners in smoke chambers and flues — and
you’ve got the anatomy of a failure, according to Bingham.
“A lot of smoke chambers are square with hard edges,” he says. “Chimneys without rounded edges have cool spots and corners where creosote collects.”
Creosote is considered by many to be a fireplace and chimney’s worst enemy. A natural residue of burning wood, especially green wood, highly acidic creosote is deposited on the inside of fireplaces and chimneys. If left to linger on fireplace and chimney surfaces for prolonged periods of time, acids in creosote literally eat through mortar.
“When you build a fire out of solid fuel, you create a chain of acids and hydrocarbon exhaust that lines the chimneys,” says Bingham. “The chimneys are alkaline in nature, the mortars and brick are alkaline. Eventually, the crystalline structure of the acids attacks the binding agents of the mortar and bricks. Without periodic sweeping, the chimneys begin to break down — they dissolve from the inside out.”
Proceed with caution
Such crumbling chimneys, though they may look basically solid above the roof, are typically not good candidates for repointing. Rather, they may require extensive surgery.
Typically, trained chimney and fireplace masons will chip away at the hardened, outside layer of mortar, notice the deterioration, and tell his or her client. Untrained or unethical masons may be tempted to apply a band-aid treatment — often to the long-term disadvantage of the owner.
The traditional chimneys and fireplaces worked on by Hurd of Missouri Stove & Chimney rarely exhibit the significant internal damage of which Bingham speaks.
“It’s hard to beat a 200-year-old masonry chimney that’s 8 inches thick,” says Hurd. “Even if you have a partial failure or a problem requiring repointing, you always have quite a bit of material there.”
To illustrate the vast differences in the construction of chimneys and fireplaces throughout the continent, Hurd shares a surprise he sometimes finds during examination of joints.
“Most repointing is pretty basic,” Hurd says. “You need to remove a sufficient amount of the old mortar. A rule of thumb is to remove up to two times the width of the mortar joint. So in a traditional stone chimney, where an inch of mortar is typical, you might go a couple inches deep. But when you get into some of these old chimneys, there might not be mortar more than an inch or so deep. You find clay or mud.”
But mud or clay in lieu of mortar is not necessarily a bad thing, according to Hurd. A lot of old chimneys were constructed with mud or clay as the interior mortar. And clearly, they last the test of time.
“It may sound crude to a lot of people, but I’ve gone into many chimneys where they’ve been plastered with mud, and they’ve been there for 200 years,” Hurd says, noting that many such structures were erected dry-stack. “If you chip at it with a hammer or chisel you’re going to knock it off, but it’s been there for a long, long time, doing its job.”
In the 1700s, an American inspires a fireplace revolution
Pinpointing when our early ancestors built the first fireplace and chimney is not as simple as circling a date on the calendar. While many believe fireplaces and chimneys evolved tens of thousands of years ago as mankind sought to bring fire indoors, others feel the modern iteration dates back only a few hundred years.
However, most historians agree that an American living in Europe greatly helped fireplaces and chimneys evolve.
Dubbed Count Rumford by the Bavarian government, Massachusetts-born Benjamin Thompson is famous for both his work on the nature of heat and his invention of a revolutionary new fireplace.
The Rumford fireplace was smaller and shallower than conventional fireplaces of the era. Their covings were angled more to radiate heat better. Rumford also streamlined the fireplace’s transition between fire-box, smoke chamber and flue.
“When the breast of the chimney is properly rounded off, the ascending cloud of dust and smoke more easily finds its way into the throat of the chimney, and is even directed and assisted in some measure by the warm air of the room that gets under the mantle, and is going the same way,” Rumford wrote in “Essay IV: Of Chimney Fireplaces,” first published in 1796.
Rumford reasoned that by removing all hindrances, smoke would follow its natural tendency to rise up the chimney. Sure enough, Rumford chimneys prevented smoking, saved fuel and produced more heat. Soon, the Rumford style was in vogue on both sides of the Atlantic Ocean. Rumford fireplaces and chimneys built of stone and brick began cropping up throughout the North American continent.
Why some old chimneys get the bends by Richard O. Byrne
There is an important piece of chimney pathology that many restoration workers ought to understand.
Most older chimneys were laid up using lime as the binding agent in the mortar, i.e., calcium carbonate. Inside chimneys, as flue gases pass through the roof line, they become cooled in the cooler temperatures above the roof, and a weak sulfuric acid is produced and deposits on the insides of the chimney as a condensate. The acid in turn attacks the lime and changes it from calcium carbonate — lime — to calcium sulfate, i.e. gypsum.
And since gypsum takes up more room than the lime did, the mortar beds in the chimney widen. One can notice this effect on some chimneys when they bend away from the wind. It is not because the wind has forced them over. It is because the windward side is the coolest, and the greatest amount of acid condensate is deposited there, producing more gypsum, which in turn causes the joints on that side to expand more and bend the chimney. (I have a picture showing 15 or so chimneys in New Bedford, Mass., all bent this way, and it is a common site in old seaports.)
It is the rapid cooling of flue gases and the resultant formation of sulfuric acid condensate above the roof line that is the main reason for the marked difference in damage to the chimney between the attic and the open air above it. Most masons don’t know this, yet it is vital to the understanding of the pathology of the chimney’s materials.
One should also mention the damage caused by chimney fires within ceramic and metal flue liners. Metal liners that have suffered a flue fire are badly distorted and may be unsafe for future use. Ceramic flues can be totally destroyed from the intense heat and resultant cracking. Keeping chimneys free of creosote is a must. A wise man ensures there is rapid and safe access to his chimney flue from its top. A good chimney fire sounds like the roar of a freight train going by.
If enough flue trash falls down the inside of a chimney, the chimney can become plugged solid and the inhabitants of the house killed from carbon monoxide poisoning.
One should also mention that in older brick and stone homes, areas where the chimney comes in contact with wooden elements such as joists and floorboards should be inspected with great care, as it is here where ignition can occur if the pointing is no longer sound within the chimney.
Traditional Masons Practice Healing Arts on
Fireplaces &
Chimneys 
