Chicago's brick buildings in peril
Chicago is, mainly, a brick city. Oh, sure, there thousands of wood frame and brick veneer houses and buildings throughout our city, but travel the neighborhoods (Chicago is also a city of neighborhoods, from Lincoln Park to Beverly). Most of this city was built with bricks and mortar. Properly built masonry buildings need very little repair or maintenance but, as these houses age it is obvious there will be needed repairs.
And therein lies the problem.
Seems simple enough, doesn't it? Take out the old stuff and put in some new stuff, or smear some new stuff over the old stuff. The problems come from the "stuff". Most folks don't realize it, but the masonry materials we use in modern construction are completely different, (like, down to a molecular level different), than the materials our masonry homes were built with several decades ago. And, many times, the new "stuff" is not nearly as good as the old stuff was.
Chicago was built with brick. This is, in large part, because of the Great Chicago Fire of 1871. Hundreds were killed and over 4 square miles of the city were completely destroyed. The fire's northward expansion stopped at what has become a famous landmark, the Chicago Water Tower.
And, please notice, the Water Tower is built from masonry.
This building boom lead to the use of what has become known as Chicago Common Brick. Made from very high organic clay (a waste by-product of the construction of the Illinois & Michigan Canal) this brick is very durable. It is also softer and more absorbent than modern brick. It also expanded and contracted with atmospheric changes, so it was necessary to use a softer mortar that had similar expansion characteristics. The mortar that was used in the original construction was lime based, either lime mortar, or a mixture called lime putty.
Lime rich mortar has several characteristics that are completely different than modern Portland Cement, additive laden mortars. As water migrates through lime mortar, some of the lime is disolved and will travel with the water and refill small cracks that occur due to normal settlement (called autogenous healing). Lime mortar will expand and contract to account for movement caused by atmospheric changes. Lime mortars cure by carbonization (from contact with CO2 in the air) rather than by hydration, as modern Portland Cement mortars do. It also was compatible with the moisture permeability of the bricks so water was absorbed and evaporated equally from both materials. The older (solid stone) masonry would also absorb some amount of moisture, but the sheer mass of the wall would limit the amounts of moisture & the depth of penetration, and the moisture will evaporate back out of the wall with atmospheric change.
In the 1930s, Portland Cement mortars were introduced. They are hard, brittle, and moisture resistant. When new Portland Cement mortars are laid over the old original lime mortars, the water resistant mortars act to traps water in the wall. When the walls freeze and thaw in winter, the retained water expands and the walls fracture and fall apart. Building owners see the deterioration occurring, and mistakenly think they need to add more and more Portland cement to "keep the water out". What they are actually doing is keeping the water "in"! Additional repairs with modern mortars accelerate the deterioration of the wall, as each new application seals the wall tighter and tighter. The end result is substantially damaged masonry.
I have, personally, seen 100 year old brick buildings, whose parapet walls were "rebuilt" using the standard Portland Cement mortars available today, where the rebuilt portion has literally disintegrated in 4 to 6 years! Modern masonry techniques are, literally, destroying these old buildings and houses.
Many restoration masons utilize modern Portland cement mortars because they are readily available at the big box stores, they are fast to mix and apply, and most significantly, the masons don't have a clear understanding of what is necessary to perform a proper long lasting repair in the first place. In the end, the less savvy building owner thinks that since the entire wall is clean looking and appears to have been "re-pointed" uniformly, he has received a good and very affordable repair. In fact, what they receive was a cosmetic overlay, which in most cases, accelerates the deterioration of the masonry. Also, with the recent influx of Eastern European masons, their common practices are not proper for the Chicago style of building. They, regularly, add additional sand to the mortar, hoping that this will add strength. In fact, it makes the mortar mixture more water permiable. This allows more water to be retained by the building's brick.
The most common result of improper mortar application is that the thin layer of parge mortar cracks & falls off within a few years. In the areas where the new mortar extends deep enough to remain in place, moisture tends to be trapped in both the mortar bed joints and the edge surfaces of the brick. This causes the moisture laden brick to deteriorate through the expansion that occurs as it freezes. This condition is called spalling. Entire faces of brick can literally begin to progressively flake off. In many cases, the trapped moisture will cause entire sections of brick to bulge out away from the building due to freeze/thaw cycles. In both cases, the result is substantially damaged masonry.
And, as icing on the cake, the winter of 2008 - 2009 had a record number of freeze/thaw cycles, and 2008 saw record rainfall levels. Talk about a perfect storm!
The other large problem with old masonry is the steel lintels over the windows and doors. Over the years, moisture migrates into the wall, where it attacks the steel and causes it to rust and delaminate. When the steel delaminates, it flakes and expands, very slowly, but with thousands of pounds of force. The expanding steel causes the brick around the windows to bulge, and causes decorative stonework to crack. The most common (and mistaken) repair is to caulk or grout the spaces between the lintels and the masonry and seal the lintels, which the repairman thinks will keep water out of the wall. What is actually happening is that the water is being retained in the wall, and the lintels deteriorate faster.
Another common problem with the lintels is the relatively recent practice of wrapping the window trim and steel lintels with aluminum cladding when windows are replaced. The intent is to protect the lintels, but the aluminum wrap cladding actually holds the water in the wall, which accelerates the deteriorioration of the lintel.
These misbegotten repair practices are so ingrained in Chicago construction trades, it has become standard practice to keep applying new mortars over the old mortars until there is a convex bulging mortar joint instead of a nicely struck concave joint. There are some new masons that have labeled this "European Tuckpointing", as if the practice has some centuries old roots going back to the "olde" country. While the new masons understanding of American marketing is admirable, the practice is a disaster for the buildings because the bulging joint has thousands of little ledges and gaps that trap moisture and actually funnel increased amounts of moisture into the wall.
There are a couple simple lessons in all of this.
First, it is not necessary to "protect" the older mortars. If we don't actively abuse our buildings by applying the wrong principles, materials, and methods, they will last. They have withstood thousands of years of use all over the world, and if the building is reasonably maintained, tuckpointing is most likely only necessary every 25-30 years at most. Yes, there might be miscellaneous spot repairs necessary, or the building owner might want to clean the masonry to make it look better, but plainly and simply, the original mortars will function just fine for decades if they are not slathered with Portland cements, or otherwise abused by not maintaining roofing, parapet wall coping tiles or other waterproofing components of the building.
Second, if one is doing repairs to their masonry building, they should be aware that there are vast differences in the mortar, and using the wrong mortar is detrimental to the building. When talking to your repair mason, make sure they understand these things. If they don't, the likelihood is they are going to damage your building, not repair it.
Which finally brings us to tuckpointing. This is a commonly misused term.
The correct term for this repair work is "repointing", or simply "pointing". What this means to us is even the terms that the new generation of masons not only use the wrong mortars, they don't even use the proper terminology for their work. Call me old fashioned, but if someone doesn't even know the correct terminology for the processes they employ, I tend to be weary of their knowledge and skill for executing the work.
We are blessed with a very unique architecture and building material in this City. If we want our masonry homes to continue on, we must educate ourselves, and then the tradesman that work on our properties. If we don't do these things, we can expect that our homes will fall apart rapidly and have excessive repair costs. It's always cheaper to do things right the first time.
And, a professional and knowledgable home inspector can help in this regard. Much of my work is consulting, both to home and building owners and to contractors.