Here’s everything you need to know about brick spalling at security bar embeds
In the historic neighborhoods of Washington DC such as Capitol hill and Dupont circle in Georgetown, it’s common to see examples of brick spalling and deterioration and damage at window and door openings coincident with mounting locations of historic security bars. At the time of the original construction of much of Washington DC neighborhoods, crime wasn’t so bad that security bars were really necessary to keep a house secure. Times have changed again and again throughout the past century and security bars have been installed and then in many cases taken back off and in some cases installed again. That reflects the changing nature of economics and disparities in the community and urban built environment that we live in, here in Washington, DC.
Typical Home Front Facade In Capitol Hill
The picture below shows an example of a typical Capitol Hill row home front facade. This masonry facade was built with historic pressed brick, set in a butter joint of lime rich mortar.
As a side note, you can learn more about pressed brick and the important distinctions between pressed brick and common structural brick, and associated differences in restoration at our past articles:
- Front Lumpers Vs Unskilled Labor In Historic Masonry – Part I
- Front Lumpers And Pressed Brick – Part II
- The Early History Of Bricks
- Brick Bond Types Part II
If you look closely at the brick that borders the perimeter around the openings for the doors and windows throughout the facade of the house, you can see several areas where chunks of the bricks are missing. That is one type of masonry spalling.
These locations are coincident with locations that previously had security bar’s steel mounting rods inserted into the brick. Those areas were cut out with a hand drill or set at the time as the brick was laid and then the steel bars were inserted into the window opening recess and the rest of the remaining frame for the security bar was connected to those inserted embedded steel rods. In modern times, we would use a similar but alternative type of embedded fastener. Instead of Inserting bare steel, we would insert a threaded fastener or wedge anchor. Neither of those types of technologies are necessarily better for the maintenance and preservation of masonry, but they do not oxidize quite as fast, to the extent of historic commonly used ferrous metals. Commonly available historic ferrous metal had lower carbon content and was more on the spectrum of iron than steel. Steel rusts and oxidizes nonetheless, but will, in many cases, be a little bit more resistant to elements than bare iron.
Expanding Steel Causes Bricks to Crack
The picture below shows a different window at the same building. This particular window also has a area where the expanding steel has caused the bricks to crack and in this case the damage is larger and extends to a total of three bricks at the bottom right hand corner.
As a side note, this picture is also interesting because it shows a side-by-side comparison between this house and the neighboring building. You can only see a little bit of the brick at the edge, across the property line of the neighbor’s house, at the left of the picture. Some interesting observations can be made from that little bit of area exposed in the photograph though:
- Both bricks were painted red, both paints have largely deteriorated and flaked away from the face of the building.
- The building to the right is in need of historic brick tuckpointing, aka repailointing to restore and refurbish the deteriorated masonry joints.
- The building to the right was built with a butter joint mortar that was dyed red to be similar to the color of the brick itself.
- The building to the left has already been pointed, but the pointing was applied very sloppily and possibly has been built or restored with the wrong mortar. If a modern cement was used, modern mortars can be detrimental to the longevity of the brick and can cause spalling throughout the front face of the building, similar to the isolated spots shown in the photo of the security bar mounting locations but more extensively throughout the facade.
Damage From Incorrect Mortar Repointing
Although the building in focus today has the damage of these specific bricks and needs to be repointed, it’s much better for this building and this building’s owners that this building has not already been repointed with incorrect mortar. The damage caused by repointing with the incorrect mortar can be extensive and the cost to redo it again could be extremely expensive and painstakingly laborious.
The picture below is up close and in this picture it’s easier to see more of the detail related to the mortar joints. First, you can notice the joints between the bricks which is typical of a pressed brick is very thin, typical of butter joints in historic brick construction. This is particularly common at front facades. Rear facades, in contrast, are not often exposed to view from the public but sometimes at row end houses there will be a side facade where press brick will have been used. Pressed brick was more expensive and more difficult to install, the material cost was multiples of the comparative material costs for common brick. For this reason, common brick was used to build the sides and rear of the majority of rowhomes. And even not all historic row homes were built with pressed brick in historic times because it was more expensive and reserved for the finer buildings of Washington DC. The labor was also not only more expensive but different than the labor used for building the sides in rear walls of historic buildings. In fact the people who built the front facade, at the exposed pressed brick surfaces were entirely different from the people who built the rest of the building. Those people were particularly called “front lumpers”. We recently wrote a two-part article to examine some of the details around the labor breakdown at the time of historic original construction of many of these buildings in Washington DC. You can see those articles, for reference at the following links:
- Front Lumpers Vs Unskilled Labor In Historic Masonry – Part I
- Front Lumpers And Pressed Brick – Part II
How Rusting Metal Can Cause Spalling
To understand how rusting metal can cause spalling, it’s important to understand the expensive force and pressure created by oxidizing metal. The concept sounds very counterintuitive, we perceive and understand bricks to be very strong and we can read the engineering data and see that bricks have a compressive strength that is generally over thousands of pounds per square inch. In total, bricks don’t just appear strong, but they also can be tested and perform in a technical capacity that proves they are very strong and resistant to several types of forces. While all this is true, it’s also important to understand the amount of expansive force applied in a very small area by oxidizing metal. It’s similar to the expansive force created when water freezes and turns to ice. Water molecules, when freezing at 32° F, naturally arrange themselves by following the attraction of their electron bonds and instead of flowing past one another as they would in a normal liquid state they become a less dense, more voluminous solid with a hexagonal molecular framework. This happens because the hydrogen atoms in water molecules which lack a neutron are always trying, in a weak connection, to bond with the hydrogen atoms of other water molecules but the higher temperature makes them instead move and never slow down long enough to stop and form a lattice framework. That all changes at freezing temperatures though because the molecules stop flowing and just vibrate in place, in a way humans cannot perceive by sight and touch alone. This hexagonal, lattice framework is super strong, and less dense, and takes up more voluminous space than the flowing warmer state of liquid water.
Oxiding metals expand in a different but similiar way, and this expansion happens at enormous force which translates to pressure against the brick.
From the perspective of analyzing the brick’s strength, in summary it’s clear that bricks have enormous compressive strength. The term compressive strength, means a brick can withstand the pressure of being smushed between two heavy and hard items or materials. But kiln fired clay bricks and many other types of masonry elements generally lack significant tensile strength. Tensile strength is very different than compressive strength and instead tensile resistance measures not the ability of a material to be smushed but the material’s ability to withstand being stretched or pulled such as without being confined between an additional surface. Bricks and even some of the strongest cementitious building materials such as cast in place concrete do not perform well to withstand compressive forces. And in this case, the expanding oxidizing ferrous metal is applying a tensile force to the brick. Not just any tensile force but a concentrated force: strong and in a small area. The brick cannot withstand this pressure and the bricks will crack and spall.
How To Maintain Your Building
To properly maintain, repair, and care for these historic buildings, a knowledge, interest and understanding of historic building principles is required. Here in Washington DC, historic masonry buildings are extremely expensive and the amount of financial loss caused by improper repointing and low quality construction is staggering. However, in addition to the direct financial value of the property, there is also a cultural loss when historic buildings are damaged. By comparison, consider neighboring poor cities, when historic buildings are damaged, it’s not just the loss of value to the property owner, there’s also a loss to all inhabitants and visitors of a city, present and future, who care about architecture, history, and culture.
We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the historic built environment of Washington DC and neighborhoods such as Capitol Hill, Dupont Circle, and Georgetown and become educated on on the difference between proper historic preservation versus improper work which leads to significant damage to the historic fabric of a building.
From a conservation and preservation perspective, several approaches can be taken to improve conditions related to deteriorated historic brick masonry. Primarily, lime mortar brick joints and low temperature fired soft red clay bricks should be inspected and checked on a routine maintenance schedule, either seasonally or at least annually. If brick masonry is kept in good condition, the life of embedded wood elements can be significantly extended. Hire a professional contractor which specializes, understands and appreciates historic construction elements and buildings.
In this article we talked about the terminology and concepts of historic masonry restoration, follow the links below for more related information from the IDS website:
- Binders in mortars and concrete
- Brick burns
- Butter joint
- Capillary action
- Cantilever
- Cementitious siding
- Cheek wall, masonry — Draft
- Chemical testing
- Code, building — Draft
- Cold joint
- Cold weather masonry work — Draft
- Damp proof course
- Downspout
- Electrical distribution panel — Draft
- Fenestration
- Ferrous metals
- Great Chicago Fire
- Green bricks
- Gutter, roof
- Lime mortar
- Lintel
- Load path
- Oriel window
- Oxidation
- Parapet coping
- Plug, clay
- Pressed bricks
- Raking, of mortar joints
- Raggle, aka reglet
- Rectilinear
- Roman bricks
- Roman arches
- Roof eave
- Roof termination
- Row buildings and row homes
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- Rubbed bricks
- Rubble stone masonry
- Sand, Builder’s
- Sedimentary rock
- Scratch coat
- Sprung arch
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- Squint bricks,
- Strike, or striking of mortar
- Tapestry bricks
- Tooth-in, interlocking masonry connections
- Vitreous
- Water diversion systems
- Zipper-joint
These concepts are part of the fundamentals of historic masonry restoration, tuckpointing, and brick repair.
The links in the list above will take you to other articles with more information on defects, failures, preservation and repair of historic masonry. You can learn a lot more on our blog. Feel free to check it out. If you have questions about the historic masonry of your building in Washington DC, fill out the webform below and drop us a line. We will be in touch if we can help.
