Take a close look at front lumpers vs unskilled labor in historic masonry
We often talk about the distinction in historic masonry between the historic common brick vs. the historic pressed bricks. Many buildings use both bricks, but not all buildings were built with any pressed bricks. In fact, many buildings in the historic neighborhoods of Washington, DC were built just with common brick. Both types of brick are equally historic yet they have significant differences. The historic press bricks were used at the front and at the exterior sides of buildings. In rowhome construction, only end units have exterior sides. Also, as a further clarification, the rear ells of historic buildings were generally built with common brick, even in the highest architecturally elaborate buildings in Washington, DC. However, once in a while we might see a circumstance, at the end of a row of buildings, where pressed brick is used on the side facade as well, but it’s relatively rare. Press bricks cost significantly more than the more typical common brick. Common bricks by comparison were comparatively inexpensive.
Common bricks were molded by hand and set into massive yards to lay and dry in the sun. Once the common bricks were dry, they were restacked, then they were fired in large cake beehive kilns or small scale site kilns. Much of the process for manufacturing press bricks was similar. One of the biggest differences though is that with press bricks, the substrate plug or clay used in the mold was sifted to a much higher degree to have significant consistency between these substrate materials used inside of the brick.
That level of sifting and consistency of substrate materials was not found with the common historic bricks. In most cases common historic bricks were created and then laid and set in walls which were planned to be covered with plaster. Currently, in contemporary times, it’s considered aesthetically interesting to have a rough looking brick wall, but at the time, painted plaster was regarded as being more beautiful and more fine for interior space than exposed raw rough brick.
Some of the main differences follow between pressed and common brick:
- Substrate material consistency
- Firing temperature and duration
- Ratio of lime to mortar
- Finer tolerances in setting
All of these four differences, listed above, explain the differences in the physical materials and processes related to creating and assembling those materials. However, one of the biggest differences of all, particularly in contrast with modern methodologies, is that the tradespeople used and employed for the two types of decribed brick construction were entirely different.
In contemporary and modern times, there are still significant differences between different types of brick masons, but these differences are drawn between different lines, due to technological advances in the masonry industry. Many people outside of the industry believe that there’s just one type of brick mason who is simply a brick mason without any differentiation or specialities between one brick mason and another, but that’s not actually accurate. There are different types of distinct classifications of masonry, even in today’s industry. The biggest distinction that we encounter every day, in modern times, is that typical or average brick masons do not know how to do historic restoration. In fact some of the worst damage and improper work is often done by professional masons. Just because someone is trained in laying brick though doesn’t mean that they understand how to restore historic masonry. The process of repointing or tuckpointing is entirely different than the process of simply laying new modern brick and mortar wall assemblies.
In understanding the differences between the brick masonry tradespeople used in the different types of historic construction, it helps understanding more about the four differences listed above. In the sections below we explain each of those four differences in more detail. Understanding these details sets a background from which it’s easier to understand the differences between the types of masonry skills and trades people.
Substrate material consistency
If you break apart old common bricks it looks like the people who we’re molding those bricks we’re literally shoving handfuls of mud into the brick forms. You will literally find pebbles and lots of different inconsistent materials inside of common bricks when you break them apart. Once in a while you can even find common bricks that show little traces of the face of a stone in the surface of the brick itself.
By comparison, pressed bricks were made with sifted clay. Essentially once the clay was extracted and dried, the clay was then sifted to remove or cull any materials that were larger than small granules. In historic times, without the use of hydraulic equipment, this was a very arduous process. Literally, tons of material had to be lifted up and sifted, just to make enough brick to build a portion of one wall. This higher level of consistency resulted in a much better brick. The brick was therefore not just more consistent in substrate materials but more importantly also dimensionally more consistent. When clay is fired in a kiln, the shape is distorted a little bit, but the level of distortion is much smaller if materials are more consistent. In order to build a pressed brick facade wall, this level of consistency is required for the thin mortar joints associated with pressed brick. The thin joint is referred to as a butter joint.
The picture below shows an example of a typical historic brick wall. By comparison to the pressed brick, the common brick construction assembly looks rough and rustic.
Firing temperature and duration
In addition to being more consistent because of the substrate material homogeneity, the press bricks were also fired at a much higher temperature and for a longer firing time. Often we will find areas of common brick walls with significant deterioration associated with low temperature firing. High temperature firing, by comparison, leads to a stronger brick. Bricks change form on a molecular level when fired. They become semi-vitreous. When fired at a higher temperature the amount of vitreousness of the brick is higher and therefore the brick is less permeable and stronger. By comparison, common bricks are weaker and have higher permeaability.
Ratio of lime to mortar
Even though much thinner, pressed brick joints are usually made with a much stronger and lower permeability mortar, there can be over twice as much lime in the pressed brick mortar joints than in the common brick mortar joints. Along with all of the other factors we talked about which make the pressed brick stronger, this is yet another factor which makes the walls built with press brick more durable, over time.
Finer tolerances in setting
We mentioned the noteworthy butter joint, a distinct type of historic brick mortar used in pressed brick. This mortar is applied in very thin joints, generally about 1/4 of an inch in overall thickness. In the bed joint that is a quarter inch in height and at the perpend joint that is a quarter inch in width. In the mortar itself, the materials are also sifted to omit or remove the coarse aggregate and chunks of slaked lime found in the common joints. There’s a bit of a general misnomer and general misunderstanding in the industry. Modern brick joints generally have a mortar joint thickness of approximately 1/2 to 5/8 of an inch; however, in historic common brick, the mortar joints could be very large, in some cases up to in 3/4 of an inch, in exposed walls. In concealed walls, such as demising walls intended to be covered in plaster, the mortar joints can be even as large as over 1″ in thickness. A one inch mortar joint is massive in comparison to the butter joints found in pressed brickwork.
Another picture of a similar wall follows below. This particular section of wall is where the adjacent building’s roof met below this particular building’s roof line. The area where the king hoist was set into the common brick at the demising wall is rough and the brick units are laid haphazardly.
Taking the material considerations into focus it’s easy to understand the differences between the trade work being done by the two different classes of workers. The general contractor, in contrast to how modern construction is generally conducted, built the three sides of the building where pressed brick was not used.
Front lumpers would come to the site for each of these buildings, just to build these front facades where press brick was installed. The difference in the tolerance between press brick and common brick is massive, a night and day difference.
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.
