Architectural and structural engineering drawings often show sections of building elements and details almost like a blow up plan of mechanical drawings. Actual seeing the inside of those conditions, gives you more inside into how these structural assemblies are actually built. They look a lot different from the outside, and the outside is generally the only part building users, pedestrians walking by and average people ever get to see. In the creation of this article we took a closer look at some open building assemblies to show the inside of those masonry walls, areas you don’t normally see.
In the picture below, you can see the ruins of a broken apart stone wall. This wall is over a 100 years old. At the left and right sides of the picture, you can see the edge of the exterior wall faces, also known as building facades. Between those 2 vertical masonry wall faces, you can see the interstitial interior materials that you normally don’t have the opportunity to see from the outside. Here you can see the small filler stones and pockets of mortar that were used to fill voids and build the wall up to accommodate spaces between the odd geometrical shapes of the stone and rock. This is a rubble wall. In this type of construction, mortar is used to fill those voids of varying shape and size.
By comparison an ashlar masonry wall has masonry units, whether of stone or brick, which are dressed to a rectilinear shape. In that type of scenario, motor joints generally have a very consistent bed joint and perpend joint mortar thickness. Ashlar masonry is not always built with units of of similar size from unit to unit, but ashlar masonry construction is generally rectilinear. The particular stone of this wall is a high strength stone, very similar to granite stone. The mortar, the cohesive binder is a historic lime mortar.
In the photo of a similar masonry wall ruin below, you can see the same sort of interior view of the wall as shown in the picture above. However, In this case though the wall is made with red clay bricks. These bricks are similar to historic bricks but they’re actually higher temperature fired bricks. Nonetheless, the wall was built in a similar way. This wall happen to be hit by a motorized vehicle and we took this picture before the wall was rebuilt. From an educational perspective, this gives us an opportunity to examine and understand how the wall was built many decades ago. Historic masonry walls generally have little to no steel reinforcement. However in this wall you can see a deformed rebar which remains sticking out of the broken ruins of the kneewall. That rebor provides horizontal lateral reinforcement.
In the adjacent architectural wall section detail below you can see a construction plan for building a masonry walled structure. This is a wall section of a historic masonry wall. This is a solid brick wall, the majority of the span of the wall is triple wythe masonry assembly, meaning that it is a three bricks thickness construction. That three brick thickness is typical of Capitol Hill construction for commercial and large buildings, at above grade walls of comparatively heavy construction. By comparison, smaller span and lighter load walls, such as historic residential row homes will often be double wythe wall construction.
There are a few different types of bricks used on the majority of historic buildings in Washington DC. The most common of all is called a “common” brick. Common bricks were low temperature fired masonry units. That means that they were fired in a large kiln with thousands of other bricks but at a comparatively low temperature, generally from a heat source using organic materials. By today’s standards, bricks are fired at a much higher temperature. The modern higher temperature kilns use combustion fuel such as propane, and the much higher temperature allows the brick to become near a vitreous. That higher temperature allows for a higher level of impermeability and a higher compressive strength. However higher temperature fire bricks also become increasingly brittle like glass, as is typical of near vitreous stone or earthen materials, such as historic clinkers.
The 2nd most common type of brick used in historic buildings is called a pressed brick. By comparison a pressed brick has a much higher amount of consistency, from brick to brick, in terms of dimensions and size. The press brick also is is more consistently rectilinear and truer to shape. Pressed brick substrate materials such as dried clays were filtered at a much finer sieve level then in the case of common bricks.
By comparison, the common bricks would often have stones or rocks and clumps of mud mixed into the brick itself. Those impurity impurities and inconsistent substrate batch materials would cause the bricks to slightly deform in the firing process, in a inconsistent way from one brick to the next. Fine mortar joints have always been considered a sign of superior workmanship. With the superior consistency of the pressed bricks, historic masons could achieve a consistent fine mortar joint. The thin water joint between press bricks is called a butter joint in Washington, DC historic masonry construction. By contrast though, the common bricks would require a larger mortar joint to accommodate and hide the inconsistencies in the shape and size of the bricks themselves. These differences become very obvious when tuckpointing exterior masonry facades.
In this article we talked about the following terminology and concepts related to historic masonry and historic brick restoration and tuckpointing., follow the links below for more related information from the IDS website:
- Construction drawings
- Construction Blow up plan
- Mechanical drawings.
- Building assemblies
- Building facade
- Rubble masonry
- Ashlar masonry
- Dressed masonry units
- Rectilinear shape.
- Bed joint
- Perpend joint
- Granite stone
- Lime mortar.
- Red clay bricks
- Higher temperature fired bricks.
- Steel reinforcement
- Deformed rebar
- Lateral reinforcement.
- Architectural wall section
- Brick wythe
- Common bricks
- Low temperature fired masonry
- Organic materials
- Vitreous materials
- Earthen masonry
- Clinker bricks
- Pressed brick
- Butter joint
These concepts are part of the fundamentals of stone and brick masonry, site hardscaping / hardscape, civil construction, historic masonry restoration, and building 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.