The Infinity Design Solutions articles, on our website ids-dmv.com normally focus on the techniques and methodology related to historic preservation and restoration, particularly historic brick and mortar tuckpointing and repointing for preservation. Today, we’re taking a look at an interesting historic building with a completely modernized rebuilt structural interior. This particular building provides a very interesting perspective because the interior is completely unfinished, basically a blank or “white” space, so we have an unique opportunity here to see the bare bones of the hard structure of the masonry and concrete superstructure of the building.
With technology changing around us, seemingly faster than ever, it feels like construction and building techniques are one of the few things in our world that hasn’t changed drastically with modern technology. Workers still toil with the heavy burden of lifting much of the buildings mass into place, unit by unit. Tradesman are still need to have refined and hard-earned skills to perform their respective trade. When you look closely though, there are many changes in the technology related to materials and methods of installation that have changed and amount to somewhat drastic changes in the overall methods of building construction. (Still yet, a revolutionary seed change, when workers and journeyman skills are replaced by AI and robots still feels far off, for now.)
The outline of today’s discussion follows:
The principle elements of the superstructure and load path
The majority of historic brick row homes and masonry buildings in the oldest parts of Washington DC such as Capitol Hill are built with an exterior structural shell. That portion of the building supports all of the dead load of the floor systems and furniture and even the live load of people on the inside of the building, when people or furniture are standing on the middle of a floor in a room. For example, that floor system bears into pockets in the historic brick side walls of the building and those historic brick side walls of the building then transfer that weight from the floor system down to the footings, underground below the brick in the basement or crawl space of the building, generally buried relatively deep underground. By comparison, in modern construction footings are generally set at least a few feet underground, below the frost line but that’s not always the case with historic construction. Builders, over 120 years ago at the time of the start of the massive amount of construction that took place in historic districts of DC, such as Capitol hill, builders were aware of the impact and importance of burying footings below the frost line, but sometimes footings were put a little bit more shallow than they would be built today.
Transfer beams to open the floor space
This particular space though is different than the typical Capitol Hill row home or regular row building. There are several areas of buildings in Washington DC where commercial strips appear a little bit similar at the front facades of each respective building. They do appear historic, but there’s a big difference. Many commercial buildings are built extra wide to allow for the greater space needed in a commercial operation whereas a typical row home has regular floor plans with living rooms, bathrooms, bedrooms and hallways.
In in some cases, these commercial buildings have been joined together and even expanded, in some cases doubled or even tripled to make extra large gathering spaces or entertainment spaces for establishments such as restaurants. Often, in historic buildings, converted to restaurants, you may notice columns at the interior of the open space.
This building is built in a similar type of way, but the entirety of the interior of the building framing has been removed and replaced with modern construction, with the exception of the front facade. This gut and rebuild allows the interior to be built with entirely modern materials and methodology. Instead of using wood trusses for the girders and floor system, steel beams and concrete decks span the space horizontally.
The next picture below shows a transfer beam which supports a portion of the concrete deck. Concrete decks are generally built with internal deformed steel reinforcement bars. In some cases larger span openings will be built with a two-way or four-way post tension or pretension system where highly tensioned strong cables are used in compressive force in lateral direction with the slab to give the slab resistance from tensile deflection.
Here though, by comparison to larger commercial concrete buildings, this system is relatively simple and post tension or pretension cables are not used in the interior space of the slab. Deformed rebar is used, but not tensioned, just internal to the concrete deck to provide tensile resistance. Compressive strength is inherent in concrete, meaning that concrete can essentially resist being smushed between heavy forces, inherently or natively, as a elemental nature of the concrete itself. However, concrete and masonry for that matter as well do not have inherent significant tensile strength or force resistance. When positioned or used in a configuration which requires tensile resistance masonry and concrete generally require implementations or alternative methods of combination with other materials to provide additional tensile force resistance strength.
The steel beam in the photo below spans from a column to the top of a block wall. The block wall is vertically reinforced with concrete in every other cinder block vertical cell run. For this reason the block wall has relatively strong compressive strength and the spanning steel beam can support the column header although it doesn’t need much support, but it can also support a portion of the concrete deck above. In this case the space between the steel beam and the concrete deck has been filled with a non-shrink nonmetallic grout. In the picture below the grout looks very similar to regular high strength concrete but it is actually a different material without the typical variety of larger aggregate normally found in concrete. The non-shrink grout is applied after the beam is installed to fill the void between the concrete deck above and the steel beam. This grout then transfers the load of the deck to the steel beam.
A closer view of that non-shrink route atop the shop primed steel beam follows below.
Another similar transfer beam is installed between the block wall and the elevator shaft. At the edge of the cinder block shaft wall, you can see a remaining portion of plywood form board. Plywood form boards are used to create a temporary deck upon which the steel reinforcement and wet concrete are laid before they harden in the casting and curing process. Once the concrete is hard, essentially cured for a period of at least 7 days, varying and depending on the type of concrete specified and used, the plywood will be stripped and removed. In this particular case though the remaining board shows an example of what the entire deck would look like at the time of pouring the wet concrete. Those plywood form boards are generally supported by a large aluminum and wood beams set on structural scaffolding, used in the temporary forming and shoring assembly, those aluminum beams are most commonly, A21 beams. The “21” in the name denotes the 21 foot length.
Insidious damage from openings in the building shell
In this particular case, construction has stopped during the pandemic between phases of construction. The job site has been abandoned and the areas of the roof are unfinished and the stair and elevator shafts are wide open without a roof or membrane to protect the building from the exterior elements of weather and precipitation. Water has been seeping into the building for some time and has caused damage and deterioration, similar to the deterioration we find at historic brick masonry facades, but slightly different.
The block in this building is built with a type-S mortar. Historic brick masonry, for example, is generally originally built with a low compressive strength high permeability lime mortar. Although historic brick and associated mortar generally has lower compressive strength and higher permeability it can remain relatively undamaged from the majority of typical weather patterns if pointed or repointed or tuck pointed on a proactive schedule.
Similarities to historic masonry
Exposure to weather and precipitation will inevitably lead to the deterioration of historic brick mortar, if historic facades are not properly maintained or protected.
Mortar, especially historic brick mortar is porous, (by comparison, modern mortar such as high strength Portland motor has much lower permeability yet still is not completely impermeable or undamaged by the deleterious effects of exposure to precipitation) it can absorb water, and even wick water inwards through capillary action at open voids and even through microscopic voids and capillaries. When mortar is exposed to rain or high humidity levels, water can penetrate the surface and infiltrate the mortar joints. This can weaken the mortar and lead to its deterioration over time.
In climates like Washington DC, the presence of moisture in mortar can be particularly damaging. When water within the mortar freezes, it expands, causing internal pressure. This expansion can result in cracking, spalling (surface flaking and delamination), or disintegration of the exterior surface of the mortar. With repeated freeze-thaw cycles, the damage can worsen at a nonlinear, accelerating rate.
Efflorescence is a white crystalline deposit, similar to the salt we are most familiar with, which appears on the surface of mortar and masonry through successive cycles.of hydration and dehydration. The process occurs when salts present in the mortar dissolve and The next picture below shows a different motor joint with clear signs of Biocolonization or plants or moss growth on the surface of the block at the mortar joints.
Periodic repointing or tuckpointing involves removing damaged or deteriorated mortar and replacing it with fresh mortar, can help restore the integrity of the masonry structure. Care should be taken to use appropriate restoration methodologies and appropriate historically compatible materials that do not further harm the mortar and or lead to accelerated deterioration of the masonry construction or facade.
As always, it is important to note that when managing the preservation of historic structures, guidelines and principles should be followed to ensure the appropriate methods and materials are used for maintenance and repair. Consulting with historic preservation experts such as Infinity Design Solutions is recommended to ensure the proper care and preservation of historic mortar.
The picture below shows an area of the open floor of the building. Rainwater has entered the building, unmitigated for an extensive amount of time and cause damage, not just to the walls, but also to the concrete floor system. This damage can be repaired and halted in place. Once the building is dried and repaired, conditions can be ameliorated.
One of the several places where the roofing system is completely omitted is shown below at the future elevator shaft.
Working with concrete floor deck systems is significantly different than traditional historic wood framed systems that use a tight joist layout covered with a wood floor sheathing. In historic and contemporary wood frame systems, holes can be drilled or bored through floor systems to allow the passage of plumbing pipes, drains, and vents. Here though, for example in a concrete deck system the layout of plumbing piping must be measured and planned ahead of time so that blackouts or poor stops can be cast into the concrete to allow later passage of pipe runs. As an alternative to proper planning, core drilling of concrete is also an option, but generally significantly more costly than proper planning.
Opening spans and header requirements
Before the advent of mass production steel mills and ensuing relatively low cost steel and precasting cement plants (generally requiring the re-invention and use of Portland cement) availability for building construction, alternative historic methods of opening headers involved pure masonry and hybrid masonry-wood headers. Roman headers which are self supporting but require headspace are common in large floor to ceiling height buildings. Often though shorter segmented brick headers were used in Washington DC and Capitol Hill.
The picture below shows a closer view of a masonry lintel. The masonry lintel is cast and cured in an off-site factory. It’s not visible from the surface, but embedded in the masonry header, deformed steel reinforcement bars are inserted to provide tensile force resistance.
Historic masonry upkeep and preservation
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.
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, contact us or fill out the webform below and drop us a line. We will be in touch if we can help.
