This week we looked at five of the most common frequently asked questions (FAQâs) related to historic brick masonry restoration in Washington DC. Those questions and subsequent answers got into discussions on restoration and preservation, repointing and tuckpointing, and the technical areas of best practices of care for historic masonry structures and facades. A link to last weekâs article can be found here. Today we continue that discussion by looking at a new set of 5 of the most common frequently asked questions. Today we will talk about: We start todayâs discussion with FAQ #6 below, where we left off last week:
In the long-term, unmitigated or untreated mortar deterioration will lead to catastrophic failure of a building, eg. collapse. The brick walls of historic row homes in The historic neighborhoods of Washington DC such as Capitol Hill, Georgetown, and Dupont Circle, are structural walls. Unlike interior non-bearing partitions, structural walls support the dead loads and live loads of a building. The dead load of a building is the mass and weight of the building itself, whereas the live load of a building is the weight of furniture, furnishings and the inhabitants or users of a building. While we use the word catastrophic, and this kind of major failure is in fact catastrophic, you can often see obvious signs of failure slowly happening to a building long before a building starts to collapse. In a past article, at the following link,we looked at a collapsed rowhome rear facade: Learning Masonry Structure Anatomy From Old Ruins â Part IIn this fascinating case study, you learn about the foundation and load path of a typical historic brick rowhome and how the economic blight in Americaâs urban centers affected the choices related to mid-century restoration of defunct systems, often rendering fireplaces abandoned and unrepaired, especially after more modern and contemporary HVAC systems became available. The building in the case study was vacant and unprotected for years. Over time the brick mortar joints became neglected and deteriorated to the extent that the walls first experienced lateral deflection. Repointing or tuckpointing and restoration of the historic brick mortar could have reversed the natural effects of aging. Overtime, slowly the damage became worse and worse. Itâs true that masonry deterioration generally happens very slowly, yet the process of deterioration happens at an increasing rate. Deterioration is nonlinear. In other words, while historic brick deteriorates slowly, it happens faster and faster. Erosion begets yet more erosion, for example. Disintegrating mortar leads to yet more disintegration of mortar deeper within a brick wall assembly. The driving force of disintegration, erosion, and deterioration of mortar are the elements of nature and mainly exposure to water and hydration. This damage happens, invariably at mortar joints. Repointing or tuckpointing are the only way to preserve and stop the process of deterioration, but as the damage becomes extensive, it can lead to worse problems. The picture below shows the exterior episode of a structural brick wall in a historic building. The wall went without proper repointing for decades. As water entered and sat within the mortar joints, through the pressures of freeze-thaw cycles, the bricks cracked and spalled. The damage to this particular wall is so extensive that even from a distance, the deterioration is noticeably visible. Brick spalling refers to the gradual deterioration or flaking of the surface layers of brick masonry structures. This phenomenon primarily occurs due to the infiltration of water into the brickâs pores, especiallyin historic brick masonry like that which was commonly used over 100 years ago in Washington DC, followed by cycles of freezing and thawing. When water enters the brick, it expands as it freezes, exerting pressure on the brickâs internal structure. This repeated expansion and contraction stress lead to the disintegration of the brickâs surface layers, resulting in spalling. Additionally, chemical reactions, often the effects of which can be seen in efflorescence, between water and the minerals within the brick can indicate signs of deterioration leading to spalling. Over time, if not addressed, brick spalling can compromise the structural integrity of the masonry and cause significant degradation, making it a concern in the areas of structural failure as a result of a lack building maintenance over a long period of time.
This particular question is complex, but the bottom line is that issues with deterioration at mortar joints over extended periods of time, has explained in the FAQ above, lead to significant damage and even eventual catastrophic failure. Differentiating between a superficial cosmetic issue and a structural problem requiring repointing in historic brick masonry involves a careful assessment of several factors. First, the depth of mortar deterioration must be examined. It helps to engage a professional like Infinity Design Solutions. Superficial cosmetic issues typically manifest as minor mortar wear on the surface, often due to weathering and exposure to the elements. These cosmetic concerns may not affect the structural stability of the masonry, at first. In contrast, structural problems are characterized by deeper mortar deterioration, potentially extending into the the area beyond the surface of the mortar joint. Another aspect to consider is the presence of gaps or voids between bricks. Superficial issues might involve minor gaps or cracks, primarily affecting the mortar jointsâ outer layers. However, structural problems often result in more extensive gaps, voids, or even complete separation between bricks. These gaps can compromise the load-bearing capacity of the wall, making repointing necessary for restoring structural integrity. When the mortarâs integrity is compromised at this level, it can jeopardize the stability of the entire wall. After the mortar joints become destabilized, secondary problems often result in lateral deflection which leads to wall collapse or stair-step cracking which leads to header failure and collapse. In the realm of structural concerns, itâs important to understand that the mortar in historic brick masonry contributes significantly to the wallâs integral strength. Mortar joints distribute loads and provide cohesion between bricks. As erosion or deterioration progresses into the core of these joints, it weakens the overall structure. A skilled assessment, including probing the mortar joints and assessing the extent of wear, can help identify whether the issue is superficial or requires repointing for structural reinforcement. Proper evaluation and timely intervention are essential to maintain the stability of historic brick masonry structures. The picture below shows the front facade of a historic brick building, built over 100 years ago.
The choice of mortar used in repointing is critical in its effect on the longevity of a restored facade, and it involves a somewhat complex interplay of factors. Traditional historic brick mortars, often dating back a century or more, exhibited significant variation in both the types of aggregates and binders used. These historic mortars tend to be softer and more permeable compared to their modern counterparts. The key distinction is in the binder composition of these mortars. Traditional historic mortars often used slaked lime as a primary binder, with aggregate materials like sand and sometimes even crushed shells, foubd in some coastal areas (like the Carolinas with tabby Ruins along the seaside). These ingredients created a mortar that was relatively soft (on a structural engineering scale) and porous, allowing for flexibility and breathability. This was particularly well-suited to the older bricks and masonry materials used in historic buildings. Over time, this type of mortar could accommodate the natural expansion and contraction of bricks, with changes in weather and temperature, preventing damage due to typical shifts. In contrast, modern mortars commonly use Portland cement as the primary binder, resulting in a mortar mix with higher compressive strength and lower permeability. While this might appear to be an improvement in terms of structural resistance, it will invariably cause potentially devastating problems when used on historic brick masonry, in the repointing or tuckpointing process, for example. The rigidity of modern mortars can be mismatched with the relatively softer and more porous historic bricks, leading to unintended consequences. When subjected to structural stresses or environmental changes, these differences in material properties can cause stress points and even damage to the historic masonry. Moreover, modern mortarsâ lower permeability, when used in repointing or tuckpointing, can disrupt the natural breathability of historic walls. Moisture that would have been absorbed and released through the softer, more porous historic mortar can become trapped within the masonry. This can lead to increased risk of freeze-thaw damage, efflorescence, and spalling, all of which can deteriorate the bricksâ appearance and structural integrity. In essence, while modern mortars may offer advantages in terms of strength and longevity, they must be used judiciously in the context of historic brick facades. The choice of mortar type should prioritize compatibility with the existing masonry materials and take into account the buildingâs specific needs. This often involves replicating the historic mortarâs composition and properties, as closely as possible, to ensure the long-term preservation of the facade. In cases where modern mortars are used, careful consideration, and possibly consultation with professionals such as Infinity Design Solutions, is helpful to mitigate potential adverse effects on historic structures. The picture below shows a facade area where a leaking scupper head caused damage to the brick wall for years while the scupper went unrepaired. Later, when repairs were finally made to the brick, to the right side of the scupper in the photo below, the brick was reset in place by an untrained and unskilled worker and a modern mortar was used. Untrained or unskilled workers will often use incompatible mortars because modern mortars are available at local big box stores and compatible historic mortar is not available off the shelf at big box stores.
No, repointing or tuckpointing alone cannot fix problems of brick damage and deterioration such as cracking and spalling. Repointing proactively on a timely schedule can largely prevent this type of damage from occurring, but even after damage within individual brick units happens, even where it cannot yet be seen, it cannot be fixed by simply repointing. The only way to fix that type of damage is to replace the damaged units. As a side note, as we touch one here, damage can happen within the internal parts of individual brick units for a significant amount of time before those brick units even crack and/or spall or fall apart. The internal parts of a brick, once damaged from unmitigated exposure, are damaged permanently, and meanwhile the outer parts of the brick might not show that damage for years or even decades. Pointing and/or repointing or tuckpointing will not fix that damage that has already happened and even after repointing, if repointing is not done on a timely schedule, the damage thatâs already happened In the past can become visually apparent after pointing happens if that repointing doesnât happen proactively and preemptively. The picture below shows a closer view of a different brick wall where pointing has not been managed properly. This wall should have been repointed years prior to now and in the picture below you can see the condition of those open mortar joints where the mortar has deteriorated significantly now today. In the middle of the picture there is a brick that has cracked and spalled.
There are several types of upkeep and maintenance practices that should be followed by homeowners to protect the facade of a building from damage and deterioration. The pictures below show the work of an overzealous house flipper who added three large dormers to an attic space in a conversion to add interior square footage. The dormers did not initially account for an uninterrupted span of a gutter at the gable roof eave. Now the only practical solution is to have four independent gutter and downspout systems. It looks ridiculous, but itâs much better to collect and channel rainwater away from the facade. It was a big oversight, but at least the facade is being protected. The next picture shows the same facade from a different angle and you can see that the original line of roof eave has been interrupted by the new dormers. The following tips can help maintain a building for increased longevity:
The pictures below show an area at a window header, where a gap developed between the brick and the steel lintel after the lintel had oxidized and became dilapidated. This particular still lintel is the structural reinforcement which supports the flat header. This is an example of a very expensive repair that could have simply been avoided by routine maintenance of upkeep.
By following these maintenance practices and staying vigilant, homeowners can extend the life of a professional repointing job, ensuring the continued preservation of their historic brick facade. Regular care helps protect the buildingâs structural integrity and retains its historical character. <p>The post Top Historic Masonry Repointing FAQs â Part II first appeared on Infinity Design Solutions.</p> Via https://www.ids-dmv.com/masonry/top-historic-masonry-repointing-faqs-part-ii/
0 Comments
Leave a Reply. |
About UsInfinity Design Solutions LLC (IDS) is a full service general contracting company in the heart of the Dupont Circle neighborhood of Washington, DC. We focus on repair and renovation of buildings and facilities in both historic designated neighborhoods and the commercial-zoned central business district of the city. Follow Us
|