Following is a discussion of the top ten prevalent threats to masonry structures
Last week, we looked at 5 of the top !0+ biggest and most prevalent threats to masonry structures. You can see that article at this link, in case you missed it! This week we are looking at 5 more of the biggest threats to the long term stability of both modern and historic masonry structures in today’s article: “The Top 10+ Prevalent Threats to Masonry Structures, PART II“. We broke this topic down into two separate installments so we can give our readers the best details on the building science, technology, and history at the heart of these topic areas.
Last week we delved into the following 5 topics:
- Improper tuckpointing and scam pointing
- Free-thaw cycles
- Binder disintegration
- Differential settlement and lintel failure
- Lateral deflection
This week we continue on a journey of the scientific understanding of brick and masonry building construction and preservation by looking closely at the following 6 topics:
- Expanding embedded ferrous hardware and reinforcement
- Unmaintained paint
- Ferrous oxidation staining
- Leaking flashings and cavity vents
Expanding Embedded Ferrous Metals
Ferrous metals are any and all metals that contain some iron. Most metals we see and touch on a regular basis are alloys: mixtures and combinations or multiple types of metals. Iron, in its raw natural form, is almost never seen as just pure iron. More often, it is found, in earth, as iron oxide, a form of rust.
Metals are embedded and installed into masonry and concrete, and brick mortar joints for a variety of reasons. In some cases, reinforcement bars used in concrete, embedded directly into the middle of the concrete To resist deflection and provide tensile strength. Concrete and masonry has significant compressive strength, but generally lacks tensile strength. Steel reinforcement provides significant tensile strength when used in combination with brick masonry or concrete building assemblies.
Steel embedments, also known as embeds, are also often used to attach additional or accessory elements to buildings and in some cases fasteners are used to mount other structural or non-structural elements directly to masonry or concrete.
The picture below shows an example of a concrete front porch in northeast Washington DC. The concrete slab edge is spalled and significantly deteriorated. The ferrous reinforcement bar, also known as rebar, has rusted and deteriorated. Signs indicate that the front porch gutter was leaking right onto this location for an extended period of time. With the concentrated exposure, overtime, the significant hydration caused the rebor to rust to the point that it expanded causing the concrete to spall and fracture.
Similar to the issue described above, the picture below shows a modern brick construction with a steel angle iron lintle. This lintle was never properly coated to rest oxidation and as a result has also rusted. This particular little hasn’t yet oxidized to the point that it has expanded significantly. Without proper coating and application of a gun-grade elastomeric sealant, it will oxidize and lose structural capacity and expand to the point that it will crush the adjacent superimposed brick. Over time the condition will continue to the point that the brick is significantly damaged beyond repair or destroyed.
An additional picture follows below. This picture shows a similar window opening, but in this case, the lintel has been coated with an exterior grade paint. That paint helps preserve the steel; however a sealant between the lintel and the underside of the brick above is missing. That sealant is important because wind driven rain, water running down the face of the brick, or ice melt will enter into the cavity. Once water enters into that cavity, it will dry very slowly and cause deterioration in the meantime.
Bio-conization is the growth of plants or other biological sporal materials in or on masonry surfaces or brick mortar joints.
Both lime mortar joins and modern portland mortar are affected or susceptible to bio-colonization, in states of deterioration. However, historic lime mortar joints are significantly more susceptible and risk damage from bio-colonization. Once deterioration begins to occur deterioration continues at an increasing rate.
We have examined some of the fascinating details related to biocolonization in masonry facades in some of our past articles. Click the links below to learn a lot more:
How To Keep Plants Out Of Your Mortar Joints
Ivy Growing on Masonry Building Facades
The examples of bio-colonization described in the articles above, highlight some of the extreme cases where ivy and fern Are growing with root systems deeply embedded into the brick mortar joints.
Other cases, however, exist where even moss, a nonvascular flowerless plant, and other small plant growth can propagate on the surface of and into the deteriorated mortar joints. This level of smaller plant also poses a threat to masonry construction assemblies. Over time, the brick mortar joints become increasingly deteriorated as plant roots grow deeper into the joints. As well, like any type of ecosystem with plant growth, over time as mortar joints continue to deteriorate larger plants will take root and cause increasing damage.
The image below shows a similar example of small plant growth on a brick masonry wall, but in the case of the photo below, this example shows plant growth, not just in the mortar joints, but also on the face of the clay brick. Brick units are generally less permeable than deteriorated mortar joints. However, in many cases historic common brick will have cracks at the outer face of the brick. Those cracks can provide a perfect breeding ground for plant growth. Since historic common bricks are considered to be low temperature fired bricks and therein lower compressive strength, the inner part of the brick is comparatively weak and susceptible to deterioration from both moisture and plant growth.
- The painted brick homes of Washington DC are beautiful, but before you paint a brick surface, if it has never been painted before, you should really consider alternatives. Painting itself isn’t terrible for the brick, but it can lead to accelerated deterioration of brickwork for a few reasons. The largest of these reasons is that when paint begins to deteriorate and delaminate, It can trap water behind the delaminated surface of the paint. The void or loose partially delaminated paint covering will trap and hold water, and therefore the amount of time that the brick is exposed to precipitation leads to higher incidents of hydration. (You can read more about the nonlinear nature of the typical deterioration curve and the natural tendency for deterioration to accelerate over time at the following link: accelerated deterioration
Ferrous Oxidation staining
- Ferrous oxidation staining is simply rust stains on the exposed surfaces of brick masonry and concrete. Stains of this type destroy the aesthetic quality of a building facade. These stains can be removed with chemicals and / or abrasion, but harsh chemicals and / or overly aggressive mechanical cleaning can damage the exterior surface of brick masonry. Once the surface is damaged, the subsurface of the brick becomes exposed and then allows future ingress of moisture which accelerates deterioration of the masonry facade.
Leaking Flashings and Cavity Vents
- Really, this item is two items in one. Flashing is technically different than cavity vents, but flashings generally span between or through material types. In the case of a cavity vent, an opening that runs from the outside of the building through to the inside of the building is similar in the way that a cavity event works like a flashing and goes through or spans above or in the middle of the dissimilar materials.
- Flashings, such as rooftop parapet copings, at the top of masonry walls, are essential to keep masonry dry at the internal filled space between brick wythes.
- In the adjacent image, you can see an example of a deteriorated roof system, the coping that was once installed on the top of the brick wall parapet has blown away in the wind and was never properly replaced even after significant time has passed. In this particular example, at this building, water has slowly seeped in from the top of the wall
As a result, advanced or accelerated deterioration of the brick has occurred in the double wythe brick wall assembly. As you can see today, in the photo below, there is significant bricks spalling and deterioration of the brick assembly. Essentially, once a brick wall is allowed to begin to deteriorate, deterioration continues at an increasing or accelerating rate.
Cavity events, usually made from cast iron and seldom lyrics from kiln fired terracotta or or kiln fired red clay brick, are found at the attic and crawl spaces of capital hill homes. These vents are built directly into brick wall assemblies allowing cross ventilation through crawl spaces and attic cavities. In historic buildings, at the time when they were built, over a 100 years ago, alternative methods such as light gauge coil stock flashings were not commonly available. From time to time wind driven rains will allow some degree of water entry and deterioration at these locations is common. This also, in some into the category of deterioration or damage caused by ferrous metal expansion.
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 following terminology and concepts, follow the links below for more related information from the IDS website:
- Portland Cement
- Lime mortar
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.