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Top 10+ Prevalent Threats to Masonry Structures

Here is crucial information on the top ten most common threats to masonry structures

Last week, we looked at 5 of the best ways to determine if brick mortar was historic or modern, at this link, and the week before, we looked at ways to discern whether a brick is historic or modern.  You can take a look back at that article at this link.  Today we look at another really interesting topic: The Top 10+ Prevalent Threats to Masonry Structures.  This topic will actually be broken down into two separate installments so we can give our readers the best experience with great details on the building science, technology, and history of these topic areas.

If you look at a masonry building, there’s no need to worry about it falling down or falling apart before you eyes.   Masonry is strong, durable, resistant to fire, resistant to most types of water.  Masonry is something you can depend on, they’re stable and solid, for the most part.  Masonry buildings take decades, even centuries to deteriorated to ruins.

Yet, masonry buildings, over long spans of time deteriorate significantly from external factors.  This happens slowly, but the cost and level of impact of this slow deterioration of masonry buildings is significant.  Today, in this article, we take a closer look at factors that cause deterioration to these old buildings.

The below image shows an example of a historic brick building where an adjacent demolished ruin was removed from where it was previously attached to the remaining building.

threats to masonry structures and demo side of brick building

There are many factors and forces that threaten the long term stability and typical life-cycle of a brick masonry building.  Those forces are even more extreme and amplified as they affect historic buildings, such as our beautiful historic brick buildings in Washington, DC.

Some of the top threats to historic brick follows below:

  1. Improper tuckpointing and scam pointing
  2. Free-thaw cycles
  3. Binder disintegration
  4. Differential settlement and lintel failure
  5. Lateral deflection
  6. Expanding embedded ferrous hardware and reinforcement
  7. Rising damp
  8. Bio-colonization
  9. Unmaintained paint
  10. Ferrous oxidation staining
  11. Leaking flashings and cavity vents

Improper tuckpointing and scam pointing

Improper tuckpointing and scam pointing are both so prolific and so damaging to a building that we consider them to be the number one biggest threat to masonry buildings. Every brick or masonry building needs to be tuck pointed at some point in its lifespan.  When a building is built right, it can potentially last for hundreds of years.  Masonry units, the brick itself, for example can be very strong but the mortar should be intentionally considered a sacrificial weak link.  This is deliberate, intentional, and it benefits the walls of a building overall to have the bricks be stronger than the mortar.  There are many potential and significant mistakes made by nonprofessionals when carrying out pointing work.  The consequences of improper pointing work are staggering.  Brick pointing is the act of removing mortar where deteriorated at the outer face of the wall to a depth of about no more than 1.25 inches from the face of the wall inwards, and then carefully applying new proper mortar to that void.

The picture below shows an example of where pointing was needed for years at a brick masonry window header. Instead of pointing properly, the building owners hired someone or improperly did the work themselves to install calling at deteriorated mortar joints which resulted in greater damage.  Doing something like this is as bad as building vandalism. It causes the already deteriorate and mortar joints to continue deteriorating but now at an accelerated pace making the damage worse and occur even faster.

window-header-tuckpointing-needed

When pointing is done correctly, once the mortar is removed, it is then the wall is then wetted and to prevent excessive wicking of the new mortar, and then new mortar is installed in lifts, by hand. It’s a very tedious process and it has to be done by trained professionals. Otherwise, without trained tradesmen, untrained laborers install incorrect mortar types which are too hard for the wall.   They could also install the new mortar at improper depths.  Scam pointing, for example is the application of a thin layer of mortar on top of a deteriorated joint without raking the joint properly prior to installation of mortar. It sounds benign, but this type of scam work is extremely destructive. It can lead to failure of the brick masonry wall and destruction of the individual comparatively delicate bricks.

spalling-of-brickThe adjacent image shows an example of a brick wall where brick faces have significantly spalled as a result or improper pointing.

We recently had the good fortune to talk to John Speweik, a renowned expert, writer, and educator in the areas of historic masonry restoration.  We talked extensively about the damage caused to historic brick masonry by improper pointing and you can read more about this topic at the following link: Types of Damage Caused by Incorrect mortar in Brick Pointing

Some of the many reasons that this type of damage isso devastating is that it’s generally done in a wholesale type approach, to an entirety of the building facade which means that unlike other types of damage which occur at a particular spots, this can affect the entirety of a building exterior.  Also, where other types of damage can be treated and repaired, this type of damage is extremely expensive to repair. This is one of the many reasons why it’s important to hire a trained serious professional like Infinity Design Solutions.  Establish a rapport with a contractor you trust and who is trained and knowledgeable about masonry restoration because hiring someone else for a type of job like this where trust and responsibility is required can be devastating.

Free-thaw cycles

Significant damage can be caused from expanding water at freezing temperatures, and the cyclical nature of freeze-thaw cycles.  However, to understand this topic, it’s important to understand that freeze-thaw cycles generally cannot cause that much damage without other problems happening concurrently. Once a mortar binder is disintegrated to the point that water can enter the mortar joint with ease, then build-up occurs much more prolifically.

In cycles of precipitation, as deteriorated mortar joints are hydrated, as those cycles of precipitation happen with intermittent freeze-thaw cycles, the wet or saturated mortar joints become filled with ice.  As water freezes, it expands, with significant pressure.  The mechanics at play in circumstances of freezing pipes, cause pipes to burst, for example.

The same forces cause masonry to chip and break and spall at the surface, as the freezing water expands with pressure greater than the tensile resistance of the brick masonry.  Free-thaw cycles can also cause water to work upwards or against the natural flow of water through a phenomenon called ice damming.

All of these conditions are compounding negative factors that allow precipitation and / or hydration to under brick mortar joints and then cause damage through expansion.  Engineering formulas can derive the potential volumetric expansive force of freezing water, as it affects masonry joints, cracks, and crevices, factoring for elastic properties of masonry assemblies.  Certain conditions can experience volumetric expansion over 9%, so the possibility of damage is significant.

This topic, again, highlights the benefit and importance of proper pointing on a proactive timetable to prevent points of potential damage in masonry assemblies, such as the historic brick walls of our buildings in Capitol Hill, Dupont Circle and Georgetown, in Washington, DC.

The below image shows an example of a brick wall, at a stage of significant deterioration.   This picture is current and recent, taken at the time of writing the article in August 2022.  It’s only a matter of short time before the building is either restored or this wall will end up collapsing under its own weight and the natural building movements associated with the inherent movement of subsoils, wind and weather.

brick-binder-disintegration

Binder disintegration

Mortar is generally made from two main components,an aggregate and a binder.  In historic brick mortars, There is generally only small variation from one construction to the next, but in a common brick assembly,the mortar is mostly aggregate in the form of sand.  Lime, works as a binder, similar to modern Portland cement in modern construction. But in historic mortar, the lime alone was the binder which held the aggregate together and gave the mortar joint its compressive strength.  Neither Portland nor lime mortar are perfectly impermeable to water, but lime mortars are comparatively highly susceptible.

Binder distribution is slowly happening throughout all of the historic masonry buildings.   Areas with more exposure to elements, water, and wind will deteriorate at a faster rate, but by and large the only real method for upkeep, maintenance, and prevention of extensive deterioration or resulting damage is the ultimate damage is improper tuckpointing.   Our company is dedicated to proper tuck pointing and we talk about the methodologies and principles of proper historic masonry restoration throughout our website and blog.

Differential-settlement-brick

Differential settlement and lintel failure

Differential settlement and lintel failure are two separate and different items, but they’re closely related.

Differential settlement is related to subsoils moving or shifting below the weight of building footings at differential rates. In other words, if a subsoil below a footing moves lower or succumbs to the superimposed building weight above at a rate faster or greater to other parts of the same building, that is differential settlement.  Footing subsidence is problematic, in general, but in many cases even settlement is much less problematic.  On the other hand, differential settlement can be extreme enough to cause problems such as propagation cracking, unlevel building floors, and even go far enough to tear a building apart.

Lintel failure is very similar. One of the biggest differences is that lintel failure can happen as a result of or even independent of differential settlement.  In Washington DC, with segmental brick arches, one of the most common reasons for lintel failure can simply be deterioration of the mortar joints. After mortar joints deteriorate, water can enter the masonry partition through those open joints, with voids and deterioration of the mortar and then cause rot or damage to the internal structure of thearchway. Unlike Roman arches, segmented arches are not fully, truly self supporting.

As well, segmented arches similar to all types of opening arches are significantly affected by differential settlement and can fail as a result of differential settlement even independent of mortar deterioration. In most cases though, mortar deterioration will be a compounding factor even when the primary cause of lintel failure is differential settlement. This is largely the case because of the age of historic brick buildings. In Washington DC, to some degree there is generally some amount of mortar deterioration present and coincident with lintel failure.

One are the first signs of differential settlement or lintel failure in brick buildings is stair-step cracking and can next lead to lateral deflection.

lateral-deflection-bowing

Lateral deflection

Lateral deflection is the bowing of masonry walls.  This sort of disintegration happens over time as mortar loses its cohesive strength, the wall, under its own massive weight of its own brick masonry, loses strength and starts to bow and curve.  Often issues of lateral deflection are coincident with areas of stair step cracking caused by failure header or differential settlement. These things often happen in combination or as a precursor to lateral deflection.

Iron or steel implements are often added at the sides of masonry walls to prevent or resist the forces of lateral deflection.  In the photo below you can see an example of a barnstar installed at the sides of a building in Washington, DC.

This type of issue happens as a result of compounding forces of deterioration, a combination of problems in the middle of the deterioration curve.  At a point when lateral deflection begins, deterioration continues but increases exponentially because the lateral deflection itself causes the separation and enlarging of mortar joints, essentially splitting them apart at particular areas of the wall and crushing them in compression at other areas as the wall bows out of the original planar form.  As the geometry and shape of the mortar joints change drastically, in this process, the joints in the area of lateral deflection open and enlarge which allows weather to enter more easily.  In the process, additional deterioration results through the joints being opened and now more susceptible to exterior elements.

iron-steel-implements

Next week we will continue discussions on this topic, we will cover more topics related to sources of masonry deterioration such as: Expanding embedded ferrous hardware and reinforcement, Rising damp, Bio-colonization, Unmaintained paint, Ferrous oxidation staining, Leaking flashings and cavity vents.

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.