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Spalling And Exploding Bricks – Part I

What is Spalling (Exploding Bricks)?

Last week we discussed topics around facade leakage and types of resultant or causal deterioration.  This week we’re looking more in depth about spalling and a term known in the industry as “exploding bricks”. The bricks don’t really explode, so it’s completely a misnomer but it’s common to refer to the damage of this type “exploding”. This terminology happens to be used because the faces of many if the individual bricks will literally pop off of the brick itself. It looks like each failed individual brick has exploded but there’s no actual explosion happening in the process of deterioration.

More information on the phenomenon of brick spalling.

Today we looked at a rear rowhome extension. The building is a historic rohom come a built about 110 years ago, but in this particular case there is a rear addition that extends approximately 10′ farther back into the backyard of the property. On the neighbor’s side of the rear addition you can see that there is extreme deterioration at the historic brick. Even though the addition is newer than the original construction, the addition brick is still historic because the addition appears to be built around 70 to 85 years ago. That is newer than the original construction but it is nonetheless considered historic because the technology at the time of construction predates the use of automated or heavy hydraulic driven machinery and high temperature combustion fuels used in the brick firing process. We can tell that this is historic for a few reasons.

The picture below shows the extension or addition of a rowhome, originally built around the early 1900s. The picture is looking at the brick construction of the addition from the neighboring side of the lot line or property line.

addition of a rowhome

We will look closer at the following topics:

  1. How you can tell the age of a building addition
  2. Stucco application
    • Explanation of conditions 
    • Purpose of the stucco
  3. Explanation of spalling 
  4. Causes of Spalling
  5. Biocolonization 
  6. Options for repair
    • Sounding
    • Brick removal
    • Brick replacement 
  7. Proper brick pointing 

How you can tell the age of a building addition

Our website is filled with information on the history of brick construction in Washington DC. The majority of these buildings were built around the turn of the last century, between the late 1800s and the early twentieth century.

For reference,  take a look at other articles and entries in our encyclopedia of historic masonry restoration.  In addition to information related to best practices for repointing and tuckpointing of historic brick information, we have included a variety of information around brick building practices and methods and materials.

The following links include more detail on specifics. 

One ofthe fastest and easiest ways to tell if a brick is modern or historic is to measure the width of the brick. Generally, the most common building bricks are approximately 2.25″ tall, when laid in the most prolific disease position, the stretcher position.   This dimension applies near universally to both historic and contemporary bricks.  Bricks in a running bond, for example are all laid in the stretcher position.  There’s no variation or differences in pattern and configuration in the running bond.  (For this reason, the running bond is one of the fastest and cheapest of all bonds, but it’s unfortunately also one of the weakest and least stable of all common brick bonds.)  The wall below is built in a stronger but very similar bond called a common bond.  In every sixth course of the horizontal brickwork, the bricks are switched to a rowlock position.   The wall is built with a double wythe assembly.  The ‘whythe’ is the quantity of vertical layers of brick.   In this case, the wall is built 8″ thick, so it is made with two brick whythes.   Since the bricks change position at every sixth course, that alternating sixth course holds the two wythes together because the brick in each sixt course of brick is turned spanning between the 2 wythes.

The picture below shows a closer view of the stucco application which covers the majority of the exposed exterior portions of the wall. In the center of that picture you can see an area where one brick has spalled.   Spalling is a type of brick masonry or cement deterioration, where the face of the masonry or cement delaminates and separates from the original, greater remaining building assembly.

stucco application

The vast majority of building failures related to spaliing are caused by using improper mortar in the repointing or tuckpointing process. Repointing or tuckpointing processes are necessary at the exterior of the vast majority of masonry buildings built over 50 to 80 years ago. Around half of the historic buildings in Washington DC have already been pointed but many of them have been repointed improperly, with incorrect brick mortar.  Poverty was rampant in Washington DC, and during and in the decades following, through to today, the effects are long-lasting with building upkeep decisions, driven by a caveat emptor based real estate market priortizing short term repairs.  

Stucco application

Stucco applications are somewhat common at rear additions and parts of historic buildings in Washington, DC.  Stucco is used more prolifically and more commonly in other parts of the world, however, by comparison.  The differences between the types of materials used for masonry and/or stucco applications vary by region depending on factors such as the technology most prolific at the time of development or construction of the majority of the buildings in each geographic location.

improper mortar

Explanation of conditions

In this particular case, a two-part stucco application has been applied on top of the existing original brickwork. This particular brick work is not original to the first construction of the building. We believe that this brick was installed as part of the building addition approximately 20 to 40 years after the original construction.   Stucco is a type of cement rendering, similar to parging, mixed and applied by trowel onto the surface of the brick.

Purpose of the stucco

In many cases, stucco or cement renderings or parging coats of cement can be used to preserve or protect the substrate surfaces of brick masonry; however, by comparison, historic brick buildings do not need a stucco application. The brick itself, if maintained and preserved by repointing and careful maintenance, can last indefinitely as a semi-impermeable surface, appropriate for building construction without an additional application of stucco.

application of stucco

Explanation of spalling

Brick spalling can happen for a variety of reasons, but the phenomenon of spalling occurs when the integrity of the brick or brickworks in a building assembly become deteriorated and the internal elements separate from one another through deterioration or lack of functional binder.

 A picture below shows a close up view of the base of the wall, above the wooden rear deck at the neighboring property.   If you look closely at the picture, you can see that the internal elements of each of the remaining bricks look like a loose mixed mash-up of clay chunks and particles.   Although these bricks may have originally looked like solid rectilinear units, the internal elements of each of the brick units likely never reached full compressive strength and / or achieved a vitreous nature from fusion of the small internal particles, as is achieved through the high temperature brick kiln firing process.

spalling exploding bricks

Causes of Spalling

As discussed above, spalling can happen for a variety of reasons, some of the main reasons are deterioration of the brick are improper  pointing or use of a modern mortar ratio for repointing historic brick and / or use of a brick that is defective or fired at a temperature too low to reach an appropriate level of compressive strength and vitreous nature.

brick deterioration

In the coming week we will continue with part two of this two-part series on brick spalling and exploding bricks. We’ll pick up with the topic of bioconization, a different but related form of deterioration. Bioconization is a symptom or sign, and also a factor of ongoing and increasing or accelerating deterioration.

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.

In this article we talked about the terminology and  concepts of historic masonry restoration, follow the links below for more related information from the IDS website:

  • Binders in mortars and concrete
  • Brick burns 
  • Butter joint
  • Capillary action
  • Cantilever
  • Cementitious siding
  • Cheek wall, masonry — Draft
  • Chemical testing
  • Code, building — Draft
  • Cold joint
  • Cold weather masonry work — Draft
  • Damp proof course
  • Downspout
  • Electrical distribution panel — Draft
  • Fenestration
  • Ferrous metals
  • Great Chicago Fire
  • Green bricks 
  • Gutter, roof
  • Lime mortar
  • Lintel
  • Load path
  • Oriel window
  • Oxidation
  • Parapet coping
  • Plug, clay
  • Pressed bricks
  • Raking, of mortar joints
  • Raggle, aka reglet
  • Rectilinear
  • Roman bricks
  • Roman arches
  • Roof eave
  • Roof termination 
  • Row buildings and row homes
  • Sedimentary rock
  • Scratch coat
  • Sprung arch
    • Squint bricks, 
  • Strike, or striking of mortar
  • Tapestry bricks
  • Tooth-in, interlocking masonry connections
  • Vitreous
  • Water diversion systems
  • Zipper-joint

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, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.