Learn more about spalling and exploding bricks
Last week we presented part one of this two-part series focusing on spallling and exploding bricks, a form of deterioration of brickwork, masonry and concrete that is common in buildings in Washington DC, particularly historic brick buildings built at the turn of the last century.
The outline of topics follows, and rotation we continue at the topics Biocolonization.
- How you can tell the age of a building addition
- Stucco application
- Explanation of conditions
- Purpose of the stucco
- Explanation of spalling
- Causes of Spalling
- Biocolonization
- Options for repair
- Sounding
- Brick removal
- Brick replacement
- Proper brick pointing
Biocolonization
Biocolonization is a symptom or sign, and also a factor of ongoing and increasing or accelerating deterioration in historic brick and other types of cement and masonry. Biocolonization is a big word, but the concept is actually relatively simple. When you see it for the first time it looks a little bit surprising and you might not even understand what you’re looking at, but what’s happening is relatively natural and understandable.
Essentially, as mortar deteriorates it becomes a material surface more similar to soil or sand and even similar to earth and dirt. You can understand this better by looking more closely at what brick mortar is actually composed of and how it’s made. Brick mortar is essentially not much more than small stone dust and particles and sand as an aggregate and lime as a binder.
The picture below shows an example of a historic brick facade where the mortar joints have deteriorated to the point of near complete failure. The remaining substrate materials at the location of the former mortar joints are now covered with an example of plant growth referred to as biocolonization.
The next picture below shows another photograph of the same area of the historic brick masonry facade but at a closer viewpoint or angle. You can see that the small plant-like life has taken root in the remnants of the mortar joints.
Options for repair
Generally, with masonry restoration there is a variety of types of repairs that may work for the situation, depending on the details of each circumstance. In this particular circumstance though, replacement of the deteriorated brick is really the only practical option. By comparison, mortar joint restoration is limited to tuckpointing or repointing. In this case the removal of the partially deteriorated brickwork is a tedious process.
Sounding
Sounding brick or stone masonry, concrete and other cementitious surfaces involves tapping the surface with a hammer in a variety of spots to detect a difference in the resultant sound. Higher pitched sounds indicate a solid integral connection between the surface and the substrate. Lower pitch sounds, by comparison, indicate separation or delamination between the surface and the substrate. As materials begin to deteriorate, delamination can begin under the surface. Delamination, a prerequisite step in the failure which leads to spalling, is essentially the separation of the surface from the substrate.
Brick removal
Brick removal is tedious and difficult work. The process essentially removes or involves removing a hard object pinned in between other hard objects on five of its six sides. People generally think of a brick as having four sides and it does, but it also has a top in bottom surface so in total there are 6 surfaces to the geometric shape of a brick. Only the vertical exterior face is not pinned in between other brick units. One rare exception can be found at an exterior wall corner where two of the six faces are exposed. The vast majority of the wall itself though is composed of brick units that are pinned in or surrounded by other bricks on 5 sides. For this reason, it’s very difficult to remove an individual brick without damaging adjacent bricks. Significant care must be taken in the process of removal.
A few different tools can be used to assist in the process, but none of the tools available, even with all the modern technology we have, really makes the process seamless or easy. One of the best tools to cut through a brick quickly is a cubic zirconia cutting disk. Essentially, This is a metal blade with teeth that are tipped or encrusted in pieces of cubic zirconia. A lot of times it doesn’t look anything like a diamond, but a segment to disk, for example, will have rectangular teeth that are made from a metal looking type substance. This is actually a composite material with cubic zirconia type crystals embedded in the segments at each of the teeth on the wheel or blade. This type of blade is often referred to as a diamond blade.
Another tool that might work well for brick removal is a SDS hammer drill bit. The hammer drill bit itself will make round holes into a masonry, concrete or stone substrate. It can literally make a hole right through a brick, but when working in a restricted area such as within the area of one individual brick, multiple holes can be drilled through or sufficiently into the brick to make it easier to then follow up and demolish the remainder of the brick with a plug chisel or flat head type masonry chisel.
Brick replacement
Once the brick and surrounding mortar have been carefully removed from the opening a new brick can be installed. The installation procedure, in the process of replacement is also complicated because unlike a wall that’s being built from the ground up, in this context the space where the brick will be installed is confined and limited, so there isn’t access to apply mortar in a typical traditional type of manner.
Under these circumstances, it’s best to apply mortor at the back or inside space of the crevice or opening before inserting the new brick. The top and bottom and head sides of the brick can also be buttered or have mortar applied to them before the brick is inserted, but since it’s a relatively tight fit to begin with much of that mortar might be scraped off in the process. Once the brick is set into place, as long as the bed mortar is at the proper height, the other 3 joints, inclusive of the Head joints and the upper bed joint can be inserted in a process similar to pointing. Essentially a tuck pointing tool can be used to tuck mortar deep into the opening. A significant difference between this process and a typical tuck pointing process is that in a typical tuck pointing process the mortar would be installed in lifts, in succession, applying roughly a quarter inch or so of mortar per lift and the total depth of the mortar joint would be less than 1.5″. In this case though, by comparison, the mortar joint depth could be as deep as 3 to 3.5″, similar to pointing. Essentially a tuck pointing tool can be used to tuck mortar deep into the opening.
Proper brick pointing
We discussed the similarities between the brick replacement process and the repointing process, and though they are different, this work itself cannot be done fully or properly without also including additional pointing work. As specific bricks are replaced, they will be removed and new bricks will be installed, one by one, but there are other bricks which have not yet failed and even if they’re determined to be insufficiently good condition, based on the sounding process, those joints at those bricks must also be repointed and properly restored.
There are several key principles at play that must be done properly, with good planning for this overall restoration to be done in good quality to maintain and preserve the wall for generations to come.
Mortar joints at bricks outside of the area of significant deterioration must be removed or raked and pointed to a depth of ¾” to 1.25″. In the image below, you can see some of the exposed remaining mortar joints. Although the joints had held up better than the brick itself, they must be pointed because cracking is apparent and it’s possible that the mortar, in this case, is stronger than the actual brickwork.
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
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- Rubbed bricks
- Rubble stone masonry
- Sand, Builder’s
- Sedimentary rock
- Scratch coat
- Sprung arch
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- 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.
