Discover why brick and mortar are susceptible to water damage
Often, water entry and damage in brick masonry buildings will leave telltale signs that show the pathway, or water trails, of the water movement and the extent of water damage. Sometimes these signs appear in swollen or delaminated plaster, delaminated paint separating from the face of brick or wallboard or plaster attached to the masonry. In other cases, water damage will be apparent in efflorescence, mold, or mildew on the exterior face of the wall,
- Efflorescence is a salt deposit where salts inside of the masonry assembly have been dissolved by water entry and then dry once again after flowing to and reaching the surface of the masonry wall.
- Mold is a fungal growth that generally grows aggressively on carbon based building materials once hydrated, often identifiable from its dark or brilliant colors.
- Mildew is a fungal growth very similar to mold. The easiest distinction between mildew and mold is that mildew is generally white and color whereas mold can be a variety of different colors. Mildew also generally grows flat to the surface or substrate of the affected material where mold, by contrast, grows in colonies that stand away from the flat surface of a material.
The photo below shows an area of a wall where paint is bubbling, indicating significant efflorescence below the surface.
The image below shows A masonry area with mildew or mold build-up on the surface of the brick on the interior of the building. This particular area of deterioration is affected by hydration and water entry from the exterior of the masonry wall. However in this case you can see the example of mildew built up from ingress of water all the way from the outside of the brick assembly to the inside. In this case the brick wall is exposed but in other cases where walls are framed or furred out on the interior side of the masonry partition, water entry can be hidden for a long time, up to years or even decades. In those circumstances, extensive damage can occur from the water entry resulting in rot and more substantial mold growth. Extensive mold growth can lead to biological risk and cause health problems for building inhabitants.
In the same wall in the sections above, the photo below shows another area where the mortar has deteriorated and has fallen out of the brick joints at the exterior surface of the wall.
Signs of water damage are not always direct and clear on a material surface. Sometimes evidence of water damage is hidden from view and where visible it is sometimes not directly correlated with the area of water entry. Often an experienced professional may understand more by looking closely at the leak trails and signs at the surface of ceilings, walls and other building assemblies to discern or analyze the visible evidence of water damage.
Buildings have been built by humans for thousands of years, even over 10,000 years BCE. Civilizations have been building a variety of buildings with very specific shared common functions. Even without contact between these distant peoples, they made buildings for the same reasons, the same purposes, and for these buildings to work, now and then, these buildings must provide these functions. These commonalities exist, even spanning vast disparities of wealth and resources. One of those main building functions is to keep rain, precipitation, and moisture out of the building. Moisture in the form of rain, groundwater seepage or wicking, also known as rising damp and other types of
water entry, causes accelerated deterioration of buildings. This is no surprise, and is obvious to everybody who’s lived in a building. At some point or another, building leaks happen whether it be water intrusion from the outside or escape of liquids from internal piping. These types of leaks are problematic and cause serious damage.
Buildings are strong and made of heavy materials, but they have a few inherent weaknesses. A building’s ability to resist the damaging effects of fire, water, and differential subsoil disabilization is limited. Ingress and water entry can be just as damaging to a building as a natural disaster. Natural disasters happen all at once and are normally very obvious. The deleterious effects of rain and water entry into a building or through masonry though, on the other hand, can be insidious and slow. Sometimes these damaging effects will persist, unnoticed, for months or years at a time.
Brick and mortar are some of the most durable materials. They have a relatively high resistance to ingress and damage from water entry. However, even brick and mortar, one of the best materials to resist moisture, are still susceptible to damage over time. When hydrated residually or routinely from weather patterns, groundwater or rising damp, mortar slowly loses its cohesive elements. In this specific circumstance, modern Portland mortar is different from historic lime based mortars. Modern Portland mortar is better at resisting moisture, but is not perfect. By comparison though lime mortar performs mediocre to resist moisture and will break down over time, especially with residual exposure to significant water entry.
H2O is the world’s most abundant natural solvent. Water dissolves other materials. It breaks them down on a chemical level into their subcomponent materials, separating them on a sub-microscopic level, essentially ungluing materials at their core. This type of deterioration is not disintegration, it is decomposition, moreover insidious below the surface of what is visible and observable to occupants and users of a building and facility. It is particularly insidious because the deterioration can continue and spread without it being noticed.
The image below shows an example of a chimney exposed on the interior of a building. In this case the mortar, on the inside of the chimney, where moisture has come through the brick joints has caused discoloration in the form of mildew on the surface of the brick in the interior face of the building.
The fact that water destroys building materials is basically understood by everyone who ever lived in a building. Most people who are interested or even slightly educated in building sciences know that wood will rot when exposed to water in almost all cases. It’s intuitive and people get this, but not many people understand specifically why or how water deteriorates and damages masonry.
Masonry is somewhat impermeable and partially resistant to moisture. But it still breaks down over time with prolonged exposure to weather cycles and moisture, especially on the interior or interstitial areas of lime based masonry assemblies and especially after initial deterioration. Building material deterioration happens, consistently, in a non-linear manner. In other words, once building materials or a portion of a building such as a distinct building assembly begins to deteriorate, it continues to deteriorate at an increasing rate.
While lime mortar masonry assemblies are still considered a hardy building material, they do deteriorate with prolonged exposure to moisture because mortar wears on the outer face of walls, over years. The exterior face of walls requires tuck pointing on a schedule, every half century or so. Once deterioration begins, it gets worse as it cracks and fractures, resulting in voids, and open crevices form in the face of the walls and in the interstitial area within the brick wythe of the walls.
The photo below shows another example of a void where mortar has to be repointed at the surface of the wall and a void is left behind. Voids like this allow water build-up and allow increased entry of water into the interstitial space of the masonry assembly.
Everything above basically makes sense on an intuitive level because it can be visually observed. But it still doesn’t answer the question of why lime mortar is even susceptible to moisture to begin with. Lime mortar is a combination of several different materials. The largest material in lime mortar is actually silica and not lime itself. Lime is a byproduct or derivative chemical largely constituted of calcium. That is a basic understanding, useful for this discussion but is a gross oversimplification. In the big picture though, calcium and silica make up the majority of the subcomponents in lime mortar. These chemicals alone are relatively stable, In isolation. Lime mortar has a higher permeability than Portland mortar. By comparison, Portland mortar is much newer. Portland mortar or similar type of cements were invented thousands of years ago by the Romans, however Portland mortar has only been used in wide scale production in the United States since about the early 1900’s. Portland based mortars lack the microporosity found in lime mortars.
This distinction makes Portland mortar incompatible with historic, low strength, bricks in circumstances of masonry restoration and tuck pointing.
By comparison, lime mortar is much more susceptible to water damage then its modern Portland. Because of increased porosity, as water moves through the sub surface areas of lime mortar, Those materials naturally dry once more at the surface in the form of complex crystal structures which apply pressure on the adjacent masonry areas, leading to premature failure and deterioration.
In the upcoming discussions we will further examine the tracing of leak trails and moisture entry into brick masonry.
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:
- Water and leak trails
- Delaminated building materials
- Carbon based building materials
- Hydrated and waterlogged building materials
- Furred wall framing
- Rising damp
- Accelerated deterioration
- Escape of liquids
- Portland mortar
- Building sciences
- Tuck pointing
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.