Mortar Binder Disintegration & Moisture Wicking

mortar-binder-disintegration (3)If you happen to own a historic building over about 100 years old, you may already be aware that older mortar joints have a tendency to disintegrate and lose their cohesive binder. Essentially the mortar joints crumble on the outside and turn into a loose mixture of sand and particles. The cohesive binder in the original lime mortars appear to be now worthless and defunct.   In most cases though, it’s likely that the mortar on the inside of the approximately 8″ wall, in the case of double wythe construction, or 12″ thick in the cases of a triple wythe wall wall is actually in what may appropriately be considered a still functioning form. Generally, the parts of the wall exposed to moisture and seasonal elements deteriorate faster.

The adjacent image shows an example of a Capitol Hill historic building foyer. This is an interior wall but the historic plaster has been stripped off in years past. The original brick and mortar is exposed and visible, on display as a point of architectural interest.  The brick is in decent shape in most places. There are spots of spalling where bricks were fired unevenly at too low of a temperature, but for the most part the brick is ok and can continue to function in this form without improvement or modification. In another case though, the mortar is loose and sandy and falling out of the wall, literally falling in little ways of dust everything someone walks by. There’s also spots of efflorescence.   The majority of the remaining white spots on the wall are a mixture of efflorescence and historic plaster. The plaster itself is the remnants of a scratch coat made of historic earthen materials including, sand, lime and gypsum.

The picture below shows an example where we took moisture readings across the field area of the wall. We found areas of significantly high moisture.    Moisture can affect a brick wall like this for a variety of reasons. In some cases, such as this particular wall, there could be multiple sources of water entry. In other cases there might be one singular pinpointed area of moisture entry.

The moisture entering this brick construction assembly happened to be coming from particular spots on the outside of the double wythe wall.     In cases where there are  select and specific areas of water entry that can be traced from the inside to the outside, It might actually be an easier issue to repair but even in cases like this we will often recommend wholesale pointing because spot pointing is not effective in the long term.  The wall itself is well beyond the time range in which pointing would be applicable. Spot pointing may save save costs at the specific time of the first repair but more repairs will be needed soon after as other areas continue to age and are already well beyond their recommended service life.

moisture reader

The photos below show other areas where moisture tests were taken.   Across the wall, the amount of moisture entry varied. We happened to find spots that were open or included voids or areas of soft motor. In cases like this where moisture entry can be traced from one side of a wall to the other, the locations of the moisture may not line up perfectly.   Sometimes the moisture will move slightly downward and sometimes at a slanted or offset angle, on the inside of the building. There are even cases where the water or moisture area might be vertically above the area of entry because brick and mortar are permeable and can actually wick moisture upwards,  to an extent.   In other posts on our website we talk about the phenomenon known as rising damp. Rising damp is an example of moisture wicking upwards to damaged parts of brick walls and building materials above the foundation where the water entry happens below grade in or near the below grade stem wall or footing.

The pictures below show examples of testing at the base of the wall. In most cases we would expect to see higher is there moisture levels at the lower area of the wall. That would be a possible sign of rising damp.

mositrure reader

When looking at moisture or water entry, it’s smart to think about building systems in a big picture perspective. In this case we tested the adjacent framed walls as well to verify that moisture levels were not significantly elevated in those areas.

In the image below you can see an up close view of the surface of the brickwork.   There are multiple different types of signs of the conditions just below the surface.   You can see signs of delaminating and loose red clay from the original brick. Bricks like this can be tested by sounding with a hammer and lightly tapping to listen for sounds to indicate the surface of the brick may be susceptible to spailing. Additionally, you can see signs of the original old plaster. You can also see a growth like a fuzz or mildew that is light or white in color. That is not organic growth or mold, its actúa a crystal salt which is a sign of efflorescence. Efflorescence indicates that the brick has been hydrated or had significant moisture over time and has had that moisture pass through the brick assembly and later dry on the surface of the brick. To us this indicates that water is coming into the brick assembly from the outside.

disintegrated brick

From a conservation and preservation perspective, several approaches can be taken to improve conditions related to deteriorating historic masonry and brick mortar joints. Primarily, historic brick and masonry should be inspected and or checked on a routine maintenance schedule, at least annually.   If mortar is kept in good condition, the life of historic buildings can be significantly extended.  Hire a professional contractor which specializes, understands and appreciates historic masonry construction elements and buildings.

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.