Choosing the Right Hard Mortar
One of the recurring themes of the information that we provide to our customers here on our website is that they should avoid using hard mortar with soft bricks. We don’t always express it in such direct terms, but it comes out in other ways because essentially it leads the same thing.
Historic bricks are relatively soft, they have a lower density than modern bricks and this is really important because without understanding the difference a lot of times people mistakenly use the wrong type of mortar to repoint and or provide restoration type services to these buildings. A wide range of brick strengths may be acceptable, and as well a wide range of mortar strengths may be acceptable, but it’s about compatibility between the brick and the mortar. These principles come into play in repointing and tuckpointing.
To put things in the really basic and simple terms, the mortar should always have a lower compressive strength than the brickwork. It’s also important for historic mortar to be permeable. Permeability though also is relative. It should be relatively consistent between the brick and the mortar but the mortar should always have higher permeability than the brickwork and as well the mortar should always have lower compressive strength than the bricks themselves.Without these important comparable characteristics in line, it can lead to accelerated deterioration of the brickwork.
The picture below shows an example of where the mortar used had a much higher compressive strength than the adjacent brickwork. The bricks basically disintegrated yet the mortar appears to have remained perfectly intact. It’s simply looks weird and it’s a bad situation.
Eventually, probably years after the construction, the brickwork failed and had significant deterioration in the form of spalling. Spalling is the breakage of the face of the bricks, in most cases due to a incompatibility and lower compressive strength than the adjacent mortar.
In the next picture below, you can see that the mortar joints stand in place, jutting out from the surface of the remaining parts of the brickwork in the wall. A lot of this brickwork has simply crushed or turned to dust. It’s essentially disintegrated.
With typical changes in weather and moisture, micro movements of large and heavy materials are actually relatively common. It’s counterintuitive to think about a large heavy wall moving just because it gets hotter or has more moisture, but it’s actually true, this does happen. These large and heavy elements of buildings will move in a very small micro-movements of just a tiny fraction of a millimeter, but as that movement happens, it happens with immense pressure and force. That force can cause bricks to actually break.
In a close-up picture below, you can draw lots of observations about the characteristics and the components of both the remaining parts of the brick and the adjacent mortar. There’s some mortar which was set directly into the brick work as the bricks were individually placed, one-by-one. One of the trickiest parts of our job, of trying to analyze historic bricks, from a perspective of restoration, is that we need to try to understand what we’re seeing but there’s not always clear signs. It’s important to understand some of the basic principles of historic restoration and repointing and tuckpointing.
In this particular case it looks like the section of the wall may have been built with a portland rich mortar and a historic brick. It doesn’t exactly match, in sequence of time because at the time that historic bricks were being created, portland mortar was not widely available.
This is an example of where analysis can become difficult. It’s possible though that salvaged bricks were used to rebuild a part of this building partition, even after the advent of portland mortar, after it was produced in produced in mass scale. It could have been a salvage brick used to rebuild this wall, at a time a long time ago. We can tell, just from visual observation, that there are several areas of age and deterioration that would have happened since this wall was rebuilt, at the surface of the wall. The mortar appears to be too hard to be fully historic all the way back over 100 years ago.
There’s small pieces of granite type sands in the mortar. You can see these, even from a distance. In the next picture below, I show my finger sticking back into the face of the brick to highlight the difference between the original face and the new face of the brick, it’s over 1.5 in of total depth.
We can Help
Our company focuses on historic restoration more than modern building upkeep, maintenance, and construction, but our company understands both types of construction very well and a full picture well-rounded approach is needed in any niche in the construction industry. Although we focus on historic restoration, repointing, tuckpointing and historic brick repair, our company also has technical knowledge and competencies in the areas of modern and contemporary construction as well as we become one of the leaders in that area of the market today. Understanding both historic and modern or contemporary construction is useful because both aspects help understand the challenges and potential solutions for challenges in building science and construction.
We can help with a variety of historic masonry restoration needs and upkeep, from modest tuckpointing and or repointing to complicated and extensive historic masonry restoration. Infinity Design Solutions is a historic restoration specialist contractor specializing in both historic masonry restoration such as tuckpointing our repointing, and brick repair. If you have questions about the architectural details or facade of your historic building in Washington DC, reach out and say hello and if we can help we’ll be glad to assist you. You can email us or call us on the telephone at the following link: contact us here.
