Here is a brief discussion about historic brick and incorrect pointing
This week’s blog article goes into further depth on historic brick-and-mortar compatibility. Historic masonry restoration is a necessary requirement at the vast majority of historic buildings in Capitol hill, Dupont Circle, and Georgetown. The vast majority of these buildings were built over 100 years ago. Those long decades have slowly passed by, and the vast majority of these buildings still stand from that time, but the mortar between each of those bricks has deteriorated.
In previous weeks we have explored several other topics related to historic brick masonry deterioration and restoration. Building rehabilitation and true restoration requires a specialized approach. Far too often similar work is undertaken by cheap developers and flippers, and far too often they cut corners. Improper tuckpointing costs way more than it saves and in recent years prospective homebuyers have begun to become a bit more educated on shortcuts taken by cheap flippers and developers. Below, we take a look at several examples of scam pointing and the use of improper, incompatible mortars. These details serve as a guide for homeowners and commercial building owners alike to learn more and understand the exterior masonry facade of their most valuable investments.
Starting with fundamental basics, it is important to understand that historic bricks were fired, in historic kilns, at a lower temperature than modern bricks (Go to the following link to learn more about historic common bricks.) and they’re therefore softer. Historic bricks also have different constituents subcomponent materials. By comparison, The substrate materials of modern bricks are filtered and sifted using high strength hydraulic equipment. Like equipment. This high Tech equipment did not exist over a 100 years ago. Higher probability and require a compatible mortar. A compatible mortar has characteristics similar to the original mortar and must be a lime mortar. Over a 100 years ago, brick mortar relied on lime as a cohesive binder.
By comparison, lime has very different characteristics than the Portland cement used today. For better or worse, lime has lower compressive strength, higher permeability, Greater expansive qualities, and higher modulus of elasticity. Arguments could easily be made for which is better, between historic or modern mortar but that’s not the real issue. The only thing that matters is that there is compatibility between the brick and the mortar. Historic mortar is compatible with historic bricks.
Modern mortar is NOT compatible with historic bricks and that matters more than anything else.
The adjacent picture shows an example of a historic brick wall which has been pointed in recent years with a non compatible modern mortar. The modern mortar was applied in an absolutely sloppy fashion. The work looks terrible even from several feet away from the wall. That is an instant and obvious indicator that the work was done without professional craftsmanship, but closer observation shows the mortar is not of historic mix and spec and therefore not compatible with the historic bricks of this wall.
The Building Code includes many rules which require proper construction and building techniques, but there are little to no regulations which prevent sloppy work like this and therefore we recommend building owners always hire a trained specialist for tuckpointing and masonry restoration work.
The adjacent picture shows a closer view. The stark contrast is visually apparent between the new mortar and the old deteriorated mortar, even where the paint has flaked off of the deteriorated mortar. The gray color of the new mortar, even though the texture is rough, is indicative of a modern Portland mortar. A true and correct tuck pointing process has not been followed, not only because it is the wrong type and mortar and applied very sloppily but the joints were not raked prior to application. Therefore this is actually an example of scam pointing .
In a very close view below, you can see, not just the stark contrast in color, but you can also see the difference in texture. The historic mortar, even deteriorated to the touch, visually still shows the constituent subcomponent materials, intact but lacking cohesive binder. In this view, you can see the disparity between the 2 types of mortar. The historic mortar is made up of a wider range of constituent sub component materials. The historic mortar, for example, had chunks of lime and had sand granules of greater variation in size. Scam pointing like this, without prepper raking of the joints, saves tons of time and money but is insidious and very harmful to brick walls and in time will cause extreme damage or delaminate.
The adjacent pictures shows a similar condition at a totally different building. In this case, the mortar is actually a lighter color gray, but just at a glance you can see the person (not a professional mason) who applied the mortar wasn’t familiar with working with mortar because they didn’t strike or tool the joints. Striking the joints is the process of tooling or applying it to the surface of the joints to give the joints a relatively uniform surface throughout. Traditional walls were generally struck with a flush mortar joint. In most cases common modern walls will have a bucket handle or a concave style mortar joint which has a bit more of a radius.
In contrast, the picture below shows an example of very sloppy work where the mortar has been applied with some type of tool but it’s just left in a sloppy form and never smoothed or struck with tooling.
The picture below shows another example of improper pointing. In this case a joint at a location and a perpend joint has just had mortar smeared onto the surface. The mortar here is also a light gray color, while visually more similar to lime mortar, yet is still incorrect. This mortar happens to be harder than a historic mortar.
The brick wall below, built with a common bond has soft deteriorated mortar but still shows the constituent’s subcomponent materials clearly, and in this particular example you can see the very large chunks of lime mortar. If a building owner or caretaker is ever not sure whether or not the existing mortar or a newer mortar has lime in the mortar, mortar samples can be taken and simply tested to identify whether or not lime water was used. Lime mortar has a different pH and reacts differently with chemical testing.
The picture below shows the same location as the picture above, but in this closer up view, you can see the very large chunks of lime even more clearly.
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:
- Lime mortar
- Raking, of mortar joints
- Strike, or striking of mortar
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.