Understanding Fake Rubble Masonry Walls: An Overview
Retaining walls are commonly used for stabilization at grade changes in general site layouts and yards. However, this type of masonry can also be seen at many building foundations and facades as well. We first looked at a attached building assembly next to this particular retaining wall this past winter. Some of the photos from that initial site visit follow below and today will look at those images and talk about some of the implications of the material used for this type of building structure and the architectural aesthetic elements as well.
The exterior face of the wall looks a lot like historic real stone construction. It’s not actually stone though and it isn’t even built with individual masonry units, its fake. The wall is actually built with concrete.
The pattern seems to be somewhat random there’s even different color pigments applied to the stone facing so it looks very much like an actual stone construction.
When you look very closely though, you can see that beyond the applied pigment at the outer face of the concrete wall, you can actually see a consistent light gray color concrete in the joint areas. If it were actually built with stone and mortar than the gray color at that location, coincident with the ostensible location of the mortar joints. You can see the real difference though when you look closer, there are small voids in the face of what is made to room like a rounded river rock. These small round shaped voids are made from the air bubbles in the wet concrete, at the time that the form was filled with the freshly mixed concrete. Concrete normally has some air mixed in and generally concrete can be vibrated to have the air bubbles float to the surface of the concrete to avoid voids or omissions inside of the concrete itself.
The next picture below shows an angle of the wall, looking at it head on, at this angle you can see the area between the stones more clearly where water would typically be installed. If you follow the curve of each of the stones, it looks as if they make an almost precise fit from one to the next without any real space for an actual mortar joint. Real stone walls are not built in that same way unless they are a dry stack, but round river rocks are rarely ever used in dry stack construction.
Rounded river rocks lack inherent interlocking surface. As an analogy, imagine stacking a square box on top of another square box, it’s easy to do, they would basically sit in a stable way, on top.of one another. In the same way, imagine stacking a round beach ball on top of another round beach ball. The beach ball doesn’t have a tendency to stay put on top of another beach ball, it would just roll off. The same principles apply to stone masonry. A smooth, rounded surface prevents them from naturally locking together, which is required for any stability of a dry stack masonry wall.
Dry stack construction is done without mortar and in this type of construction, stones must have irregular oflr flat edges that fit relatively tightly with one another to create friction and mechanical interlock. Rounded river rocks, by contrast, tend to shift or slide over time due to their smooth contours, leading to instability, especially under load or in dynamic environments such as areas with freeze-thaw cycles.
The lack of flat surfaces makes it difficult to achieve consistent contact between stones, which is crucial for distributing weight and pressure evenly throughout the wall. This uneven load distribution can cause points of stress, leading to localized failure. For these reasons, more angular stones, such as those with split faces or rough surfaces, are preferred in dry stack construction, as they provide better structural integrity without the need for mortar or adhesives.
Rounded river rocks can sort of also create a lack of visual interest in dry stack walls. They are more uniform, generally and can have less visual appeal compared to the varied textures and shapes of more traditional masonry materials,
The pictures below show an example of a wall that’s basically a hybrid or in the middle of the typical categories of rectilinear ashlar masonry and rounded rubble masonry. The lower portion of the wall has been reported in more recent years and decades but the upper portion of the wall looks as if it’s completely a dry stack wall with no mortar.
When you look very closely though you can see there’s actually mortar between the stones, in most cases though that mortar is significantly deteriorated. At this point with this high level of deterioration, the motor looks a lot like dirt and has even become a breeding ground for biocolonization and plant growth.
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.
