A few months ago, in the earliest part of the year, still in the late winter, we took a look at a historic stone masonry retaining wall. This wall almost looks like a dry stack wall but it’s not really actually dry stacked stone. Dry stack stone is stone masonry laid together in a wall without the use of mortar or cement.
From a distance this wall looks a bit like a dry stack stone wall. However, dry stack walls are rarely used for large retaining walls of this type.
Dry stack walls, also known as gravity walls, are masonry structures built without the use of mortar or other binding materials. While these walls have been used for centuries in various applications, they are rarely employed for large-scale masonry retaining walls due to several reasons:
- Structural stability: Large retaining walls are subjected to significant lateral earth pressures and loads from the retained soil or other materials. Dry stack walls rely solely on the weight and interlocking of the individual stone or masonry units to resist these forces. Without a bonding agent like mortar, the wall’s ability to transfer stresses and distribute loads is limited, making it less suitable for taller or more substantial retaining structures.
- Resistance to overturning: Dry stack walls have a higher risk of overturning or sliding due to the lack of a rigid connection between the individual units. This issue becomes more pronounced as the height of the wall increases, as the overturning moment caused by the lateral earth pressure also increases. Mortared masonry walls, on the other hand, are more resistant to overturning due to the bond between the units and the added strength provided by the mortar.
- Durability and longevity: Dry stack walls are more susceptible to deterioration and damage over time due to the lack of a binding agent. Environmental factors such as freeze-thaw cycles, water infiltration, and ground movement can cause the individual units to shift or dislodge, compromising the wall’s integrity. Mortared masonry walls are generally more durable and have a longer service life, as the mortar helps to protect the units and maintain the overall structural integrity.
- Construction complexity: Building large dry stack retaining walls can be more challenging and labor-intensive compared to mortared masonry walls. The precise placement and interlocking of the individual units become increasingly difficult as the wall height increases, leading to potential stability issues and increased construction time and costs.
While dry stack walls can be suitable for small-scale landscaping or decorative purposes, the structural limitations and durability concerns make them less desirable for large retaining wall applications. In most cases, reinforced concrete or mortared masonry walls are preferred for their superior strength, stability, and longevity when dealing with substantial earth retention requirements.
Historic masonry construction was mostly done with lime based mortar. Most of the buildings here in Capitol Hill, for example we’re built with brick and lime rich or lime based binder mortar. And like many of those walls here in Washington DC today, they need to be repointed. Repointing is the process of removing deteriorated mortar at the outer edge of the face of the wall between the masonry units. This concept holds true both for stone and for brick masonry.
The picture below shows a different wall from a very close nearby area. If you look closer though you can actually tell there is mortar between the joints and the gaps between the stones of this wall. This wall was repainted more recently and in more recent years. As well, it it is a slightly different type of mortar technique.
The next picture below shows a closer view of the wall from the first picture above, not the second. Here you can actually tell there were mortar joints between this wall at some point in time but so much time has passed and the mortar joints have deteriorate so significantly that now the joints are just filled with loose dirt and even have plants growing between the stones.
Here, as well, from a distance, this wall appears to be a dry stack wall, it was actually a rubble wall laid with traditional lime mortar.
Another closer picture below shows some of the remaining elements of the mortar between the stones. Behind the cobwebs, you can see a dark discolored mortar joint with the binder of the mortar deteriorated and removed from aging over time. Just like historic brick masonry found all around Capitol Hill and Washington DC, this mortar has been in place for many decades and with exposure to weather cycles and unmitigated precipitation, the mortar joints have experienced decades of cycles of excessive hydrated and slowly deteriorated over the years. Like many of the historic brick buildings in Washington DC, this wall is in drastic need of repointing accurate historic restoration.
Tuckpointing, as it’s sometimes erroneously referred to here in DC, and repointing is the laborious process of removing the deteriorated mortar at the outer face of the wall and then replacing that mortar in a sequence step process with historically accurate or mortar that has matching or similar characteristics to the original mortar. There are several different types of masonry units in several different types of wall assemblies and depending on the specific wall assembly, the mortar type and characteristics may vary significantly.
The next picture below shows the same wall from a slightly wider view. You can see both plants and even the plant roots growing in the mortar joints between the stone.
In the upcoming week, we will talk more about alternative types of masonry walls with a similar rubble stone appearance, yet built with totally different types of materials, and we will look at how historic masonry walls like the historic brick buildings of Capitol Hill and Washington DC are preserved and repaired through historic masonry restoration.
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.
In an upcoming article, this coming week, we will discuss some of the elements of restoration and upkeep both on historic brick masonry in restoration processes like repointing, tuckpointing and in restoration and upkeep of other historic elements of both brick and stone masonry.
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 tuck pointing 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.