Should mortar be used for dry stack retaining walls?
Sierra team just wrapped up this freestanding dry stone wall in Hardwick, NJ
Building with stones is the world's oldest known construction method. It even surprised me to learn that the oldest known building, still standing, dates back to 3600 BC. The Knap of Howar resides in Papa Westray, Scotland. What most may not have also considered is that this home was built without any sort of binding substrate such as cement, concrete and mortar. Similarly, you can find remains of extremely old structures around the world built in a similar method. This method is called Dry Stone.
What is Dry Stone? Dry Stone is the method of building with stones in a manner which uses no additional binders such as concrete, mortar, clay, etc. This construction method relies on the interlock and weight of the stones to keep things in place. Today, buildings are not often built using dry stone methods. In the landscape space this technique is still alive and well, though frequently challenged by masonry and concrete variants. There are several disadvantages to dry stone construction, though there are also many advantages as well. Let's look at what's going on so you may know which is right for you when selecting a landscape contractor for the stacked retaining wall for your outdoor living project.
First, let's have a look as to why dry stone is less popular today and often assisted or even replaced entirely by mortared walls.
Speed and Cost - Let's keep it real simple. Time is money when it comes to construction. Using mortar to put together a stacked stone retaining wall saves the pain staking task of installing what is known as the "hearting". The hearting is the infill of the wall system. The smaller pieces installed in a manner which interlock the stones together causing them to be able to withstand the forces that will be applied on them. Mortar under and behind these stones allows for a less skilled and faster installation.
Skill - The reality is that there are very few professionally trained dry stone installers in the world. In certain locales it is making a comeback as more of a heritage art form, and in certain regions of the world it is more prevalent than others. Finding a stonesmith that understands true dry stone methods and will be able to build a structure that stands the test of time is no easy task. By default, many resort to non dry stone methods because of lack of having the right team and in some cases just not having the knowledge.
Misconception - We often hear the debate of which is better dry stone vs wet laid. In just about every instance the debate is weighted by a perception of what dry stone is, based upon personal experience. Unfortunately, when many think of a dry stacked retaining wall they might also think of a wall falling over, leaning, or needing an expensive rebuild. Rest assured the stone is not to blame in most of these situations. Most commonly these visions are the result of being witness to a stone structure which did not adhere to the simple yet often unknown rules of dry stone construction. Let's have a look at those real quick.
Rules for lasting dry stone structures:
Base Prep - Just like all other construction methods, the first step and the one that often makes the biggest impact over the long term is the foundation. Base prep will vary based upon soil conditions and regions, though the end result is the same. You want your base layer of stone to be stable and not move around over time. In the New Jersey climate we prefer to use clean gravel that is compacted as the substrate below our base layer of stone.
Size Matters - Larger pieces on the bottom, smaller on the top. The larger the structure the more weight will be applied on the bottom stones. Larger stones at the lower levels will be more efficient at transferring the weight applied and make for a stronger structure.
Interlock, Interlock, Interlock - The most crucial part of dry stone construction is the stone to stone interlock. The same holds true for most building materials. The number one reason we see stacked stone and boulder walls fail is because of a lack of interlock with the stones. It might be easier to stack them vertically, but it is never as strong. Generally speaking you always want to bridge the joint of 2 stones with one stone not just on the face but in the wall insides as well.
The Guts - What you do not see is critical in the long term success of your structure. The hearting is a critical and pain staking process where the voids in and around each stone are filled with intentionally placed smaller pieces to interlock the stones together. This is a very time consuming process, and if not done well will have a noticeable affect on the end result. We sometimes see gravel being used to cheat this step, but it is no substitute. If that gravel somehow gets between the stones you have introduces a potential point of failure by reducing interlock and friction.
This all sounds hard and complicated...why should I use dry stone methods?
You Like a Challenge - OK maybe not a pro for most, but this possibly is why many including myself are drawn to the world of dry stone.
Heirloom Grade - All said and done, when comparing a properly built dry stone structure and a properly built concrete structure who will win? The answer will always be dry stone. I'm going to hear feedback on this one, but I haven't ever heard of someone traveling around the world to see the world's oldest mortared structures. See where I'm going with this?
Curb Appeal - To those that see the difference, there is just something about a dry stone structure that is appealing. An appreciation for the time and skill that went into crafting the result. The color, the style, the unique result that only a specific stonesmith can provide.
Habitat - Perhaps not something that might be appealing to all, but dry stone walls also serve as a habitat for small animals. The impenetrable walls make them a safe haven for lizards, chipmunks and sometimes the slithery predators that keep less desirable animals away.
Is dry stone more expensive?
This is a really great question. The answer is it might be. There is a lot to be considered such as access to the area, preexisting conditions and the actual design. You can find out more about different retaining walls and overall costs for outdoor living construction in these articles below.
Click Here: Retaining Wall Cost Comparison
Click Here: Outdoor Living Buying Guide
At Sierra Landscape Management LLC, we create heirloom grade outdoor living environments that draw deep inspiration from nature. We aim to bring a little nature closer to each property we are privileged to work on. We believe in sustainable and lasting approaches which provide special places for our clients and their friends and family to enjoy life and make memories. If you would like to learn more about how we can create a nature inspired outdoor environment for you and your family please reach out to us by using the button below.
Thanks for reading!