“Masonry is an art form. Creating stonework is like putting a puzzle together without a picture.” ~Jason the Mason
Gravity retaining walls have been built since ancient times because they are functional and beautiful additions to any landscape. Whether gravity walls are made of stone or concrete, the basic principle behind them is simple: gravity pulls the heavy stones down, and this weight provides stability and retains the soil behind the wall. When you decide to build your wall, it’s important to do it right. In this post, we will go step-by-step through the process of building a gravity retaining wall the right way.
But first, as we mentioned in our last blog, “Garden Walls Done Right,” there are five things to consider before deciding what kind of wall you want to build:
- Existing condition of soil.
- What will be above the wall (a driveway? A house?).
- The slope above the wall.
Once you decide on your budget, consider what style you want your wall to have. If you are looking for a more formal feel, stay tuned for our next blog on concrete gravity retaining walls. But if you are looking for a more natural look, consider using stone.
Below, we describe how we did one of our favorite stone gravity wall projects. We used boulders that weighed over one ton to create a unique, natural look without any repetitious pattern. This was a big job in every way, and it illustrates the importance of using the proper equipment, materials, and professional expertise. Here’s how we did it:
Step 1: Get the right tools for the job.
Having the right tools can make all the difference. For instance, we use an excavator with a hydraulic thumb to move stones around. A cool feature of excavators is that you can add attachments to the hydraulic arm. We attached a bucket to make it a lot easier to dig footers.
A key tool for ensuring strong walls is a plate compactor. This device uses a vibrating, flat plate on its underside to .compact loose soil so the wall’s foundation is rock solid. Other go-to tools are a concrete mixer and a gas-powered chop saw with a 14-inch diamond blade.
Step 2: Prep the soil.
Once you’ve got your tools, the next step is preparing the ground beneath your wall. For your structure to be sound, you’ll have to build on virgin soil. Keep in mind that the virgin soil you’re looking for probably is covered by duff. Duff is a layer of softer soil that’s been created over many years by the slow decomposition of organic materials, such as pine needles, twigs, and leaves. You have to remove the duff layer to reveal the virgin soil underneath. For this project we had to dig down about 2 feet to find virgin soil.
Step 3: Dig the footers.
Looks won’t get you far if your wall keeps slipping in the rain! That’s why footers are so important: they provide a stable foundation and a level surface for the bottom of your wall.
For this job we dug footers about 6 inches to 8 inches deep with our excavator. We then added gravel and compacted it.
Depending on the size of your job, you may need an engineer to tell you how deep are the footers you need and where they should go.
Step 4: Laying your first row.
Once the footers are ready, it’s finally time to start placing stones. Gravity retaining walls have large bases. The stones lean back on each other to stay balanced and retain the soil correctly. So make sure you pick larger, wider stones for the first layers of your wall. Arrange the first row of stones in a way that provides support and is aesthetically pleasing. Your wall will begin to take shape.
Step 5: Drainage
Now that the base of your wall is secure, you have to ensure that it can bear the weight of the soil behind it plus the additional pressure that will come from water during a heavy rain. During a rainstorm, the water will try to escape your wall through the point of least resistance, so it is very important to create a drainage system that allows for large amounts of water to be dispersed quickly. Before placing any more rows on top of your first layer of stone, begin adding drainage. Gravel can be used to strain water and help it disperse towards the bottom where a drain pipe can take it off site to a safer location. Adding gravel and piping behind the base layer will channel the water flow so it doesn’t push against your new wall.
After putting some of the drainage down, we add mortar to the back of the stones to ensure that soil will not seep through.
Step 6: Add layers of stone.
Now the process just keeps getting easier. Basically, you start adding stones to the wall to increase its height. Then you mortar the cracks and add more gravel. Just continue this process until you reach your desired height. When stacking your stones, remember that you are creating a work of art. Place stones in a random pattern; you’ll have a beautiful and stable wall when you make sure that the lines between stones don’t line up with the lines on the row below.
Step 7: Plant flowers and voila!
All that is left for you to do now is to create a space that suits you by adding furniture, plants, and other items you like. VOILA! You have created a personalized space that is practical, safe, and beautiful.
When you’re ready to build a retaining wall, contact the experts at Art of Stone.
Look at the photographs below to see more of our progress.