The information contained in this blog post is for a shorter landscape wall. If you want to build a tall landscape wall, the process will be slightly different. I consider anything five courses or more to be a tall landscape wall. The reason the process is different is that the forces of wind on a tall wall require bracing. You can create bracing with a structural frame, by curving the wall so that it is self supporting, or by adding buttress walls. Buttress walls are short sections of wall that run perpendicular to the main wall. For anything four courses or less, you can use the techniques outlined here.
Foundation Options for a Landscape Wall
The foundation of a landscape wall does not have to be as intense as that of a home. The loads placed on the foundation are just those of the wall itself, including the weight of the plaster. There are no roof loads (unless you add a roof to your design) and no major framing loads; known as dead loads. I have seen foundation systems made of earthbag, stacked stone, and other simple materials. Concrete is the most common foundation material, hands down. Regardless of the material you use, build the foundation the same width as the bales. If you have changes in elevation on your site, step the foundation in intervals equal to a bale height. in other words, if your bales are 14″ tall, make each step in the foundation 14″. This allows you to align the subsequent courses without having to adjust for the foundation steps.
Install Adequate Toe Ups
Be sure to add toe ups to your wall. A simple toe up assembly of a 4×4 on each side of the landscape wall will provide excellent stability for the bales. Toe ups lift the bales off of the concrete and provide a nailing surface for the mesh. You can use a double stack of 2x4s if they are less expensive and more readily available. Lay roofing felt down on top of the concrete to create a capillary barrier between the bales and concrete. Fill the space between the wood members with gravel. This supports the bottom of the bales and provides a further capillary break. Use 20d, hot dipped galvanized nails to secure the bales to the toe ups. As you can see in the photo, they should be nailed in far enough to hold tightly to the toe up, but still need to stick out enough to hold the bales. You’ll drive them into the wood roughly 1″.
The bale stacking process is pretty much the same for a landscape wall as it is for a house. Be sure the bales are flush to the edges of the wall and each other. Make sure the bales are stacked plumb. You don’t want them leaning one way or the other. I prefer to keep all of the “cut side” of the bales facing the same direction. Which direction is not important; however, the cut side of a bale and the folded side perform differently when weed-whacking, so it’s best to keep them facing the same way. You’ll need to retie some bales to make them fit. I use the same knot here as I do on my houses: the Miller’s Knot.
Once your bales are stacked, you’ll need to weed-whack them to clean up the sides. This step really helps to give a solid plaster anchor as it removes the loose straw. Some people skip this step, but I find it both satisfying and important. By removing the loose straw the wall will look sexier and will perform better. And who doesn’t want a sexy landscape wall?!?!
Protect the Landscape Wall from Water
The top of the wall needs to be protected from water intrusion. Some folks will build a roof structure that they place the bales around. This is a great option, but it costs more money, takes more time, and uses more materials. Instead, you can simply install a thick pond liner (EPDM rubber membrane) on the top of the bales and hang it over the sides by a few inches. This will direct water away from the top of the bales and let it drain to the sides. The straw can handle water on the sides of the landscape wall. What you want to avoid is water draining down into the middle of the bales.
In truth, if the bales completely rot away in the next fifty years, it won’t really matter. The straw is not acting as insulation. It is basically just a form for the plaster. Of course, I am not suggesting you build with that intention. Build your wall with the goal of it lasting a lifetime (or three). Just know that if your seal is not perfect, the implications are not as dire as if it were your house.
Plaster Lath for the Landscape Wall
Plaster won’t stick to the rubber membrane on the top of the wall. The membrane’s job is simply to protect the wall from water intrusion. Now you need a way to make your plaster stay put and protect the entire wall from all the elements and pests. I use a plaster-lath cap. Place this over the membrane and use 9″ landscape pins to secure it to the bales. Do your best not to penetrate the membrane. It’s important to create corners that are solid and overlapping with lath. Any lath that doesn’t overlap is likely to cause a structural crack in the plaster. Use a minimum of 1″ overlap. Three inches is better.
Structural Mesh Holds it all in Place
Place 2″ x 2″ welded wire mesh over the top of everything else you’ve installed on the landscape wall. This mesh should be pulled tight and stapled to the toe ups on either side of the wall. Tighten the mesh from both sides at the same time. Pulling one side tight and then the other will make the wall lean to one side. Place even pressure on your tensioning forks so that the wall is pulled straight down. Don’t worry if the wall isn’t perfectly straight at this point. All the pressure of the tensioning might tweak the wall slightly. Use a tamper or a bale persuader to move the wall back into line once all of the mesh is installed.
I use 7/16″ crown x 1-1/2″ staples to secure the mesh. Shoot a staple diagonally across the weld of the mesh every 6″ or so. The mesh should be overlapped by a minimum of 6″ when connecting to the piece next to it. This stops cracks from occurring along that join line. You may find that as you tighten the mesh, the top of the wall gets a slight crown to it. That’s actually great! It will help drain water off of the wall rather than allowing it to sit on a flat wall surface.
Sew the Mesh to the Landscape Wall
The final step is to sew the mesh on an 18″ grid. In other words, place a tie every 18″ both vertically and horizontally. Each tie should be about 9″ long and is sewn on a diagonal to the mesh. this pulls the mesh tight and doesn’t create divots in the wall in the process. Tie the mesh as tight as you can. You should not be able to get a finger between the stitch and the bales. Use the same baling twine to make each stitch. I use a template to cut all my twine to length before I start sewing. This speeds the process up dramatically. It’s also a lot easier to carry a bunch of pre-measured twine lengths than it is to haul the entire roll of twine around with you.
Ready for Plaster
Voila! That’s it. A few more adjustments of the wall with your tamper or persuader and you are ready for plaster. The landscape wall gets the same three coats of plaster as a house would. I use hydraulic lime plaster as it is durable, strong, flexible, and a natural product. (Be sure to tell the folks at the above link that you heard about them through me and they will give you a discount on your order!) If you use earthen plaster, you would need to provide protection from the elements in the form of a roof structure. It simply cannot handle the constant exposure to the elements the way lime can.