From all the fan mail I’ve been getting these days, I know you’ve been waiting with baited breath for the third blog post in my critically acclaimed ‘Walls’ series. So I’m sure you’ll be disappointed to hear this, but I’m thinking I might take a break from walls after this. Don’t get me wrong, it’s been thrilling- nearly all the jobs we construct include some type of wall, so reviewing all the pros and cons of wall designs and construction has been great. I’ve really enjoyed looking through all our photos of walls and seeing how they define and level spaces, change perspective, increase security and safety, and contribute to the overall aesthetic in a landscape. Next time I’ll switch it up . . . maybe explore the world of yard art or something. But for now, more walls!
Last time I went into the construction of drystack (non-mortared) walls, which are probably the most commonly constructed type of retaining wall in the Bay Area, for their relative speed of installation and low cost. They’re also quite charming. But maybe drystack isn’t for you. Maybe the walls you need are big ones, over 3’ in height, and you know that a drystack wall won’t do the heavy lifting you need. Or you want a smoother appearance to your wall, as even properly constructed drystack walls can have a ‘rustic’ look. (I’ve heard ‘clunky’ to describe drystack as well, but I prefer rustic. It’s friendlier).
Maybe you like stone walls, but the drystack walls you always see around, like those made of Moss Rock or Napa Basalt stone, aren’t turning your wheels. One of my clients recently asked me to design a stone wall for her garden, but with ‘pizzazz.’ She also wanted the wall to be plumb (have a perfectly straight vertical face) which isn’t advisable when drystacking stone. I suggested a mortared stone wall. The material we use is similar in size to the larger stones frequently used for drystack, but by mortaring the stone, we can set it with a perfectly straight face. The mortar is like a glue that holds the stone together, so we don’t need to batter the wall (lean it slightly against a slope) to counteract pressure on the wall.
However, by mortaring a wall, we’re taking away the natural drainage. Drystacked walls can weep water through the joints, but once you fill those joints with mortar, the water needs somewhere to go. So we install a simple drainage system behind the wall to catch water and alleviate pressure. Mortared stone walls may be a bit more complicated than drystacked stone walls, but they’re not as time-consuming as concrete walls with veneers. What are those, you ask?
Have you seen walls that appear to be made out of thin pieces of stacked stone? Maybe you’ve wondered ‘Holy cow! How long does it take to stack all those little pieces of stone and create a solid wall???’ The answer is that it still takes a while, but not because the whole wall is built out of thin stone strips. What you’re seeing is a stone veneer. Veneer is a decorative face that covers a retaining wall. The material that’s doing the work of retaining is typically CMU block (CMU stands for Concrete Masonry Unit, also known as Cinderblock) or poured concrete. These walls can be left as is, and often are in new construction, but a veneer can really change aesthetics and/or hide small flaws in older walls. We’ve done plenty of rehabilitation of old concrete or even old brick walls by applying a veneer. If you’ve inherited walls that you really don’t like, but that are in good shape, a veneer could be the perfect face lift.
The thin pieces of stone on the face of the wall can be Ledgestone, a term that refers to pieces of stone individually mortared to the face of the wall, or can come in premade sheets, for a quick veneer install. Often, a stone cap is laid on the top of the wall to finish the renovation.
Stucco is also a veneer, applied to walls to create a new finish. Stucco can be finished smooth or with texture, have integral color, or be painted after it’s dry. It’s a lower cost option than stone, and takes up far less horizontal space. Further, with so many stucco-finished homes in the Bay Area, it’s often the best choice for the garden landscape as well.
Good old traditional brick is also used as a veneer. Have you ever seen bricks that look like they’ve been sliced in half? Those are likely intended as veneers for concrete walls. Sometimes walls are built completely out of whole brick, but it’s not the commonly used building material it once was, and more often than not, the bricks you see are a veneer on a concrete block wall.
Maybe you’d refer to your style as ‘clean’ or ‘modern’ or ‘contemporary’. A poured-in-place concrete wall could be right for you. These walls are built by forming – creating a template for the concrete – using pressure treated lumber. The forms create the shape, the concrete is poured, and the forms are later removed. The concrete is typically reinforced with rebar for strength. The forms are often made of 2”x 12” pressure treated wood planks, stacked in rows. This leaves a seam in the concrete where one board meets another. Sometimes, this is the only ‘relief’ in a very smooth wall. And people have come to like it: what was once a byproduct of a construction practice that was typically covered up after construction was complete has become a fashionable, desirable detail.
Because of the labor-intensive requirements of building concrete walls, they can get pricey. An alternative for those that want a sleeker wall but a lower cost is a wood wall, built with 2” x 12” planks and regularly spaced vertical posts. In the Bay Area, these walls are typically made out of Pressure Treated Douglas Fir (PTDF) or Redwood. Redwood, though very pest and disease resistant, will start to deteriorate more quickly than PTDF, which is compacted with chemical preservatives to make it appropriate for soil contact. It’s a strong, long lasting material, but not always the most attractive. Therefore, it’s often used behind the scenes. Deck framing and supports nearly always use treated lumber, and only the actual decking you walk on and the railings will be made of untreated wood products.
In wood-based retaining walls, the vertical posts are placed on the front side of the boards, and are bolted through. The posts are set in concrete bases, and drainage is installed between the soil and the wood boards to route water away from the back of the wall and alleviate pressure. Pressure treated lumber is an inexpensive material, so even with the concrete post footings and drainage requirements, their linear foot cost is in the same ballpark as drystacked stone walls. If you want the strength of the treated lumber but a more attractive appearance, a veneer of Redwood boards and/or a Redwood cap can be attached to the face and top of the wall.
I could keep coming up with more wall information, examples and photos, but I think I’ve provided a decent primer on retaining walls you might see in your neighborhood. And I’ve got to go design some much needed walls for a slope in Oakland. So that’s it for now. I hope you’ve enjoyed my breakdown of walls in all their glory. Onward and upward, landscape enthusiasts.