OVER THE LAST 16 years, we have developed a new type of trough that is lighter and much less likely to break than hypertufa troughs. We’ve never had one break! These strong “stucco troughs” can have more complex shapes and they can be larger, providing space to create more elaborate rockeries, landscapes and planting schemes that can enchant viewers. They are easier to move about the garden, into your garage for winter plant protection and to garden shows and fairs where they can help attract new members to your NARGS chapter. The stucco trough below measures 36 inches long and 24 inches wide (91 x 61 cm). It weighs 19 pounds (8.6 kg) empty and 157 pounds (71 kg) planted. It’s thin walls free up more space for plants
Stucco troughs are based on the tough synthetic stucco wall technology (EIFS) used in many commercial buildings. A stucco trough consists of a foam core, fiberglass mesh that is glued to both inside and outside surfaces of the foam core with spray adhesive, a thin layer of surface bonding cement that is embedded into and covers the glass mesh and a very thin layer of hypertufa on the visible surfaces of the trough. A stucco trough’s strength is primarily due to the long glass fibers woven into the mesh. A limitation of the thin cement layers is that you can’t have deeply textured walls.
You can build one by yourself, but we like building stucco troughs at our Adirondack Chapter’s workshops where members help one another. Stucco troughs are messy to build and their thin cement layers dry out quickly in the sun, so Mary and I erect an open tent on our lawn with plastic-covered tables underneath. About 20 feet (6 m) from the tent, we place a card table for spraying adhesive, sawhorses for draping drying mesh, and a box fan. We supply a water hose, garbage can, shop-vac, sanding block, wire cutters, ruler, permanent markers, paper towels, two large mixing bowls, and the trough ingredients (listed later in this article) which cost about $16. A cement mixer isn’t needed. Members prepare the foam core before the workshop. Workshops take about four hours if the participants are prepared. First-timers should build a simple rectangular trough and practice the process of wrapping their core with paper and tape.
Step by step building instructions
Step-by-step photos by the author and Kathy Purdy.
A detailed materials list is at the end of the step-by-step instructions.
Prepare the foam core
The easiest foam core is a cut-down styrofoam shipping box. You can reduce the height of your box by cutting it with a serrated knife, hot-wire tool, or saw. It’s easier to apply the mesh later if the cut is straight. Consider what you want to grow before you cut. A deep box will weigh more but is a better growing environment for many plants. A shallow box looks better, like a bonsai container, but will require more frequent watering and will kill some plants faster.
Fill in any depressions in the foam box with Great Stuff Gaps & Cracks spray foam. Mist the box and the spray foam with water to speed its cure rate and give a better texture. Cut off the excess spray foam with a serrated bread knife or saw.
If your shipping box has thick walls (about two inches, 5 cm), you can get considerably more area for plants and rocks by removing a two and half inch (6.35 cm) deep wedge of foam from the top inside edge of your box so that the remaining top edge is 3/4 inches (2 cm) thick. It’ll be easier to wrap this area with the stiff glass mesh if you are careful to make a smooth and even cut as you remove the wedge. Mark guide lines where your cut will enter and exit the foam.
If you can’t find a shipping box with the dimensions that you desire, you can make a rectangular core of any size by gluing together one-inch (2.5 cm) thick extruded foam insulation boards purchased from a building supply store. Use a foam compatible adhesive and push two-inch (5 cm) finishing nails into the joints.
You can make a complex core out of one-inch (2.5 cm) extruded foam and/or commercially available foam shapes with nearly endless design possibilities although some designs will be more difficult to wrap with mesh than others. First, determine your view lines and then draw possible designs on paper. The trough in the photo on the following page is a study in hiding the awkward appearance of tall walls. Views of a twelve-inch (30 cm) high section for growing conifers and daphnes are blocked by eight inch (20 cm) and then five-inch (13 cm) walls. The left side of the twelve-inch (30 cm) high section is cantilevered so that its full height isn’t visible from the front. I was also channeling Frank Lloyd Wright’s house Falling Water. Since surface bonding cement is waterproof, you can build a water garden with narrow rills and deep pools surrounded by plants. You can design a core that reminds you of a favorite building, landscape, cityscape, or garden. Devotees of Lutyens/Jekyll gardens could include a beloved feature from Hestercombe in a trough. At the extreme, troughs can become carved sculptures with planting pockets.
Cut the drain hole(s)
Use a hole saw to cut a drainage hole or holes in the bottom of your foam core. I always use a single two-and-a-half-inch (6.35 mm) hole per section because larger holes are easier to wrap with fiberglass.
Sand the core
Wear old clothes, a hat and a dust mask, and have your shop vac ready. Use 50 grit sandpaper on a sanding block to round off all edges to a minimum radius of a quarter-inch (6.35 cm) so that you can easily wrap them with the glass mesh and the edges will be more resistant to impact damage. This includes the edges of the drain hole(s). Dull any shiny foam surfaces with the sanding block. Vacuum the core and yourself. Place your core in a garbage bag or wrap it with a thin plastic drop cloth to keep it clean and keep it out of the sun. You’ll later use the bag or drop cloth to cure your trough. Your core is now ready for the workshop.
If making the trough at a workshop, you’ll need to bring your prepared foam core, a dust mask, a plastic one-quart or larger bowl, sharp scissors, a misting spray bottle and two wood blocks about four inches (10 cm) shorter than your core.
Wrap the drain hole(s)
Lightly spray adhesive around the drain hole(s). Cut one half inch by six inch (1.27cm x 15.24 cm) strips of the gray self-adhesive fiberglass tape. Insert the tape through the drain hole and, pulling both ends of the tape tightly so that the tape will stretch and lay flat, stick the tape to the hole. Slightly overlapping tape strips, work your way around the hole.
Wrapping the Core with Mesh
These steps are easier to follow if you cut and wrap paper around a cardboard box as you read them. These instructions are for a simple, rectangular core. Discussion of working with more complex cores follows.
1) Prepare the mesh. Cut enough mesh to wrap it across the bottom and sides of your core plus at least eight inches (20 cm) so that the mesh can go over the top edges and onto the internal walls for at least two inches (5 cm). If your core is too large, you can use multiple pieces of mesh, overlapping them by two inches (5 cm). Place your foam core upside down on the spray table. Use a ruler to position the glass mesh over the core. Using a permanent marker, outline the drain hole (mark where there is no curvature from your sanding the edges of the drain hole) and make two reference Xs on both the glass mesh and the underlying foam. The holes in the glass mesh are large enough that a permanent marker easily marks both. Flip the glass mesh over and write “glue” on the mesh. Cut out the outline of the drain hole on the mesh.
2) Apply adhesive. Wearing your mask and nitrile gloves, position yourself upwind of the spray table. Conserve the spray adhesive by placing the glass mesh, with the “glue” side facing you, on top of the inverted core. When you spray the mesh, most of the adhesive will go through the openings in the mesh and hit the core. After spraying the mesh, drape it, glue side up, over a sawhorse. Finish spraying adhesive on the outside of the core.
3) Wait a couple of minutes for the adhesive to partially dry. With a helper, position the mesh, with the “glue” side down, over the inverted core. Align with the hole and the two reference “Xs” and lower the mesh onto the bottom of the core. Press the mesh down with your hands using sweeping motions from the center so that ripples don’t form. If, at any time, the mesh stops sticking well to the foam, spray another coat of glue on both.
4) Starting with your gloved hands on the core’s bottom, press the mesh down the long side walls of the core using a sweeping motion. Don’t allow any ripples to form in the mesh. Flip the core over and continue sticking the mesh to the long vertical walls.
5) Spray adhesive on the wall tops and the interior of the core.
6) At the bottom corners cut narrow fingers in the curved portion of the mesh. Cut enough fingers so that the remaining mesh flaps will lay flat when they are stuck to the core. The width of the fingers depends on the radius of the corner – fingers that are too wide won’t lay flat. The fingers should be three or four inches (7 – 10 cm) long and end on a flat surface, otherwise, the ends tend to stick in the air. Pulling on the end of a finger and keeping it flat on the core surface, stick each finger onto the core. The fingers will cross each other as shown in the photo on page 67. Spray the attached fingers with glue because we will soon be folding more fingers and mesh on top of them.
7) Repeat step six for the top corner above it. After you have folded the top fingers down, fold the flap of mesh (left over from cutting the fingers from the left long vertical side) over them. It’s better to stick down fingers first and then cover them with a flap because it eliminates the possibility of the fingers becoming loose while we’re applying the surface bonding cement.
8) On a rectangular core, repeat steps six and seven on the other outside corners.
9) We’re now ready to fold the long flaps into the interior of the core. Your core’s inside corners may be sharp 90-degree angles or they may be curved if you used a shipping box. You may need to make small cuts or cut additional fingers so that the stiff mesh will lay flat without any bulges on the interior wall of the long side. Using sweeping motions, stick the flap to the long interior wall. Before you press the flap into the vertical corners, check that the mesh will not end on the curved part of the short wall’s top. If it does, cut a strip of mesh off of the top of the flap so that the mesh only lays on a flat surface. Now push the ends of the long flap into the corners and then stick it on the interior of the short wall.
10) Spray the flaps already glued to the internal and external sides of the short walls and stick the remaining two flaps onto the short external walls, over the top, and onto the short internal walls. Again, depending on the shape of the corners, you may need to make some short cuts in the flaps so that they lay flat.
11) At this point, the external bottom, the external walls, and the upper parts of the internal walls have been wrapped with the mesh. The drawing below illustrates how a piece of mesh is cut and folded to fit into a lower internal corner. Cut along the red two-inch (5 cm) long dotted line and fold along the dashed lines. The two lower flaps will overlap each other in the area shaded gray and the mesh will fit into a sharp corner. If the internal corner is curved, then the red line will need to be replaced by a series of two-inch-long (5 cm) fingers.
Cut the four internal corner mesh pieces large enough so that they overlap the external wall flaps and each other by at least two inches (5 cm) so that the internal walls are covered. If there are any gaps left, cover them with overlapping patches that fold down onto the bottom by two inches (5 cm). Stick on a rectangular piece, with the drain hole cut out, to cover the interior bottom.
Wrapping Complex trough cores
I can’t describe all the options for wrapping more complex cores, but I can give you some general rules:
Never end a piece of mesh on a curve.
If a piece of mesh goes over a curve, extend the mesh at least two inches (5 cm) past the curve.
Try to overlap thin fingers of mesh with larger flaps.
Never butt two pieces of mesh together. This would create a weak joint. Always overlap by two inches (5 cm).
Spray the bottom mesh with adhesive before overlapping it with another layer of mesh.
Try to avoid too many layers of mesh. We want to be able to work the surface bonding cement through the layers of mesh and into contact with the foam. Too many layers will get in the way.
Think ahead and practice with paper. For example, if your core has a wall that dead ends into a taller wall at a right angle, you’ll need a piece of mesh that fits like a saddle over the top of the shorter wall. At the curved top of the shorter wall, you’ll have to cut fingers that will spread out on the taller wall. It’s difficult to anticipate all the wrapping challenges you might run into. If you make a mistake, you can always slap another piece of mesh over the gap.
You can’t wrap large sheets of mesh around a sphere, but you can cover it with small overlapping patches of mesh. The patches can be larger if you switch to a lighter weight and stretchier EIFS mesh. You can also wrap a sphere with the FibaTape cement board tape that we use on the drain holes. You can’t wrap very complex shapes like a foam human head (available on the web) but, as long as it isn’t structural, you can spray adhesive on it to serve as a bonding layer and then apply the surface bonding cement and hypertufa without the mesh layer.
Prepare the drainage screen
Cut a piece of quarter inch (6.35 mm) metal hardware cloth rodent screen so that it sets slightly inside the drain hole and a fiberglass insect screen that’s about two inches (5 cm) larger than the hole.
Apply surface bonding cement
At workshops, we mix the surface bonding cement with premixed water and bonding agent in a large mixing bowl. A little cement goes a long way, so we dole it out one pint at a time into member’s smaller bowls. Wearing nitrile gloves, work the surface bonding cement into the mesh using a circular pattern with your fingertips. Start at the drain hole, then the inside of the box, and then the outside. Make sure that the cement is making good contact with the underlying foam. Make sure that you only see the gray of the surface bonding cement with none of the brightly colored mesh showing. I usually do all the box’s surfaces and then go back and apply a second coat of surface bonding cement so that I can’t see any pattern of the mesh. If the cement starts to dry out, mist it lightly with water. If the cement was mixed more than 30 minutes ago, throw it out.
Insert rodent screen
With the trough inverted, jam the metal rodent screen into the drain hole so that its cut wires stick into the foam. Dab some cement where the screen contacts the trough. Place the fiberglass insect screen over the hole and attach it to the bottom with a small amount of surface bonding cement.
Clean out your bowl and fill it with a small amount of hypertufa with bonding agent. Use a swirling pattern with your gloved fingers to apply a thin coat of hypertufa to the visible surfaces of the trough. Use just enough to cover up the cement, the thinner the better. Start with the trough upside down to get to the lower edge and then flip it over and put it on wood blocks to do the rest. On a warm day, the hypertufa can start to dry (not cure) while you’re working, so I hold a water bottle in my left hand and mist the hypertufa when it starts to stiffen. After I’ve covered an area, I’ll pat the surface with my fingers once and then again at a right angle to provide a slightly irregular surface. You could also use a steel trowel for a smooth surface. On an early trough, I applied a thicker layer of hypertufa so that I could have a rough surface. It tripled the weight of the trough and I’ve never done it again.
Cover the trough
Place smaller troughs in plastic bags, and wrap larger troughs with a thin plastic drop cloth. Keep your trough out of the sun.
After one or two days, you can lightly brush the outside of the trough with a plastic brush to give the surface some texture or to remove any glossiness caused by the plastic wrappings. Don’t let the surface dry out!
Keep the trough covered and moist for at least a week. Then you can put it out in the rain to neutralize its alkalinity.
Nitrile Gloves: 5 mil gloves from Harbor Freight work well. You will need four gloves per trough.
A dust mask
A plastic one quart or larger bowl
A misting spray bottle
Spray glue: Be aware that some spray adhesives dissolve foam. We use Loctite Spray Adhesive High Performance 200 Middleweight Bonding High Initial Tack, Wood, Metal, Acrylic, Fabric, Polypropylene & PVC. You can build about two troughs per 13.5 oz can.
EIFS Fiberglass Mesh: Do not use fiberglass cloth that is intended for repairing boats and cars because the cloth does not have an alkali resistive coating. Use 4.5 oz per square standard weight EIFS stucco mesh. It usually comes in 38 inch (96 cm) by 150 foot (46 m) rolls. I’ve never used the self-adhesive mesh that is now available but I plan to try it because it could make trough construction faster and simpler. Available online and at specialty building supply stores. You can make roughly 20 troughs per roll.
Fiberglass Tape: Two-inch (5cm) wide. FibaTape Cement Board Tape, Alkali-resistant. One roll is enough for many troughs.
Hole screen materials: Quarter inch (6.35 mm) hardware cloth and fiberglass insect screen.
Surface bonding cement: I don’t use the standard EIFS base coat because it isn’t rated for below grade use. Instead, I use waterproof and fiber-reinforced surface bonding cement which is stronger than the base coat. I’ve used several different brands and I think that Quikrete Gray Quikwall is the best for troughs. It has a 30 minute working time, so I mix small batches in a bowl. Wear your mask while mixing! Mix with one part acrylic fortifier to two parts water by volume to a toothpaste consistency. You can make about four troughs per 50 pound (23 kg) bag.
Acrylic bonding agent: Use Quikrete Concrete Acrylic Fortifier (No. 8610). Dilute one part fortifier to two parts water by volume. I dilute the acrylic before the workshop so that I can quickly mix it with the surface bonding cement and the hypertufa. A one gallon (3.78 l) bottle is enough for about eight troughs.
Hypertufa: By volume use one part Type 1 Portland cement, one and a half parts fine vermiculite and one and a half parts peat moss sifted through a quarter inch (6.35 mm) screen. Mix with one part acrylic fortifier to two parts water by volume to a toothpaste consistency. Don’t use fibers. I mix up the dry ingredients just before a workshop and then make small batches in a bowl as needed.
Techniques to minimize weight in the planted trough
Foam board crevices
Crevice gardens have been built out of stone, tiles, and concrete. You can also use foam boards. In the trough above, I used two inch (5 cm) thick blue extruded foam board that are two inches (5cm) shorter than their container’s width and spaced apart with one inch (2.5 cm) pink foam. I remove the pink foam spacers as I fill the trough with soil. The blue boards are cut so that their tops are three and a half inches (9 cm) below the surface so that there’s no interference with most root balls. The foam can be easily broken off with pliers if there is any interference. To further lighten one trough, I added two-inch (5 cm) square cubes of foam on top of the blue boards. They were plucked out if they interfered with a plant or a stone. I was initially concerned that carpenter ants would nest in the unprotected foam but that has not happened.
Lightweight soil mix
My trough mix is (by volume) three parts washed sandy gravel consisting mostly of decomposed shale collected about ten feet from the base of a waterfall and sifted through a half-inch (1.27 cm) screen, two parts fine vermiculite, one part forest humus, one half part sifted peat moss and one eighth part sifted compost.
In place of heavy stones, I’ve used driftwood, lava, tufa, and curved stainless steel retaining walls. The steel walls provide interesting level changes with a contemporary feel and take up no space so you can plant more plants. Traditionally, we’ve been told to set stones deeply into the ground so that they will look settled. I look for stones with flat bottoms that I can plant only an inch deep or I cut a stone in half to create a flat bottom. If the stone is then unstable, I’ll drill it and epoxy in a fiberglass dowel to stabilize it.
When working with tufa, I often use many small stones instead of large pieces. I used masonry screws, epoxy, and steel brackets to fasten together a series of small tufa stones to create a retaining wall for the trough pictured at the beginning of this article.