Earthbag Building Techniques

Using this simple method and renewable resources, you can build a beautiful bench and arbor for a cozy backyard retreat.
By Owen Geiger
October 29, 2010
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To create a curved bench, set a stake about 56 inches from where you want the front of the bench and tie a string to it. Make a knot in the string 56 inches from the post. As you move the string, the knot makes an arc determining the shape of the bench.
MEEMEE KANYARATH
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Benches and arbors can turn an ordinary space in your yard into a striking focal point. They’re ideal for relaxing and for special, romantic moments. Do you have a quiet area of your yard or garden that could be enhanced with a love seat and arbor? This project is easy to build and can be completed in about three days for about $125.

I tried to make the earthbag bench and arbor affordable, easy to build and easy on the environment. You can use recycled wood for the arbor because it will soon be covered in plants and no one will notice slight imperfections in the wood.

The bench consists of a stone foundation and plastered earthbags, which are polypropylene rice bags filled with gravel.

After you’ve gained experience building this small bench, you’ll be ready to take on larger earthbag building projects, such as the Low-Cost Multipurpose Minibuilding Made With Earthbags.

Arbor Materials

  • 4 8-foot 4-inch-by-4-inch posts (10-feet-long for windy areas)
  • 2 8-foot 2-by-6 beams
  • 5 8-foot 2-by-6 rafters (cut into 1 1/2-inch by 2 5/8-inch pieces)
  • 8 8-foot braces, (2-by-2 or 2-by-4) or wood poles
  • 9 1 inch-by-2 inch-by-12 inch wood stakes
  • 2 to 3 buckets of gravel
  • 50 pounds of cement
  • Cedar or redwood lath
  • Deck screws, brass screws, nails (a handful or less of each)
  • 80-grit sandpaper
  • 2 quarts tung oil, exterior stain or paint

Bench Materials

  • About 2 to 3 wheelbarrows of gravel (with dust or washed — either works)
  • Stone for base, enough to cover an area 18 inches by 55 inches by 6 inches high. The best stone is often flat and about 2 1/2 to 3 inches thick. Two layers of stone this size with mortar between the layers creates a foundation about 6 inches thick.
  • Builder’s lime or cement mortar for stonework: smallest bag available, or use cement from arbor
  • Washed sand (several buckets full)
  • 6 polypropylene rice bags, about 20 inches by 30 inches (when empty)
  • 50-pound bag of builder’s lime or cement plaster
  • Optional cement pigment

Tools

Hammer, string line, shovel, wheelbarrow or buckets, post hole digger or spud bar (a heavy metal bar, usually with a small, wedge-shaped head), circular power saw or handsaw, extension cord, level, tape measure, pencil, paint brush, saber saw, drill, drill bits, screw bit, two ladders, garden hose, flat trowel, brick trowel, hawk or hod (something to hold mortar as you’re working), sponge, optional brick jointer/striker tool for striking masonry joints. If you fill the earthbags with gravel, which is my preference for this project, there’s no need for an earthbag tamper. If you use earth or road base (a special clay/gravel mixture used to build roads), you will need one. Tampers are available from some large building supply centers, or you can build one using the free plans on the Earthbag Building Blog.

Getting Started

The first step is choosing an appropriate site. The ideal spot is somewhat out of the way, not too windy, and with a pleasant view. A cozy site in a flower garden would be ideal. We were fortunate to have just the right-sized space on the side of our yard, but it required adding some backfill to help drain water away. We also added about 4 inches of gravel under the bench to further improve drainage.

Cedar, redwood and cypress are the best woods to use for the arbor, but less expensive wood, such as pine, could be used if sealed or painted. Recycled wood works fine. Using No. 1 redwood heartwood is overkill. Talk to builders who do a lot of remodeling, and they should be able to find what you need. We used 8-foot posts because we get little wind here. If in doubt, spend the extra for 10-foot posts and dig them in deeper.

You only need six woven polypropylene bags, which are used for everything from rice and animal feed to fertilizer. You can find them at feed and ranch supply stores. If you’re really lucky, you’ll find a farmer who has used bags for free. They can be ordered online if necessary.

Also, you need to select stone. Because this is just a small bench, almost any rock would work. Flat, nearly square builder’s stone is the easiest to work with. I made a quick mock-up of the foundation at the landscape supply store by dry stacking them in the approximate shape. This helped me find the best, most uniform stone and determine how much I needed. The stone was a little pricey, so this was a way to cut costs. It helps to have a few extra to choose from as you’re building.

Stone Foundation

Layout the footprint of the bench and arbor. Measure where the posts will go and mark the spots with stakes. The posts are 2 feet apart front to back and 6 feet apart side to side (measured center to center). Measure the diagonals between stakes as well as checking for square using the standard 3:4:5 method. (Check out “Stake Your Ground” in the Do-It-Yourself Pole-Barn Building article for another method of squaring corners.)

You can start with the arbor or the bench. I decided to do the stonework first and allow ample time for it to cure.

Also, you’ll need a stake and string line to define the curvature of the bench. The radius to the front of the bench is 56 inches. Set the stake 56 inches from the place you want the front of the bench to be, tie a string to it and create an arc so the bench is slightly curved instead of simply rectangular. (See photo in the Image Gallery.)

The stonework turned out to be the most enjoyable part for me. I’ve built hundreds of things out of wood but I’m a novice stone builder. Stone is so beautiful and it’s the best, most natural choice for foundations. Sure, it’s a lot of work if you’re building a large project, but anyone can do something this small (less than 10 square feet and only 4 inches high). This part of the project took about 90 minutes.

You may want to have a helper to mix mortar and possibly strike the joints (clean them up so they’re somewhat smooth and excess mortar is removed). Water down the stone the night before and keep it slightly moist for the first few days after mortaring. Dry stone will draw moisture out of the mortar too quickly and weaken it.

I laid the stone directly on 4 inches of gravel. This improved drainage and reduced the risk of moisture problems. I stacked all the stones, using the string line to maintain the curvature, until it looked just right. My stones were flat and uniform, so only two courses created the desired height. The top course overlapped the joints on the first course. Then I carefully removed the top course and set them on the ground next to where they would go. I mixed the mortar, troweled on enough for one stone and then placed one stone at a time. Hold the mortar back from the edge so it doesn’t squish out too much. Repeat the process for the other stones.

All you need is stone around the outside (the perimeter of the bench). The inner space can be filled with gravel. Maintain approximate level, but don’t worry about perfection. The earthbags will shape themselves around the irregularities. The 20-inch wide stone base protrudes about 1 inch all around the earthbags for ease of plastering. This provides a small ledge for the plaster to sit on. You may want to start on the front. This way if the last one or two stones don’t fit perfectly they’ll be hidden in the back. If you desire troweled joints, use a brick jointer to strike the joints. Let the mortar set up a bit before striking. Don’t wait too long or the mortar will crumble away. The most popular shape is a concave joint that helps shed water.

Don’t worry too much about the inside surface because no one will ever see it. After I had the outside looking good, I used the remainder of my mortar to fill gaps on the inside. I threw a tarp over the foundation and misted it occasionally so it stayed damp for the first few days. And, of course, don’t let it freeze until the mortar has cured.

Woodwork

The next major step is cutting, sanding and finishing the wood for the arbor. This entire process took me about six to eight leisurely hours working about two hours at a time. You could stain or paint it after assembly, of course, but it’s much easier with the wood stacked at waist height on sawhorses. Rubber gloves make cleanup a snap.

All the woodwork is straightforward. Rafters are ripped (cut lengthwise) from 8-foot 2-by-6s to eliminate waste. Final rafter size is about 1 1/2 inches by 2 5/8 inches by 48 inches. So if you don’t want to rip boards for the rafters, 2-by-3s (or even 2-by-4s) would work.

Setting the Posts

After all the wood is prepared, it’s time to set the posts. This involves digging post holes, bracing each post with two braces and pouring concrete footings. Check each post for plumb in two directions and use a straight board to make sure the posts are aligned with each other. If you have termite problems like we do, wrapping the base of each post in plastic will prolong the life of the wood.

Some carpenters would set the posts and then cut them to length after the concrete has set. On a small job such as this one, I prefer to spend a few minutes adjusting the depths of the holes to get the tops level. Using this method you don’t have to cut the posts after they’re set. Leave 81 inches above grade. When finished, take a break and let the concrete set up a few days.

Assembling the Arbor

With everything cut to size and prefinished, it’s a breeze to assemble the arbor. All you have to do is drill a few holes and screw the pieces together. Screws are stronger than nails, although you could use nails to attach the lath and rafters.

The first step is to mark and drill the screw holes for the beams. I recommend four sturdy screws per beam, countersunk about half an inch into the wood. Add wood dowels later to hide the screws. Leave a 12-inch overhang on beam ends. Attaching the beams requires two workers on stepladders. Check that all posts are level on top and then attach the beams. The top of the beams should be flush with the top of posts.

Now you’re ready to add the rafters. Wood sizes vary, so you’ll have to work out the exact spacing, but we put them about 9 1/2 inches apart, center to center. I think the rafters look best if they’re placed on edge (with the 2 5/8 inch dimension vertical). They’re also a little stronger this way. Tip: Install a rafter at each end, set up a string line between them and then install the others, aligning them to the string so they’re all straight. One option is adding lath on top of the rafters to create immediate shade. At this point you can remove the braces that were holding the posts in place while the concrete dried.

The next step is adding the trellis. A trellis on each side enables plants to climb up the arbor. You could buy 2-foot sections of prebuilt lattice, a good choice for those in a hurry. I attached small strips of wood with nails and screws in a grid pattern. This method saves money and materials, and only takes a few minutes. First, add horizontal strips 12 inches apart. Cedar lath strips are perfect (quarter inch by 1 1/4 inches or so). Then add three vertical wood strips per side. These can be screwed or nailed on. If you have thin wood, they could be woven between the horizontal strips. The arbor is complete!

Earthbag Bench

Normally, earthbags are filled with soil and then tamped, but gravel is a good choice for this project and no tamping is required. Barbed wire is also used to tie courses of earthbags together in larger projects, but it’s not necessary for the bench. Twenty-inch-wide (empty) earthbags become 18 inches wide when filled with gravel. This leaves a nice 1-inch ledge around the perimeter for plaster.

Filling the bags directly on the stone foundation is easier than filling the bags and moving them to the foundation. For the first row, start at the ends and work toward the center. Fill each bag about two-thirds full, fold the end under and center the bag as you lay it down. You can use a 2-by-4 or your hands and feet to flatten and level the rows. Make two rows, each about 5 to 6 inches thick. Stagger the joints for added strength, i.e., the second row overlaps the joints on the first row. From the photo in the Image Gallery, you can see the bags are not all the same size. The total bench height is about 14 to 15 inches (including the stone base).

Take a few minutes to line everything up so it looks good. Eliminate any large bulges or they’ll cause trouble when plastering. Protruding corners of bags can eliminated by turning bags inside out, or by pulling the corners back and stitching them in place with a nail. Curve the top slightly so water will run off.

Now you’re ready to plaster (stucco) the bench. For larger projects, you would use mesh to keep the plaster in place, but you can plaster directly on the bags for the bench. The ledge on the stone base supports the plaster, making this step much easier. You can use two or three coats of lime plaster, cement plaster or a mix of equal parts lime and cement plaster. Each coat is about a half-inch thick.

Lime plaster mix: 1 part lime to 2 1/2 or 3 parts of clean builder’s sand.
Cement plaster mix: 1 part cement to 3 or 4 parts sand.

Leave a rough texture on the first coat to improve bonding with the finish coat. In some places, the first coat may be thicker than a half inch to fill in the deep spots in the stones. Keep the plaster slightly moist for several days. The plaster will crack if it dries too quickly. Placing a tarp or wet blanket over the top will strengthen the plaster by slowing the drying process. A damp sponge will smooth out any cracks that may develop. You can mix cement pigment in the finish coat to achieve any color you want.

Landscaping

For landscaping around the bench and arbor, choose plants that grow well in your climate. In addition to climbing plants, you can have flowers and other plants around the base. Highly fragrant flowers would be an excellent choice. In keeping with the romance theme of a love seat in a private area, we decided on passion fruit and flowers.

Building Larger Benches With Earthbags

The potential for combining earthbags with privacy walls, planters, retaining walls and so on is nearly unlimited. Not only do earthbag benches provide durable seating, they also add a lot of strength to walls when incorporated into their design. The flexibility of earthbags makes them ideal for curving designs. And because earthbags (sandbags) were designed to hold back flood waters, they hold up in wet conditions. Their only weakness is vulnerability to ultraviolet rays. Try to keep your project covered until plastered. Left uncovered a few weeks during construction won’t cause problems, but it’s always a good idea to plaster as soon as possible.


Contributing editor Owen Geiger is the director of the Geiger Research Institute of Sustainable Building and co-developer of EarthbagBuilding.com. 


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