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Building Garden Art Using Ferro-cement
by Gerald Klingaman - posted 07/11/11


This garden orb used a wire basket that was used to contain the root system of a shade tree as its armature.


Two of my students in a ferro-cement class I conducted built this nifty turtle.

Garden art is important in every garden but not everyone has the budget to commission pieces in bronze or marble. And, if you have an artistic vision it is not always easy to find just the right piece. But, if you have minimal artistic skill and a bit of perseverance, you can build your own garden additions using a technique called ferro-cement construction. Ferro-cement projects can be built in any shape or size. All it consists of is a steel frame (called an armature) covered with two or more layers of cement. If you have the urge to try this technique, start small to get the hang of it before launching off on a big project. Accompanying this article are several projects I have done.

The first step in building a ferro-cement piece is to construct a steel frame in the form of the object you wish to build using ½- and 3/8-inch steel rebar. The smaller dimension rebar is used whenever a tight bend is needed to frame in the intended shape. Rebar bends easily and I made all bends cold using a conduit bender. Once the frame pieces are assembled they must be attached together. For big pieces, I weld them together. For smaller pieces, the rebar frame can be wired together.

The next step is to cover the frame with stucco lath, available at all big box home stores. Ferro-cement construction is often made with chicken wire to support the concrete matrix, but chicken wire only works if you can get a hand on both sides of the project. Stucco lath comes in 2- by 8-foot sheets, is easy to work with, and provides a stronger support base for the first layer of concrete. It is ideal for pieces where you can only apply the cement to one side of the piece and cannot get one hand on the backside to support the first course of concrete.

The next step is to apply the first coat of concrete. The first coat – called the scratch coat – is a straight blend of 3 parts sand to 1 part Portland cement. This is the basic mortar mix used when laying bricks and can be purchased premixed from Quikrete, but the bagged products are more expensive and you don’t get to play in a sand pile. Ideally the first coat should be applied in the evening and allowed to dry overnight. Don’t worry about making it smooth. A rougher finish will allow for better contact for the final, finish coat. The first coat is usually applied about an inch thick. When finished, most ferro-cement structures are 1 ½ to 2 inches thick.

I use the same cement mix for the second coat but add to it a handful of polyethylene concrete fibers (available from cement ready-mix plants in one pound bags) to each wheelbarrow. Some of the fiber ends will be exposed in the finished project. Singe them off using a small propane hand torch when the concrete is completely dry. Rewet the first coat before applying the finish coat. If you want to use a concrete dye, apply it to the topcoat. I find the brown and beige dyes hold up well, but the reds, blues and greens tend to become chalky looking over time. Acid stains, applied as a spray after the project has cured, do not have the fading problem but are not available in all colors.

The second coat is troweled on or applied by hand, depending on the size of the project. For rounded, smooth forms I usually apply the second coat by hand using plastic gloves, but if your goal is to make simulated bark, then a small hand trowel will be needed. Texture and fine detail can be worked into the surface of the finish coat using a variety of tools such as an old broom, a burlap bag, a crumpled piece of plastic sheeting or assorted screwdrivers and hand trowels. If additional detail is needed and the project is beginning to set up, apply a third or fourth coat as needed to achieve the effect originally envisioned. When completed, cover the project with a sheet of plastic and allow it to cure slowly for a week before moving it.

 

 


This abstract piece stands about 6 feet tall.

 


The armature for the concrete tree at the Botanical Garden of the Ozarks was supported by 4-inch steel tubing, 1-inch and ½-inch rebar, and covered with stucco lath.



The bark texture was applied by using a hand trowel on each shingled bark segment. Acid stain was applied to produce the shading.

 


The finished sculpture was installed in the children's garden at the Botanical Garden of the Ozarks.
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Digital Exclusive. Photo 6 by Jonelle Doughty, myarkansasheart.com.  All other photos courtesy of Gerald Klingaman.

 


Gerald Klingaman, Ph.D., is an emeritus professor of horticulture at the University of Arkansas. He is now working full time as Operations Director at the Botanical Garden of the Ozarks. He gardens in Fayetteville.