DIRECT CONCRETE TECHNIQUE (Comprehensive)

I developed my method of direct concrete construction to make unique sculptural forms. The advantages of this medium are numerous and the results are immediate, permanent, and durable. Artwork in concrete can be modified and refined throughout its construction. It is also economical and ecologically friendly.

Design

The materials for ferrous-cement, steel and concrete, are heavy so the challenge is to design an artwork that does not look or feel heavy. Steel is far stronger in tensile strength than concrete and thin linear elements in an artwork will look lighter, therefore, design in steel.

Use steel reinforcement bars to physical draw the form in space. Construct a sturdy armature with 3/8" re-bars using three or four rods bundled together with spacers between them for the linear elements and reinforce all joints with braces. Reinforcement bars are easily cut with an abrasive chop saw, reciprocating saw, or acetylene torch. The 3/8" size can be bent into graceful curves in a vice by hand or in a bar bender.

Weld the armature together with an alternating current electric arc welding machine using 1/8 of an inch 1160 flux covered rods. Knock off the burnt flux or slag with a pointed welding hammer and clean the welds a wire brush. Grind off the high spots of weld, splatter, and imbedded slag with a small side grinder equipped with a four-inch abrasive disk. Spray the armature with gray metal primer to prevent it from rusting under the wet concrete.

Wirework

One of the unique things that I do to improve the strength of concrete furniture is to completely cover the armature with galvanized wire in a procedure that I call "wirework". The wire employed is chicken wire and/or hardware cloth, a woven galvanized matrix.

Chicken wire has large hexangular openings and is better suited for curved elements. Because chicken wire openings are one inch or more, use two or three pieces over the same area to cover the armature. Hardware cloth is used for flat areas and at edges where a concentration of wirework is needed. It's available in three sizes, ½ , ¼ , and 1/8 inch open grids. The ¼ inch size is the most useful; however, ½ inch can be used for tabletops because they are cast upside down.

Wrap the armature and attach the wirework with 20-gage wires using needle-nose pliers. Press all of the sharp wire ends inward so that they won't snag on rubber gloves when the concrete is applied. Wirework is a time consuming procedure that takes ten to twenty hours for an average sized piece. It's also hazardous work that can easily result in ragged cuts to hands.

Concrete Mixture

My mixture of "concrete" has no aggregate and is actuality a mortar mix of fine sand and cement. The sand should be so fine that it passes through a window screen. If pea size gravel, which is found in construction sand, is not removed, it will interfere with the ability to make a smooth surface.

I use type 1 or 2 gray Portland cement because it's economical and readily available. If you can find it, white cement is better for accepting the true colors of a pigment. I use coffee cans to measure a dry mix of three parts sand to one part cement. Mix all the dry ingredients that will be needed for the job in an electric cement mixer to ensure consistency.

Wet mix only as much as can be used in less than an hour. A three-gallon pail works best for wet mixing. Add as little water as possible. Stir with a mason's trowel and spray a mist of water in as needed. Use a second pail and transfer the mixture back and forth so there is no dry mix hidden at the bottom. Shake the pail by dropping it a few times to check if any water comes to the surface. If a little water is present sponge it off with paper towels. If the mixture is runny, try to save the mixture by pouring off the water and adding more dry mix.

Application of Concrete

I use my hands, covered with good neoprene gloves, and a small trowel to apply the concrete. Force the concrete through the wirework with a trowel and use fingers to prod, smooth, and pat the concrete so that the voids are filled and the air bubbles forced out. A paintbrush can be used to lightly pat delicate areas and smooth the surface. Blot away any excessive moisture with paper towels. Continue applying concrete until the entire armature is completely covered or must be turned over to get at a section that is upside down. Don't turn the piece over for at least three days. On a modest sized piece, the concrete application may take two or three hours without a break; on a large piece, four or five hours are necessary.

Curing

I cover my hands with good neoprene gloves and use a small trowel to apply the concrete. Force the concrete through the wirework with a trowel and use fingers to prod, smooth, and pat the concrete so that the voids are filled and the air bubbles forced out. A paintbrush can be used to lightly pat delicate areas and smooth the surface. Blot away any excessive moisture with paper towels. Continue applying concrete until the entire armature is completely covered or must be turned over to get at a section that is upside down. Don't turn the piece over for at least three days. On a modest sized piece, the concrete application may take two or three hours without a break; on a large piece, four or five hours are necessary.

Additions, Subtractions and Finishing

After forty-eight hours, the concrete will have set and the surface can be sanded and more concrete added if desired. At this stage the edges are still very weak and could crumble if the piece is moved or treated roughly. With care and common sense much can be done now to improve the piece that otherwise will become more difficult as the concrete hardens. Prepare for the subtractive process by letting the artwork dry out for twenty minutes, so that the wet cement doesn't clog your tools. Wear the appropriate safety equipment, such as a dust mask, goggles and ear protection, when needed. Reduce the high spots with a large wood rasp. Small imperfections and places where wires poke through can be ground out with a small side grinder. Fill gouges, low spots and broken edges with Quikrete® Anchoring Cement. This brand of anchor cement is a powder that comes in a yellow five-pound pail and has instructions for setting bolts in holes. It expands slightly, sets in an hour and is harder than concrete. Anchor cement is somewhat difficult to work with because the working time is only about ten minutes. Mix a few tablespoons of powdered anchor cement with a little water; a spray bottle of water is helpful to get the proportions just right. Apply the mix with an artist palette knife, and after it has set for a few minutes brush the patch smooth with a damp trim brush. To achieve the smooth surfaces that are desirable on furniture it's necessary to sand the entire piece at least five times. Sand with course 50-grit sandpaper between coats of concrete and on the anchor cement patches.

One of the main advantages of working with ferrous-cement is that major modifications can be done at any time. Concrete can be chiseled out back to the armature, parts can be cut off, and more rebar can be welded on. More wirework and concrete can be added to fill out the artwork. The concrete doesn't have to follow the contours of the armature and wirework but can follow what the hand and eye sees fit to do.

Slip and Color

When the high and low spots on the surface are no longer noticeable, the final slip coats can be applied. The slip is the key to making a smooth marble like surface. To make the slip mix silica flour and Portland cement in a ratio of one to one. Add color in the form of powder pigments and acrylic artist paints to water and Quikrete® Concrete Acrylic Fortifier. Use just enough liquid so that the slip can be applied to the piece with a paintbrush. Mist the piece before applying the slip and gently brush the mixture on so that it's thick and even. It's critical to keep the work damp but not runny for the next 24 hours. If it dries out or doesn't set up and flakes off, blast it off with a power washer, sand it down and start over.

After it has cured two or three days sand it with 100-grit sandpaper. For a marble like appearance apply another slip with the same color mixture or a different tint and sand it to reveal the sub-layers of color. Many different coloring effects can be achieved at this stage by painting, marking and splattering pigment on; and sanding, buffing and rubbing the color in or away. Color can also be added to the sealer although it's much harder to alter if it's too opaque. Use Quikrete® Concrete Sealer in a diluted form with water and a little pigment on the first seal to get a more transparent look. Interference acrylic artist paints that contain mica flakes give a shimmering effect to the surface. The last coat of concrete sealer is applied full strength and should completely seal all surfaces so spills and the outdoor weather don't harm the artwork.

Tools & Supplies