The tradition of shaping concrete to resemble wood dates back to the nineteenth century. French artisans made faux bois (“fake wood”) garden seats, railings, planters and trellises. Today, you find their work in fine antique shops.
These concrete tree rings draw on that artistic tradition. They make beautiful and durable stepping stones for your garden.
Mix the concrete according to package directions. Follow the manufacturer’s directions to add the brown pigment into the mix.
Do a slump test. A slump test determines whether the concrete is ready for the mould. Concrete that is very wet will pour, literally. A drier, stiffer concrete is easier to work with and will retain the details of the mould better.
Cut off the bottom of the paper cup. Set the cup upside down on a flat surface. Fill it with the wet concrete. As you fill, tap on the side of the cup to remove air bubbles. Lift the cup straight up off the concrete.
If the concrete pile slumps to about three-fourths of the cup’s height, the mix is right to use in a mould. If it slumps more than that, the mix is too wet, so you should add a little more dry concrete mix. If it slumps less than that, the mix is too dry, so add a little water.
Prepare the mould. Spray the inside of the mould with cooking oil. This will help the concrete remove from the mould smoothly when it has dried. Be especially sure to spray details, such as the shape of the “bark” around the edge of the ring.
Fill the mould part way. Tap on the outside of the mould with a hammer in several spots to remove air pockets. Be sure to tap on the bottom as well as the sides.
Fill the mould the rest of the way. Tap to remove air pockets again. The mould should look a little overfull when you are done.
Level the surface. Screed the surface by pulling the 2x4 board across the top of the mould. Move the board back and fourth slightly as you go, to help compress the concrete. If you have a low spot, toss the extra bits of wet concrete into that place and screed the surface again.
Smooth the surface. Let the concrete set until the surface water disappears and the concrete loses its sheen. The time will vary depending on weather conditions. Then smooth the surface with a hand float.
Prepare the pigment mixture. Mix dry charcoal or black pigment, cement, and fine sand in a 1:6:6 ratio. Be sure they are mixed very thoroughly.
Colour the perimeter. Scatter the mixture thoroughly around the perimeter of the form, where the “bark” is located.
Drop a dot of the mixture in the exact centre of the form.
Make the tree rings. Scatter the mixture in concentric circles around the dot. Make some of these “tree rings” are wider than others, as they would be in real wood.
Smooth the surface. Wait for the pigment mixture to moisten from the concrete mix below. Trowel the surface, gently working the charcoal pigment mixture into the concrete.
Create surface texture. Draw the whisk broom across the surface of the concrete in a pattern that replicates saw marks. This will also create a non-slip surface for the stepping stone.
Use a trowel or putty knife to smooth and shape the edges.
Place a polyurethane sheet over the mould to hold in moisture. Leave the concrete in the form in a warm, dry spot for at least three days.
Gently tap the exterior of the mould to loosen the concrete. Remove the concrete tree ring from the mould.
Let the stepping stone continue to cure. The concrete will continue to cure and become stronger for 28 days, so handle it gently at first.
Wear gloves when working with concrete.
Wear a disposable respirator when you mix dry pigment. If you get wet concrete on your skin, wash it off promptly.