The expense of buying rocks to decorate around a backyard pond quickly adds up, but you can cut costs and create your own rocks with cement mixture. The rocks bind together best in the event that you use a mixture that combines cement with an aggregate to make concrete. Rocks can be made in all shapes and sizes, whether you would like to border the edge of the pond with medium-sized stones or create a bigger boulder chair.
Mixing the Concrete
The concrete mix needs to be of a moderate consistency, someplace between thick pancake batter and thin peanut butter. You can mix dry cement, gravel, sand and water at a ratio of roughly 3 parts gravel, 2 parts coarse masonry sand, 1 part dry 1 and cement to 2 parts water. Add the water a bit at a time until you arrive at the correct consistency. Concrete mixes come with the cement, sand and gravel pre-measured and mixed in a bag so all you have to do is add water. As a rule of thumb, it requires 3 quarts of water to mix an 80 pound bag of concrete. Start with 2 quarts of water and put in as much or as little of this last quart to mix the concrete without making it too thin.
Forming the Rocks
Little pond rocks can be formed in sand bed molds. Dig a hole in a bed of sand in the desirable rock shape, fill the hole with the concrete mixture and dig up the finished stone after it hardens. Make medium-sized rocks by bending chicken wire to the desired size and shape and covering it with concrete. You might even use lightweight foam or rubble, like concrete block bits, to start the basic shape and cover it with concrete to finish the design. With the exclusion of this mold method where you pour the concrete, then it’s best to use the concrete with a slinging action so the concrete sticks to itself best. Lay the stone with a chisel and wire brush when it’s partially hardened but still slightly soft.
Leaching the Lime
Cement includes high levels of lime, which can raise pH in the dirt as rainwater leaches the lime to the ground. In case the cement pond rocks are close to the pond edge, lime could float into the water, increasing the pH to dangerous levels. After curing the rocks for a couple weeks, leach them of excess lime prior to placing them in place around the pond. Leave them out in the rain for a couple of weeks in a gravel area where the lime material will not damage surrounding plants. You can even soak them in water for a couple of weeks. Alternately, mix water with white vinegar and then spray it on the rocks to help neutralize the lime, using approximately 1 cup of vinegar per 1 gallon of water.
Coloring the Rocks
Look carefully at any stone and you will notice they have a strong base colour with layers of different colours as a result of the mineral content from the rock. Concrete is gray or blue-gray, therefore tint it with liquid concrete bleach once you mix the concrete if you prefer a different base colour. Dilute acrylic paint with an equal amount of water to paint the rocks. Dip a paintbrush from the paint mix and shake off the excess. Tap the brush against the side of your finger to flick the paint off the brush, leading to vibrant spatters on the stone. Alternate the spatter method with dabbing the stone with a sponge to get a diverse feel. The stone looks more natural as you layer several colours, like colors of red, blue, green, white, black, brown and white.