How to Cast Window Surrounds

Place the molds for your window surround pieces on a sheet of 3/4-inch plywood spacing, them about 4 inches apart.

Create the concrete mix for the surrounds in a large bucket. Measure out 750ml of white sand with a measuring cup and pour it into a large bucket. Pour the same amount of portland cement into the bucket along with the sand. Stir the two materials together thoroughly with a wooden stir stick. Add 40ml of the polypropylene fibers to the mix for additional support of the concrete. Stir the fibers in well with the other two.

Combine 200ml of water with 100ml of liquid latex in a second bucket. Mix thoroughly until there is no sign of the separate materials.

Add the liquid slowly into the bucket containing the sand, cement and fiber mix. Combine all of the materials together using an electric drill with a mixing attachment as you mix in the liquid. Add enough liquid to create a concrete mix that’s the same consistency as oatmeal. Once you have the proper consistency, stop adding the liquid and continue to mix the concrete for three more minutes.

Spray the molds with a mold release agent to prevent the concrete from binding to the mold or leaching out moisture, making it brittle.

Fill the molds with the concrete mix, pouring it in at a corner of the mold and allowing the concrete to flow throughout.

Tap the plywood around the sides of the molds lightly with a rubber mallet to help settle the concrete into any voids in the molds and to force any air bubbles to the surface.

Allow the molds to cure for seven days, then remove the surrounds from the mold bodies. Stack the window surrounds in a cool dry place and let them cure for another 14 days before installing them along the sides of your window.