WD-40, which is known as water displacement oil, is an effective lubricant and can protect metal surfaces from corrosion. However, if the liquid is used to coat concrete forms, it can create an ugly stain that may be difficult to remove.

A form release agent, which is also referred to as mold release or concrete release, prevents the adhesion of concrete and other materials to a mold or form. It is often applied to a steel or wooden structure, such as a frame or a concrete mold, prior to pouring the concrete. The release agent can be a chemical, oil-based, or water-oil emulsion, or it can be directly applied as an oil-based product.

The best mold release agents are non-toxic, non-flammable, and odorless. They also need to be able to be applied without leaving a residue on the finished concrete surface. Some of the most common commercial release agents are made from petroleum-based products, such as WD-40, while others are made from vegetable or mineral oils.

To make a homemade form release agent, purchase two common oils, such as vegetable oil and mineral oil, that are free of paraffin and other kinds of waxes. Combine equal parts of the two oils in a plastic container. Apply the oil to your concrete mold or form with a paintbrush. Stroke on a medium-to-thick layer all over the inside areas of the form and the top edges. Allow the form to dry completely before using it.