Unlike the internal lubricants, which are coated from liquid suspension or solution onto a mold or contact surface during the resin processing phase, external release aids are usually applied directly to the resin shape or process equipment by spraying or brushing. Most external release agents are sacrificial and must be applied over and over as the shape is molded and processed.
The choice between powder and liquid will often depend on location and climate, Branum says. Different parts of the country have access to different base elements — fly ash in California, for example — that will affect the final concrete mix as well as the availability and price of the powders used as a release agent.
Liquids also cost more than powders, and they present some unique challenges. They tend to dry out and evaporate more quickly than the concrete as it sets, making them prone to drifting and requiring frequent reapplication. They also have a tendency to streak or stream off slanted surfaces, Branum notes, which can be problematic on a sloped driveway, for example.
When using a powder concrete release, it is important to use sufficient masking to prevent the airborne fine dust from contaminating the work area. The best tool for applying Masters Antique release is a dry tampico brush about 8 inches wide. Load the brush with release by “fluffing” the material up in the pail, then sweep it evenly across the slab to be stamped. It is important to only broadcast enough concrete release to stay a few rows ahead of the stamping mats, Branum advises.