(This weeks post is a review of a technical article by John A Koski, published by the Aberdeen Group and Copyrighted 1994. You can read the article here.)
Enhance the quality and economy of precast products by using the right concrete form release agents
Almost every precaster has had a double tee or an architectural precast panel crack as it was being removed from a form. In some cases, an ineffective or improperly applied release agent may have been the culprit. At other times, the wrong type of release agent may have been used.
(Illustration from a Hill and Griffith presenation about concrete form releases.)
BASICS OF USE
- Make sure the release agent you are using is compatible with the form or mold it is being used on. For example, some release agents can cause an adverse chemical reaction when used on foam or rubber forms.
- When examining prices of comparable release agents, compare them based on their cost per square foot of coverage, not by the cost of a 5-gallon pail or 55-gallon drum.
- Protect form release agents fro m temperature extremes.
- Thoroughly mix or agitate release agents that require mixing or agitating.
- Always use release agents accord-ing to manufacturers’ directions.
- Make sure workers are properly trained in all aspects of the application process.
- For example, some release agents should be applied with a soft, clean cloth. Applying them in some other way, such as with a broom or roller, can greatly diminish the effectiveness of the release agent and lead to unwanted defects in the surface of the finished concrete.
- Do not overapply a release agent, especially when using a release agent that is chemically reactive. These release agents chemically react with the alkali in concrete to form a thin release film.
- If the concrete is to be painted, plastered, or have other coatings applied, be sure to use a release agent that won’t prevent the coating from bonding with the concrete.
TYPES OF RELEASE AGENTS
Oil-based form release agents are composed of vegetable oils, paraffin, fatty acids, and other similar sub-stances.
Polymers can be applied to form a coating that provides anti-stick pro p e r-ties to plywood, metal, and other types of forms. One manufacturer claims 60 to 80 reuses are possible before recoating is required.
VOC-compliant release agents generally are water-based, although some are 100% oil-based. An advantage shared by several VOC-compliant release agents is that they are odor-free and noncombustible, allowing them to be used easily in indoor applications such as precast plants.
Aerosol cans of form release agent also are available. According to one manufacturer, 16-ounce aerosol spray cans can be used on any type of form lining material, including expanded polystyrene foam knockouts, latex liners, fiberglass, and plywood.
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