Enhance the quality and economy of precast products by using the right release agent
Article excerpt by John A. Koski published in the Concrete Construction March 1994 issue.
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. Knowing how to properly use form release agents and which agent should be used for a particular application can go a long way toward preventing costly mistakes. In addition, following proper procedures and using the right agent can enhance the quality and economy of a finished precast piece.
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.
- Don’t purchase a release agent based on price alone. 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 from temperature extremes. Release agents that have frozen and then become liquid again may have had their form release properties altered or destroyed. Extremely high temperatures also can damage the properties of release agents.
- Thoroughly mix or agitate release agents that require mixing or agitating. This ensures proper dispersion and continuity of the chemical components within the release agent. Always follow manufacturer recommendations when considering mixing or agitating. Some release agents don’t need to be, or shouldn’t be, mixed or agitated.
- Make sure workers wear respirators, goggles, face shields, gloves, and other protective clothing as required by the manufacturer and government agencies. Make sure workers are properly trained in all aspects of the application process. This includes not only safety concerns, but also how to properly apply the release agent being used. The application technique workers use, however, may not be appropriate for the new product and can cause it to perform unsatisfactorily or not at all.
- Before applying the release agent, remove any buildups of concrete, rust, scale, or dirt that may be on the forms.
- Repair any holes, fractures, or other defects in the forms. Just prior to applying a release agent, make sure that the surfaces of the forms are clean and free of water, dust, dirt, or residues that could be transferred to the surface of the concrete or affect the ability of the release agent to function properly.
- Make sure that forms are coated uniformly with no gaps, sags, runs, or beads. To avoid these problems, never apply a too-heavy coat. Sags, drips, and runs should be removed as recommended by the manufacturer.
- Make sure spray equipment is working properly.
- Do not over-apply a release agent, especially when using a release agent that is chemically reactive.
- On new wooden forms, thoroughly saturate the forms according to manufacturer directions before placing concrete.
- It is best not to wait an excessive amount of time after applying the release agent and before placing concrete as dust and other airborne contaminants can form a light coating over the release agent
- 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.
- Don’t allow release agents to contact reinforcing steel. Doing so can prevent the concrete from bonding to the reinforcement.
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