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Concrete Casting News from the Hill and Griffith Company

Concrete Form Release Agents

Posted by Hill and Griffith Company on Mar 26, 2020 11:10:32 AM

When you’ve chosen the form, you’ve narrowed the choice of release agent

Excerpt from the article in Concrete Construction by Sidney Freedman

A form release agent must do several jobs:
• permit clean release of formwork from the hardened concrete during stripping
• protect the form work for long life and extensive reuse
• help produce a hard, non-powdery, stain-free concrete surface with a minimum number of defects
• prevent corrosion of steel forms and consequent staining of the concrete surface
Form release agents fall into a number of categories, each of which has a distinctive influence on the concrete surface. These are described in detail in the next article in this series. The principles by which they are chosen and the kinds used in various applications will be described later in this article, but first, their handling and application will be discussed.

Site storage

Release agents should have a reasonably long and stable storage life and should not be susceptible to damage from extreme temperature changes or from rough or repeated handling. Care should be taken to ensure that release agents are stored in accordance with the manufacturer’s recommendations, particularly with regard to temperature extremes. Before use, the release agents should be checked for sediment. To ensure uniformity, it may be necessary to stir them adequately. Care must also be taken to ensure that they do not become contaminated. Release agents containing volatile solvents must be stored in airtight containers to prevent a change in concentration. Release agents should not be diluted at the job site unless specifically permitted by the manufacturer. Some oils have a critical emulsifier content and dilution makes the emulsion unstable and causes poor performance.
Concrete Form Release Agents Help Form Removal


The manufacturer’s recommendations on the rate of spread and the method of application should be sought and followed. The optimum rate of spread will depend on both the type of release agent and the surface condition of the formwork.
Form surfaces should be thoroughly cleaned, preferably before erection; forms that are continually reused are generally treated with the form release agent just after stripping and cleaning. Also, whenever possible, the application of the release agent should be so timed that it can dry or be absorbed into the formwork before the reinforcement is installed. This procedure prevents loose rust or dirt from the reinforcement from subsequently showing up as marks on the concrete surface. The release agent should be applied carefully to avoid contacting reinforcement or adjacent construction joints. A few release agents may have their chemical characteristics changed to some extent if directly exposed to strong sunlight for a few hours, and their application may have to be timed accordingly.

Application methods

Any of various application methods can be used, depending on the type of agent. Spray or rolling methods are most commonly used because they are inexpensive and they produce uniform films. When spraying, a low-pressure, fine fog fanning out from the nozzle is most desirable.
Agents can also be applied by brushing, mopping, wiping or dipping, but the first three methods do not produce a sufficiently uniform film. Great care should be taken to see that the wide brushes or soft brooms used for applying the release agent are clean. It is best not to use cleaning solvent on any tools used for applying release agents, but if a solvent is used, care must be taken to ensure that it is completely removed before the tools are reused.
Usually, the dip method of applying release agents is not practical for use on the job site. Therefore, when dipped coatings are required for lumber or plywood, pre-dipping at the mill is the most practical solution. Where a heavy application of an inexpensive coating is allowed, such as where the appearance of the concrete surface is not critical, the roller, mop or broom methods are all applicable. The wiping method is typically used only when very light film applications are required on hard surface form materials or when excess release agents previously applied by other methods must be removed.

Read More

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