Excerpt from the February 2020 article from Constro Facilitator
New types of form release agents comply with latest environmental and safety regulations
Release agents are coatings applied on the formwork surface, prior to concreting, in-order to facilitate easy removal the formwork or shuttering. If the appearance of the concrete surface is of significance, it is important that care is taken with the finish surface of the shuttering. Release agents provide the critical barrier between a molding surface and the substrate, facilitating separation of the cured part from the mold. Without such a barrier in place, the substrate would become fused to the mold surface, resulting in difficult clean-up and dramatic loss in production efficiency. Even when a release agent is used, factors such as irregular applications or improper release agent choice may have a dramatic effect on the quality and consistency of the finished product. In the concrete construction industry, form release agents prevent the adhesion of freshly placed concrete to the forming surface, usually plywood, overlaid plywood, steel or aluminum. In this application, there are two types of release agents available: barrier and reactive.
Release agents should have a reasonably long and stable storage life and should not be susceptible to damage from extreme tempera t u re 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 using 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.
Tips on Choosing the form release agent
One valuable standard for evaluation and selection of a release agent is prior experience. However, the safest approach is to evaluate different commercial release agents under actual use conditions, either on a test panel or on a non-architectural portion of the concrete on the project. In addition, information should be obtained from the manufacturer of the release agent about the kind of form surface for which the product is intended and the proper method of application. In making the selection, consider the following:
- Release agent compatibility with the form material or form sealer; that is, whether the release agent softens the plastic from face.
- Final surface requirements. If surfaces are to be plastered or painted, the form contact area should be treated with materials that don’t leave oily or waxy residue that interfere later with adhesion of plaster or paint. Some contractors consider it sufficient to wet the forms with water if surfaces are to be plastered. If the stripped surface is slightly rough the plaster will adhere better.
- Durability of the final surface. The release agent should not cause the concrete surface to soften and dust. Moreover, it should not impede wetting of surfaces that are to be water cured nor should they otherwise hinder the proper functioning of curing compounds
- Discoloration and staining. On forms for architectural concrete, regardless of the kind of concrete finish, a 100-percent non-staining form release agent free from pigments should be used. It will prevent uneven coloring of the concrete. The type of release agent used is of less importance for exposed aggregate concrete because the discoloration usually does not penetrate to any great depth.
- Time period before stripping.
- Environment of the cast concrete.
- Uniformity of performance of the release agent.
Benefits of Releasing Agents
Releasing agents mean coatings which are provided on the formwork surface, before starting of concreting to allow smooth detachment of the formwork or shuttering. Consideration should be given on the finish surface of the shuttering as it reveals all the flaws on the form surface. Some flaws include: vibrating poker known as burns, changeable properties in the form-face material, marks of irregular water absorption in timber. There are several benefits of applying release agents.
- It allows smooth elimination of shuttering.
- Minimizes the occurrence of blowholes.
- Supplys the recommended surface finish for the concrete member cast.
- Minimizes the loss of water from the concrete caused by absorption in timber forms.
- Minimizes seepage of water and moisture throughout curing of concrete.
- Safeguards the formwork and helps in reuse.
- Minimizes the cracks because infernal restraints.
Application of formwork release agents
Release agents should be applied to a clean form before the reinforcement has been placed to reduce the likelihood of inadvertently applying it to the reinforcement. If the release agent does come in contact with reinforcement it should be wiped clean before placing the concrete. When applying a release agent, it is best to follow the manufacturer’s instructions. When too much form release is used, it is not only wasteful and inefficient, but it leads to a number of other associated problems with the finished product. Those who hold the spray wand determine the amount of material applied, so proper training is crucial. The actual cover thickness will depend on the application method and viscosity of the product, which is related to the ambient temperature. Typically, the colder it is in the plant, the thicker, or more viscous, the release agent will be. The warmer the plant, the thinner or less viscous it will be. Different measures can be taken during the application process to account for changes in material temperature throughout the year.
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