By Sidney Freedman, Director, Architectural Precast Division, Prestressed Concrete Institute, Chicago, Illinois for a Aberdeen Group Article
The following are a few highlights of the four-page article
"Form release agent must do several jobs:
- Permit clean release of form work 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"
The way a form release agent performs is markedly influenced by the form material. Therefore the release agent should not be chosen until the form material has been selected.
- Wood and plywood forms. For wood forms most of the commercial oils are satisfactory
- Metal forms. Form release agents that are satisfactory on wood are not always suitable for steel forms. Release agents for steel forms should contain a rust inhibitor and be free of water. Materials that have been used successfully include oil or chemically active release agents.
- Fiberglass forms or plastic form liners. These forms and plastic form liners can be used a few times without a release agent because of their hard, smooth finish but after a few uses the surfaces become so rough as to necessitate the use of a release agent.
- Rubber form liners. Most rubber mattings do not require application of release agents if the surface is thoroughly cleaned and moistened with water just before concrete is placed. Some users prefer to coat the rubber with a thin film of vegetable oil
- Plastic foams. Paraffin oil generally is lightly sprayed over plastic foam forms or form liners.
- Concrete forms. Concrete forms, even if they are ground, smoothed and polished, require a release agent to prevent sticking and enable easy stripping. Oils have been used or one or two coats of epoxy resin and then waxed.
- Corrugated cement-asbestos sheets when used as form liners should have an oil-phased emulsion applied as a release agent.
- Fiberboard should be coated with grease having a calcium stearate or aluminum stearate base. Alternatively they can be oiled with a paraffin base oil free of volatile constituents and having a viscosity of not less than 250 Saybolt seconds at 100 degrees F.
- Plaster molds. When plaster waste molds are thoroughly dry, two coats of white shellac should be applied to the mold surface to make it waterproof and nonabsorbent. Before concrete is placed in it, the mold should be lightly greased with a nonstaining soft yellow cup-grease, white petroleum jelly, or a cup-grease that is thinned by adding a mixture of crystallized stearic acid and kerosene to a point where it can be applied with a brush."
Precast Concrete in Google News and NPCA, National Precast Concrete Association
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