Concrete Form Removal Techniques

Timing

• Timing is the most crucial element in formwork removal. If you remove formwork too early, you could ruin the project or jeopardize your own safety. Often, builders reuse their formwork, so it's in their interest to remove it as soon as it's safe to do so -- and to remove it in a way that doesn't break it. Many states have regulations on how soon formwork can be removed, and the Occupational Health and Safety Administration requires that employers test the strength of concrete with an ASTM-approved test method before formwork removal.

Tests

• Sometimes builders use a cast-in-place cylinder method to determine the strength of concrete, where a small amount of the concrete being poured is cast in a cylinder-shaped mold. Its strength is tested to determine whether the batch is appropriately strong. Penetration resistance tests determine the depth reached in the concrete by a steel probe with a force of known magnitude. Pullout tests apply an outward force to a T-shaped metal insert embedded in the concrete surface to determine strength. Finally, the maturity method tracks the temperature of the concrete over time and estimates the strength based on these measurements.

Release Agents

• When making forms, builders often coat form surfaces with chemicals called release agents before placing them. A release agent prevents the form from sticking to the concrete and makes stripping easier. Chemical companies sell specialized form release agents that you can buy at many hardware or home improvement stores. Release agents for wood forms often contain paraffin-based mineral oils and/or oil emulsions. Form release agents for metal forms contain rust inhibitors and are not water-based to avoid damage to the form.

Release Agents

• Fiberglass and plastic forms are much less likely to adhere to wet concrete and therefore do not require release agents unless their surfaces have been roughened by repeated use. Once concrete has sufficiently set, the forms can be "stripped" or removed. The technique for removal depends on the type of form. If the forms are made from wood nailed to supports, the nails can be removed and the formwork carefully pulled away. Metal forms held together by latches can be dismantled.