Taking Care of Wood Concrete Form Panels
Getting a good return on your forming lumber investment has never been more important. Not only are engineers specifying high-quality finished surfaces more often, your finished work has to be defect-free and meet tighter tolerances. Making sure your crew maintains forming wood to prevent common hardened concrete surface defects such as bugholes and dusting is the key to the success of your business.
Maintaining wooden concrete forms reduces jobsite waste and helps create a final surface that meets the quality specified on the job. It’s important to recognize that defect-free wooden formwork faces are a key component in achieving a finished, quality surface appearance.
Protecting Form PanelsPerhaps the most important maintenance consideration for wooden form panels is the selection of the form release agent. While all formwork should be treated with a release agent prior to concrete placement, no one release agent is ideal for all situations. When properly selected, the combination of coating and release agents will allow easy removal of formwork panels without damaging either the form’s surface or the hardened concrete. It’s important to ensure the release agent does not leave any stain or residue on the concrete.
Other factors to consider when protecting wood forms include the aggregates and chemicals used in the concrete mix. Performance concrete mixes often contain admixtures that aid in the concrete’s workability and set time control. But admixtures often contain chemicals that may lessen a wood form’s service life. Also, many contractors place stiff mixes with high sand content that can cause greater formwork abrasion and wear during placement.
Form maintenance starts with common lumber such as CDX plywood. These untreated woods are often absorbent and should always be treated prior to being placed in service. When selecting treatments, be sure to select a coating designed for wood. Plywood form coatings, such as lacquers, resin, or plastic-base compounds and similar field coatings sometimes are used to form a hard, dry, water-resistant film on plywood forms. The first coating should take place at least 36 hours prior to placement. A second coating treatment should occur prior to each placement. In most cases the need for application of a release agent between pours is reduced by the field-applied coatings.
But when using engineered wood panels, the selection process for coatings and release agents requires more attention. These panels have been pretreated at the factory and are designed to repel water and seal edges. It’s important to follow the manufacturer’s instruction on release agents.
For these products, most manufacturers suggest choosing from two main categories of release agents.
Barrier CompoundsBarrier compounds form a physical barrier between the concrete and formwork to provide release. Their formulations commonly include water-based or solvent-based petroleum products; paraffin-based materials; or soap-type release agents. These materials leave a film that separates fresh concrete from the panel’s surface. Unless routinely cleaned, layers of the “film” tend to build up on the form surface.
Chemically ReactiveChemically reactive concrete form release agents are formulated differently. They contain a small percentage of fatty acids, often a vegetable oil, or more commonly, a petroleum-based ingredient. Both materials combine with the calcium hydroxide in fresh concrete. This reaction creates a metallic, waterproof soap which prevents concrete adhering to the form. This soap substance forms a barrier between the face and the fresh concrete. Its advantage is that it doesn’t leave a residue following stripping. Forms treated with these products often require less cleaning between uses
Maintenance Procedures for FormsFormwork should be handled with the same attention and care as tools. By adopting some important procedures contractors can increase the service life of wooden formwork and cast quality surfaces.
- Prior to the forming process, workers may need to cut plywood panels to achieve the designed shape. Following each cut, workers should reseal the form’s ends and edges. This simple step prevents moisture intrusion and possible swelling.
- Depending on the wood type, workers might need to lightly sand the form’s face to remove any excess oil, dirt, or dew.
- Protect the panel during storage. It’s best to stack panels face to face to protect the cleaned surfaces, corners, and edges.
- And this is the proper time to pre-order the recommended combination of materials for coating the form’s face and the release agents that will be used on the next job.
Handle wood formwork with care. Ensure panels aren’t dropped by using proper lifting and handling procedures. And pay close attention to how the panel joints are moved into their final position by protecting corners and edges.
Applying form oil just prior to placement is an important maintenance practice. The amount of form oil should be determined based on the choice of coatings and treatments. Remember this important rule: “Less is better than more.” On most applications, the thickness of the form oil is often only 0.005 inches. If the release agent is too thick, there’s a chance that the surface of your hardened concrete may be discolored.
Contractors need to recognize that this process is an art, as there are variables in determining the best performing thickness on a given day. These variables include the type of formwork lumber, the design texture, the viscosity of the product and the jobsite’s ambient temperature. Monitoring the sprayer’s nozzle condition and spray pattern is also important. (When pouring in cold weather, try to determine if the forms will be heated prior to placement.)
Avoid overloading forms during placement. By observing the pour rate specs for your specific type of forms, there’s little chance of warping and damage.
Monitor the use of internal vibrators near the formwork surface. Vibrator burn will mar the concrete surface and reduce panel life.
Removing Your Forms
It’s important to carefully remove forms when the concrete is effectively hardened. To protect both the form’s face and exposed concrete surface, workers should use wooden wedges. In most instances, the form will separate from the concrete with a slight tap on the wedge. If for some reason the form doesn’t “pop” away, try adding additional wedges rather than striking the original wedge with too much force. It’s also important to be sure the wedge surfaces are smooth.
- If you find residual concrete on your form’s faces, carefully remove the concrete as quickly as possible to prevent any further bonding.
- Forms should be cleaned immediately after stripping
- They then should be solid-stacked or stacked in small packages, with faces together. This slows the drying rate and minimizes face checking.
- After removal, try to place the forms in a dry location. This will allow any moisture that may have entered the form to dry.
Inspection And Repair
- Before reusing each form, inspect the face. Look for any damage from nails, release agents, or vibrator contact. Refer to the formwork manufacturer instructions for the type of patching material to be used. There are also kits that include round plugs that are designed to repair drilled holes for connectors.
- If there is any excess concrete on the form, use plastic tooling to carefully remove the mortar.