Concrete formwork is a major investment for a precast or prestress plant. Taking care of the forms extends form life and protects a valuable investment and contributes to a healthy bottom line.
Care of concrete forms needs to be considered every time they are used. Steel form damage can occur with lack of cleaning or with too much use of wire brushes and sandblasting. Vibrators can damage form surfaces.
Proper selection and application of release agents is necessary for lower cost, producing the best product possible and for minimizing form clean up.
There are two types of release agents but they can also be combined for some applications.
The first is the barrier type. They provide a barrier between the concrete and the form. Originally form oils were barrier types of diesel fuel, greases, used motor oil, etc. These produced a good release but lowered product quality by causing bug holes, and staining, resulting in poor product appearance. They hard to apply due to their high viscosity.
The second type of release agent is chemically active and react with lime in the concrete to produce a soap-like film on the form. This type of release agent is the most widely used. Because they are easily applied in a very stable thin film by spraying, wiping, or brushing, you can produce stain-free, void-free concrete surfaces even after the form has been exposed for a day or two. Reactive type release agents applied in a thin film allow the form to strip cleaner which saves on labor costs related to form cleaning and extends the life of the form.
In September of 1999 release agent manufactures and concrete producers were required by the EPA to make and use limited VOC products. Some companies, including Hill and Griffith, saw this coming years in advance and were already producing VOC compliant products. Some states, such as California have stricter rules than that passed nationally.
There are four main application methods-spraying, wiping, mopping or brushing and dipping. Spraying is the most common method of application. Avoid over application to reduce your cost. An extremely thin film of release agent is all that is needed, "The thinner the better." Pump unit sprayers or centralized systems with air pressure regulators give a good consistent pressure and work well. Spray pressures of 35 to 50 psi are best. Higher pressures put more airborne particles in the air throughout the plant and can be harmful to personnel in the plant. Lower pressures cause puddling in the form, and wasted release agent. A flat fan spray nozzle of .1 or .2 gpm will spray a good thin release agent. Many of these thin, chemically active release agents are more expensive per gallon. But with coverage rates at 2000-2500 sq. ft. per gallon the cost is much less than a cheaper barrier release agent. A second type of application is wiping on the release agent. Architectural precasters like wiping the release agent on the form because over application is eliminated. Burial vault manufactures use a sponge for application because they clean the form each time as well. A third type of application is with mop or brush with which over application can be a problem. The mop or brush must be wrung out in order to achieve the desired results. Wipe up puddles. Dipping systems are fast, labor efficient, and assure total coverage of the form. And they collect the excess release agent that drains off the form.
The investment in forms needs to be protected from rust and corrosion, use grease, diesel fuel, or release agent. A better choice is a good rust preventative that offers quality protection, long life, ease of application, and easy removal.
Taking care of forms each time they are used can save thousands of dollars and make a concrete business more profitable.
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