A good portion of concrete contractors offer cast-in-place concrete work in their lineup of services, whether they're building foundations, single-family homes or commercial buildings. Contractors are typically utilizing either wood panel systems or aluminum forms for residential and light commercial jobs. There are many options to choose from within each forming system, and recent advancements and technologies offer contractors material and time savings.
Plywood forming panels
Contractors use plywood panel formwork on cast-in-place commercial and residential jobs. In the residential sector you'll see a good portion of foundation contractors constructing job-built formwork, while others utilize prefabricated systems with plywood faces and wood or aluminum stringers, or steel or aluminum modular systems skinned with plywood. Plywood is also utilized on all sizes of commercial projects, like office buildings, high-rise structures and parking garages.
Many contractors utilize raw plywood panels, or BB plywood, which is available in a variety of thicknesses and comes oiled and edge-sealed. Industry statistics report that formwork - including materials, labor and finishing - accounts for roughly half of the cost of installed concrete. A growing number of contractors seeking to lower the costs associated with materials, labor and finishing on their projects are choosing to utilize plywood panels that include an overlay of resin-impregnated Kraft paper instead of the raw BB plywood panels. The overlays lend additional features to the panels that help a contractor save time and money.
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The overriding benefit of overlaid plywood is an increased number of pours from each panel. Number of pours varies greatly between the different types of overlays, from manufacturer to manufacturer, and is dependent on how carefully a contractor cares for his panels. There are several types of overlays available, the most common being medium density overlay (MDO), high density overlay (HDO) and phenolic surface film (PSF). Generally speaking, a piece of raw BB plywood will give you up to five pours. With the addition of an MDO a contractor could expect 10 to 15 pours per panel; with an HDO, depending on the manufacturer and application, you will typically get between 25 and 50 pours, and in some cases up to 200. A PSF panel would give you a number of reuses similar to that of an HDO. "Costs do increase with the addition of the overlays," says Lester Pernu, business manager with Dynea Overlays, "but you're still going to save a lot of money on the working side when you can reuse them in your concrete pours."
In addition to the benefits of multiple pours, overlaid panels can offer savings on labor and materials. "An overlaid panel would take far less form release material applied to it, whereas a BB raw wood you would have to oil it fairly heavily and it would absorb much more of the form release, so there would be a savings in the amount of form release agent that you would need to apply to the panels and also a savings in labor to apply the form release to the panels," says Mark Sutherland, sales manager with Ainsworth, a manufacturer of specialty overlaid concrete-forming plywood.
Another added benefit of an overlay system is it imparts a neater finish on the surface of the finished concrete than a BB panel does. "The concrete surface that's left after you strip the panels away from the building or project you're working on with an overlaid panel is going to be much smoother, more uniform in color, and have less grain transfer coming through to the concrete surface," Sutherland says. "There would be less back-end work doing remedial repairs on both the plywood and the concrete surface, which again translates into labor savings."