forming concrete flatwork
After the aggregate or sand base is rough graded, the perimeter of sidewalk, floor, or pavement must be formed to create a smooth clean edge and to provide a vertical and horizontal guide for the placement of the concrete. The material typically utilized for forms is typically basic 1x or 2x lumber but can also be steel, plastic, flexible composite lumber, or aluminum as well.
The first item of business is to place strings from stake to stake to delineate line and grade of the pavement, walk, or floor. These string lines will take into account any proper slopes as well and will provide the guide needed for form placement.
Once the strings are laid out and the location of the edge forms are known, the forms are placed vertically on top of the grade and steel or wood stakes are driven into the ground directly adjacent to and on the outside of the form. Then nails are driven horizontally through the stakes into the wood providing a firm and structurally sound forming system. Also nails can be driven at a 45 degree angle from above attaching each continuous form together, further strengthening the forming system. The type of nail used is commonly double-headed to allow for easy removal with a hammer. The forms also serve the purpose of providing the correct pre-designed top of concrete elevation for when the screed strikes off the top of the concrete during the placement stage.
Prior to the placement of concrete, edge forms are typically sprayed with an oil based compound which reduces the amount of sticking which takes place between the concrete and the formed surface. After the forms have been installed in the correct position, it is common for the concrete crew to finish grade and final compact the aggregate base. After the forms are installed is the best time to do finish grading as the final elevation for the stone can be pinpointed to maximum accuracy based on the elevations of the adjacent forms.
