The building of forms to contain concrete is not confined to flat surface areas.  Any area that requires the accurate control and placement of concrete will require forming.  In many areas within a skatepark, these forms will need to follow surfaces that are not flat, but are curved.  Forms can be built to guide a screed across any curved surface.  First, build up a good base of fill dirt and compacted gravel to come as close as possible to the shape wanted.  Decide where to divide the shape so that you will have an upper and lower form for the screed to ride on.  Then, fabricate forms for those dividing lines using ¾-inch plywood.  Cut the plywood fairly close to the shape of the ground.  Then, with the plywood setting at a right angle to the ground, make a fist around a pencil.  With the pencil facing the plywood, drag your knuckles along the ground and trace the shape of the ground onto the plywood.  Cut away the excess material at the bottom of the plywood.  If you repeat this process, by the third time the plywood will conform to the shape of the ground almost exactly.  Make sure that the form is a uniform 4 inches thick (the depth of concrete) by trimming away any excess material from the top.  Stake the form to the ground using the method outlined in forming and flat areas with straight sides.  Use the same method for the other form, if necessary.  Finally fabricate a screed to ride across the upper and lower forms, giving the concrete the desired shape.

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