Acceleration humps, pump-humps or bumps are essentially smooth mounds of concrete placed within the skatepark to be used as free standing obstacles.  A saddle is a smooth mound of concrete that typically is a transition between two bowls or between a bowl and another series of elements within a skatepark.  The quickest and easiest way to build this type of obstacle is to simply place earth and gravel in the area where the obstacle is desired.  Then compact the earth and build a lower form around the substrate as outlined in forming straight and curved areas.  The concrete can then be placed within the form to the desired thickness and the surface floated and finished free-hand.  However, smoothing large surface areas accurately without a screed is difficult.  If you have a large area, the best you can hope for is fair results. 

The most accurate method for forming acceleration humps and similar obstacles is to place earth and gravel where the obstacle is desired, and then wet and compact this substrate.  After that, divide the obstacle into at least two pieces across the top of the mound, at the highest point.  With the division of the mound determined, an upper and lower form can be built using the methods outlined for forming straight and curved surfaces, and forming across radii and curved surfaces.  With the form in place, fabricate a screed to ride on the upper and lower forms using ¾-inch plywood. 

Fabricating the screed to the correct shape is easy.  Cut the plywood close to the shape of the substrate.  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.  Attach pieces of wood to the top and bottom of the plywood shape to ride along the upper form (or coping) and lower form, and also serve as handles.  Make sure that there is a radius at the bottom of the screed where the obstacle meets the surrounding area or the obstacle will have a “kink.”  Check to confirm that the screed will also create a fluid curve at the top of the obstacle.  Perform a test run with the screed before using it to place concrete.  Place and finish the concrete on one side of the obstacle first.  Then remove the upper form and place and finish the second side, using the previously placed concrete as the upper form.

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