How to Make Concrete Forms in Weird Shapes

You can design and build a concrete form to any shape or size as long as you follow the basic principles of building a standard square or rectangular concrete form. Outside of the odd shape, there is not much difference -- in terms of technique -- between building a square concrete slab or a star-shaped one. As long as you install enough support stakes and footers with your form, you can make it any shape you want. You can even make curved shapes if you have the proper materials.

2-by-12-inch lumber
Measuring tape
Circular saw
Miter saw
Pencil
Nails
Hammer or nail gun
Carpenter's level
2-by-4-inch lumber
Form oil

Instructions

- 1
  Cut down form panels out of 2-by-12-inch lumber, using the dimensions you have for the design of your concrete structure. For long pieces that will be adjoining shorter pieces, make the longer piece 1 to 2 inches longer than the dimension you need to accommodate the joints. For example, a rectangular form with two 30-inch sides and two 46-inch sides would require two 30-inch panels and two 48-inch panels.
- 2
  Cut the ends of lumber at the appropriate angles if you require a form with angles at dimensions outside of 90 degrees. This can be achieved with a miter saw. Mark the longer pieces where the shorter pieces adjoin them to create the angles for your form. Set the pieces up in their basic formation on the prepared build site.
- 3
  Nail the form pieces together. Check that the form is perfectly level with a carpenter's level as you work. When you adjoin a longer piece to a shorter piece, nail through the broad side of the longer piece and into the edge of the shorter piece to create your corners.
- 4
  Repeat this process until all of the form pieces are completely secured to each other. Place a level on each side of the form to check that it is level and make any necessary adjustments.
- 5
  Drive stakes made of 2-by-4-inch lumber along the edges of the form every 2 feet. The stakes should be driven 8 to 12 inches deep, and the tops should end up just below the top of the form. Nail the stakes to the form.
- 6
  Cut footers out of 2-by-4-inch lumber with 45-degree angled ends so you can place them against the support stakes. Drive the bottom ends into the ground slightly, then abut the top angle with the sides of the stakes.
- 7
  Secure the footers to the stakes with nails. Repeat this process until every stake has a footer. Spread form oil over the entire inside surface of the form. Alternatively, motor oil or cooking oil may be used in lieu of form oil.

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