How do i make a 15×20 fish pond made out of concrete?
You build a wooden “box” with outside dimensions to match the finished pond plus at least 4 inches deeper. Put it into the hole. Make sure you brace it very well from the inside. Pour the walls and let them set up until solid. Remove the forms and pour the four inch thick bottom. If you also want the outside to be formed you build another box around the first one as far apart as you want the thickness of the walls and brace it from the outside. You would also then need to nail 1X2’s across the tops of the inner and outer forms to keep them from shifting until you are done pouring, then you can remove them to finish the top.
