construction

Step-by-Step

Sidewall forms are basically plywood-faced 2x4 stud walls. Working on a flat surface, nail the 2x4 frame together with two 16-penny common nails or 3-inch screws at each joint. Fasten the plywood sheathing around the perimeter with a few 8-penny nails or 2-inch screws. Coat the inside form surface with new or used motor oil before setting the form in place. Nail or screw the end pieces securely.

whalers/spreaders

To strengthen and support the outside of the form, make whalers out of two 2x4s fastened together. Secure these whalers to each sidewall at vertical intervals of no more than 3 feet. To attach them, drill holes through the plywood near each vertical 2x4, and thread No. 8 or No. 9 steel tie wires through the holes and around the whalers. Cut some spreaders -- pieces of 1x4 that are exactly as long as the wall will be thick. Have a helper hold a spreader between the vertical 2x4s while you twist the tie wire to secure the whalers in place and tie the whole form together.

level and brace

Shore up the end pieces by nailing 2x4 cross pieces to the ends of the whalers. Check the entire structure for level and plumb. Anchor it with braces nailed to 2x4 stakes every 6 to 8 feet along each side of the form.