Form Footing - Bracing Upper Form-A-Drain
To stop the Form-A-Drain bowing it needs to be strengthened with lumber.
Bracing outer upper Form-a-drain
Horizontal lumber bracing
The outer upper Form-a-drain is susceptible to bending and warping and generally flapping around. It needs to be stiffened up so that it stays straight. This is done by attaching 2x6 lumber round the outside. The actual dimension of lumber I use from my sawmill after edge trimming on a table saw is 1.5" x 5". The 2x6s are attached using 2x4 on the edge to form an L. The 2x4 has hole pairs every 6".
You will need to make them in sections as the 2x6 lumber is not anything like as long as a length of Form-a-drain. Use the longest lengths of 2x6 as you can easily obtain. Choose only nice straight lumber. The 2x6 is attached to the lower edge of the 2x4. The top holes in the 2x4 are for screwing into the Form-a-drain. The 2x4 piece stops short of the end of the 2x6 in order to provide clearace for the Form-a-drain corner joins.
The L-shaped lumber assembly should be installed 1.75" below the top of the Form-a-drain so it is clear of the top reference edge (even if an extra buttressing piece of 2-by is added on top). I use a 1.75" spacer wooden block to set the height.
Use 2.5" wood screws about every 6" to screw from the 2x4s into the Form-A-Drain. Be careful not over tighten the screws as this would strip the plastic of the Form-a-drain..
At the corners use 45 degree points as it provides clearance from the excavation earth.
Connect pieces of long 2x6 using joiner pieces of about 2 foot length (I use 2'2" as I can get two pieces from the 4'6" lumber that conveniently comes from my sawmill).
Also use overlapping pieces of 2x6 at the corners. The same design of joiners can be used on both outside and inside corners.
Ensure the Form-a-drain is exactly straight as you attach the joining pieces. This can be done by looking along the length to ensure straightness and more importantly using plumb-bobs from the batterboard strings.
Bracing outer Form-A-Drain
To give something solid to attach bracing, it is good to use the batterboard steel stakes. Lumber pieces should be attached to the stakes near the ground so any force does not bend the stakes (which would upset the batterboard location). Use screws through the stake holes and also put lumber on both sides of the stakes and screw together.
You can creatively make use of any nearby structures such as a work shed.
Where there are not suitable batterboard stakes or structures then you will need to add extra stakes.
Where there are nearby columns you can brace to them. Attach the bracing to the bottom-most column stem square as this is the most firmly sited.