Form Materials for Curved Footing

[Toad]

I have to pour a 8" deep x 18" wide footing for a 100' long retaining wall that will have a 90 degree curve. The will be an adjacent slab poured for a patio, so there was a lot of excavation. After the base material is compacted, all 8" of the form will be above ground.

My question is what type of board(s) should I use for the curved and straight section of the formwork. 1x8 boards don't seem flexible enough to bend correctly, and might be too thin for proper support anyway, right? On the staight sections I could use a 2x8 (I know the nominal width is less, but figured it wouldn't be a big deal), and how do I make that transition?

Oddly enough, all the do it yourself books don't address this type of problem for concrete pours thicker than 4 inches.

Any help greatly appreciated. Are there other, easier materials out there that would be good for what I am trying to do?

[doyle]

How tight of a radius are you trying to make for your 90 degree turn?

[RobBase]

Toad, why is your footing going to be exposed/above grade? Do you live in the south where there is no need to have the footing resting below the frost line?

Regardless, if you want to make it a nice, round, exposed footing, go buy a sheet or two of 1/4" masonite. Rip it down to 18" pieces x 8'. Put a stake in for your radius point, then hook your measuring tape on it and layout/stake some metal form pins every 6-8" along the inside circumference of your footing. Lay 2 pieces back to back (effectively 1/2" thick) of the masonite on the ground against the pins and start bending it around by putting pins on the outside circumference of the footing. Continue all the way to the point where the footing straightens out and cut the masonite off at the point where it will tie into your straight forms.

Leave the inside pins where they are until you fill the forms up with concrete. While it's still soft pull the inside pins out and tap your forms to fill the voids.

[Toad]

Sorry, guys. I did a poor job of explaining. The top of the footing will be below the final grade of the adjacent patio----it's just going to be exposed during the form and pour above the existing grade after excavation. I am doing the retaining wall before the patio slab. This is in my back yard, which used to be sloped. I cut it back, removing about 180 yds of adobe.

Doyle, the radius is not a sharp one---about 8 feet. I was just flummoxed about finding the right form dimension for the 8" thickness I wanted for the footing.

The masonite suggestion sounds like a good one. I wonder if I ought to just use that material for the straight section as well.

Thanks for the help.

[RobBase]

The masonite suggestion sounds like a good one. I wonder if I ought to just use that material for the straight section as well.



No. Use some 2x8's for the straight forms. The masonite is very flimsy and only holds up to concrete if you use many, many form pins. It's not worth the extra effort.