Curved Concrete Retaining Wall Forms: ¼-Inch Plywood Works

Homeowner building 23-ft curved (90°) concrete retaining wall (12–24" high). Asks if ¼-inch plywood can form the radius.

Yes, ¼-Inch Plywood Bends

¼" plywood (or Masonite, bender board, composite form liner) bends readily for radii ≥ 3 ft. Wet the plywood first—soak 1–2 hours—for easier bending without cracking.

Formwork System

1. Studs/ribs: ½" plywood or bender board strips (2×4 spacing) cut to curve, screwed to stakes.
2. Face: ¼" plywood screwed to ribs.
3. Spacers: Cut blocks to maintain wall thickness (8–12").
4. Ties: Heavy wire or threaded rod with whalers to resist bowing.
5. Bracing: Diagonal kicks every 4 ft.

Tips

• Oil forms for release.
• Place rebar (vertical #4 @ 16", horizontal #4 @ 12") before pour.
• Concrete: 3,000+ psi, 4–5" slump.
• Strip forms at 24–48 hrs; cure 7 days.

Expert: Mark Harshman | www.prestoexperts.com/expert/markland