How to Build Straight and Curb & Gutter Concrete Forms Out of Wood

Start all concrete forming with preparation of the site. That typically involves excavation, the depth depending on the type of concrete job, lining with some plastic or moisture barrier and laying a solid compacted gravel base. All concrete needs a secure base. Most jobs, except simple curbings, will also require metal reinforcing and some type of expansion joint. Coat the insides of all wood forms with mineral oil or similar material to prevent concrete from adhering to the wood.

Build straight line forms out of lumber appropriate to the depth of the concrete -- 2-by-4-inch or 2-by-6-inch boards work well for many slabs, sidewalks and similar applications. Set the form boards upright along the slab line and brace in place with 1-by-2 or 2-by-4 wooden stakes set securely on the outside edge of the board; vary the size with the depth of the board. Reinforce with "kicker" stakes set in the ground at about a 45 degree angle and nailed to the upright stakes. Build in expansion joints or plan to cut them in after concrete sets.

Make wooden forms for simple curbs much like straight-line forms for a slab, except with form boards on both sides. Start a plain curb with a trench about 24 inches deep for a 12-inch curb. Build forms with 2-by-12-inch boards on both sides of the curb line. Secure them with 2-by-4 stakes set deeply in the ground, with 2-by-4 kickers outside. Install metal, wood or fiberboard spacers inside the forms every 6 to 8 feet to hold the forms 6 inches apart; secure these with metal clamps or 1-by-2 boards nailed across the tops of the forms.

Use three form lines for combined curbs and gutters. Start with the 24-inch trench. Make the back side of the form with 2-by-8 or 2-by-12 boards set upright and braced with 2-by-4s and kickers. Measure out 18 inches with a tape measure and build inside forms 6 1/2 inches high; this will create a slight slope for the gutter toward the curb. Build an inside curb form with 2-by-6s, set to the same height as the back form. Set wood or steel plates between these boards and clamp tightly together with metal clamps or 1-by-2s nailed across the tops of the forms.

Pour concrete in all finished wood forms, use a rake or board to spread it and use a board to tamp it firmly down into curbing forms. Level the concrete with a board and finish the surface with a trowel once it has begun to set. Finish curbs with a special curbing tool, which makes a rounded edge on the top, when concrete has set enough to remove the front form. Remove the spacers and replace them with fiberboard expansion material.