Building Forms with Clamps and Cross-Ties
Your local concrete equipment retailer can supply you with special equipment for building your own concrete forms: specially designed clamps, which you rent, and cross-ties, which you buy because they remain in the concrete after it sets. Used with plywood and 2x4 whalers, clamps and cross-ties make strong, but easily made, forms. As a further advantage, the ends of the crossties snap off once the form is dismantled, and the conical holes left behind can be plugged. The forms shown at right are for a wall up to 4 feet high. Cross-ties are available for 8-, 10-, and 12-inch-thick walls. Follow the manufacturer’s spacing requirements for the cross-ties, clamps, and whalers.
Tools: Hammer, drill, circular saw, tape measure, level, steel finishing trowel.
Caution! Remove Air Pockets When Pouring Concrete in Forms - Air pockets often develop when pouring wall forms. They usually occur where the concrete adjoins the form surface. If the concrete sets with air pockets still present, the wall not only will be unsightly, but weak. Consolidate the concrete by running a piece of rebar up and down along the length of the form. It also helps to bang the outside surface of the forms with a hammer to settle the concrete against the forms for a smooth, strong finish.
1. Assemble the forms. Fasten a 2x4 kicker plate to the concrete footing using masonry nails. Drill holes for the cross-ties in 3/4-inch plywood, in the pattern recommended by the retailer. For speed, stack the sheets and drill holes through several at once. Insert the ties from the inside of the form and hang the clamps on the ties. Set 2x4 whalers in place and tighten the clamps by tapping them with a hammer. Reinforce corners with 2x4s and plywood.
2. Pour concrete into a wall form. Brush or spray old motor oil on the inside of the forms. Then enlist a helper or two; while one person aims the chute into the form, the other consolidates the concrete. Begin by pouring a few inches of concrete inside the entire form. Then fill 1 1/2 feet at a time to avoid abrupt pressure on the forms. Don’t let concrete harden between passes or the wall won’t seal out water. Strike off the top with a steel finishing trowel.
Building Column and Pad Forms
Column and pad forms are among the simplest concrete projects. They warrant careful planning, however, because these small pieces of concrete provide essential support for decks, wood stairways, and outbuildings. Any outdoor structure that connects to your house should have footings that extend below the frost line. Otherwise, frost heave will stress the junction between the house and the structure and lead to serious damage. Where frost is not a problem, you usually are safe excavating to a depth of 24 inches.
Tools: Posthole digger, round-point shovel, hammer or drill.
Install column forms. A column form simply can be a hole in the ground. Use a clamshell-type posthole digger or rent a power auger if you have a lot of holes to dig. To save on concrete, try to be precise with your digging. Make the bottom of the hole a bit larger in diameter than the top to “key” it into the ground. Shovel in a few inches of gravel before pouring the concrete. Concrete tube forms save on concrete because they are precisely dimensioned. If you want to continue the column footing above grade, brace the form as shown. Otherwise, shovel in a couple of inches of gravel and set the form in the hole.
Make a small concrete pad. To make a pad to support heavy items, such as air-conditioners, transformers, and hot tub spas, dig out all organic material and build a form of 2x4s. Dig postholes that extend below the frost line to keep the pad from rising and falling with temperature changes. Before finishing the pad, check manufacturer’s recommendations regarding the slope required for a particular appliance.
Post-Support Options - Your local building department will have information about the best way to support wooden posts in your area.
■ If you live in a warm area with stable soil, you may be able to skip pouring concrete and set posts atop a precast concrete pier on a bed of tamped gravel.
■ Another effective option is to set a precast pier in a bed of fresh concrete. Twist the pier a little to make sure it bonds well to the concrete.
■ Avoid post rot by installing a raised post anchor. Some of these you set in concrete; others attach to an embedded bolt.