Precast Concrete Foundations

Source:www.stonediamondtool.com Date:2013/3/18 Read:1056

While most concrete contractors would prefer to cast concrete foundation walls in place, precast concrete walls have some attributes that make this technique appealing to building owners and builders. For concrete contractors, either erecting or actually casting precast panels could be a lucrative addition to what you can offer your customers.

The most popular precast foundation walls come as nearly finished panels, incorporating insulation and interior studs ready to accept drywall. On site, precast panels go up much more quickly than cast walls, including those constructed with insulating concrete forms (ICF). And since there’s no concrete placed on site, construction can proceed in virtually any weather without concern about freezing or wet conditions. Precast wall erection is also simpler than cast-in-place or ICF construction and can be done by low-skilled workers with only one trained lead. “We feel it is the future of residential foundations,” says Jim Costello of Superior Walls.

Insulated panels come in various configurations, depending on the owner’s requirements. The exterior face of the monolithic panel is 2-inch-thick concrete with integral 6 ¾-inch-deep concrete studs and reinforced bond beams, top and bottom. Standard wall panels have an insulation value of R-5 from 1 inch of rigid insulation attached to the concrete between the studs. Thicker insulation can increase that to R-21. Manufactured in the controlled environment of a precast plant, the panels are typically 8 to 10 feet tall and as long as 20 feet. The panels can incorporate window or door openings. There are no stock panels; walls are cast specifically for each project and each panel is cast with its neighbor to match exactly.

This system results in crack-free and waterproof walls. The panels are made with 5000-psi concrete with low permeability. Since the concrete is cast in a factory setting, all shrinkage has taken place prior to erection of the walls so panels virtually never crack in service. A broom finish is standard for the exterior of the panels, although other finishes are available, including simulated brick or flagstone textures.

No footer

The base for precast foundation panels is crushed, compacted gravel—no footing is poured. After excavation, 4 inches of ½-inch crushed stone is placed and compacted with a drainage system beneath. This base is adequate for most soils and loading conditions. “It can be designed to handle heavier loads if needed,” says Costello.

The panels are shipped from the factory on an A-frame trailer. Panels for a typical home can be shipped using two or three trailers. Erection is handled with a crew of three or four workers, including at least one lead worker who is certified in the process by the manufacturer. Erection requires a 40- to 50-ton truck crane, based on reach, that is located such that most panels can be placed without moving the crane. Panels are lifted with a specialized sling and strongback.