Slab Foundation Construction

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    • 1). Level the site and clear it of tree roots, large rocks and other debris. Lay out the slab perimeter with wood stakes and builder's twine. Measure it diagonally to make sure it is square; if the two measurements are the same, the site is square. Make sure it has the proper street setback and is square with the lot lines.

    • 2). Install all rough plumbing elements. Put in drain pipes for sinks and toilets, water supply lines for all faucets, washer connections or other water needs. Put in gas lines if those need to be installed before the slab is finished. Make sure drain and other connections extend well above the finished slab height. Cover openings so no concrete or other material gets inside.

    • 3). Dig a footing trench around the perimeter. The depth will vary; in areas where ground freezes, footings must be below the freeze line; in other areas footings may need to be only a foot or so deep. Check local building codes for specifics. Make footings about 16 inches wide. Put down a layer of compacted gravel. Insert upright reinforcing bars about every 4 feet, extending up above ground level and lay some reinforcing bars lengthwise in the trench. Pour the trench with concrete up to ground level.

    • 4). Build a stem wall form around the perimeter, with 2 by 12-inch boards or plywood panels formed over 2 by 4-inch frames. Secure the form with stakes driven in the ground and braced diagonally with other stakes. Make the stem wall to within 4 inches of the finished slab height. Insert vertical and horizontal reinforcing bar. Make the vertical bar extend a foot or so above the stem wall top. Pour concrete to the top of the form.

    • 5). Excavate the interior of the slab perimeter at least 8 inches deep. Put down 4 inches of compacted gravel, to about the level of the stem wall. Build another form on the outside of the stem wall to 4 inches above it; use 2 by 12-inch boards or plywood forms, staked in place. Bend the vertical rebar in the stem wall down into the slab area. Lay rebar across the slab area in a grid pattern, fastening it with wire at the intersecting points. Slope the gravel at the perimeter down a couple of inches at the stem wall, making a small trench around the edge.

    • 6). Pour concrete over the slab area. Level it with a long 2 by 4 or metal screed, dragged across the slab at the height of the slab forms. Put one person on each end of the board outside the slab and work the screed across the concrete to even it. Finish the surface with a trowel when the concrete has started to set, working on a board across the forms and moving down the surface of the slab.

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