Capping an old foundation with new concrete is relatively rare but is done when the existing foundation is in good condition and needs to be raised because the house’s framing is too close to the ground, allowing surface water to rot sills and siding.
To raise wood members sufficiently, the new cap must be 8 in. above grade. At the very least, that means shoring up the structure, removing the existing mudsill, shortening the pony-wall studs, drilling the old foundation, epoxying in rebar pins to tie the new concrete to the old, and pouring new concrete atop or around some part of the existing foundation. That’s a lot of work. So if the existing foundation is crumbling or lacks steel reinforcement, you should replace it altogether.
On the other hand, if the house lacks pony walls and the joists rest directly on the foundation, you have basically two options: (1) grade the soil away from the house to gain the necessary height, which may not be possible if the foundation is shallow, or (2) jack up the house at least 8 in., which means hiring a house mover. Here again, replacing the foundation is usually more cost effective.
Otherwise, cut the tops of the stakes off and leave the rest embedded in the new concrete.
Hammer the outside of the form boards and then use a concrete vibrator, to drive out the air pockets. For this, insert the hose-like vibrator into the forms. As the concrete approaches the tops of forms, signal the pump to shut off so that the concrete doesn’t spill over the sides. When the forms are full and vibrated, use a trowel to flatten the top of the wall and sponge off any globs on the stakes and forms. Allow the concrete to cure 3 days at a minimum and 7 days for the optimum, before removing the forms and shoring, replacing the siding, and tightening down the washered anchor bolts. For further protection against moisture, apply below-grade waterproofing to the outside wall and footing before backfilling.
Concrete is a mixture of portland cement, water, and aggregate (sand and gravel). When water is added to cement, a chemical reaction, called hydration, takes place, and the mixture hardens around the aggregate, binding it fast. Water makes concrete workable, and cement makes it strong. The lower the water to cement ratio (w/c), the stronger the concrete.
Pouring (or placing) a concrete slab is pretty much the same procedure, whether for patios, driveways, basements, or garage floors. Most
