The Art of Slipforming

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To set the slipforms, start by snapping a chalk line on the footings for a guide and position the forms along the walls, inside and out; then nail them together end to end. Preferably, the studs on the back of the forms should line up between the inside and outside sets. Now make some temporary spacers from scraps of wood, such as 2 x 2s. These should be cut to fit the width of the wall, and dropped in between the forms to hold the bottoms apart (F). Spacers for de top of the forms are made similarly, but should be nailed onto a thinner piece of wood, like plywood or 1 x 2, and placed across the tops of the forms. The 2 x 2 spacers hold the forms apart, while the longer 1 x 2s are nailed to the tops of the forms to tie the forms together (G). This eliminates the need for a wire tie near the top of the forms. To tie the bottoms together, simply drill holes on both sides of the studs through the back of the forms. Purchase a roil of tie wire at the hardware store, and feed the wire through the forms, wrapping around the studs, and twist the wire ends together outside the forms. Place a nail between the wires, and twist the wires together to pull the forms snug against the wooden spacers (H). There should be a top and bottom spacer, and a wire tie for each stud on the back of the forms.

It is crucial to get the first form setting straight and plumb. Fortunately the slipforms almost level themselves as you tighten the wire ties. A little bump here and there and a few shims are all that is usually needed to straighten and level the forms.

Rebar

Reinforcing bar, or rebar, as it is commonly called, is simply a steel rod embedded in the concrete to tie all the masonry work together. Rebar helps protect your masonry work from cracking or breaking apart if the ground shifts under your house. A small amount of shifting may occur from the weight of the house settling into the ground, but the greatest shifting is caused by earthquakes. Earthquakes put severe strains on a building as the earth rocks back and forth, and the structure aboveground builds inertia in one direction, then gets yanked back in the other direction. Houses built into the earth are affected less because they tend to move with the quakes.

People flee from California each time a major earthquake occurs, but that state is actually one of the safer places to experience a quake. Major quakes near metropolitan areas in California result in surprisingly few fatalities due to the strict construction standards. Quakes of similar magnitude in third-world countries may kill thousands of people because their mud, rock, or masonry houses have no reinforcing bar to hold them together.

People outside of California are overly complacent about construction standards. Although most of the nation may not experience as much seismic activity, all parts of the country are periodically subject to major quakes. It is important to use lots of rebar in your stone walls no matter where you live.

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