Building the Sun Cottage

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Carefully measure the cubic yardage of concrete that you need to form the 4"-thick slab, and—once again-order a 2,500 PSI mix for all the interior areas. (If you'll be pouring any decks, walkways, or driveways, you'll want to use 3,500 PSI concrete.) Also, don't forget to notify the inspector of your impending pour.

You'll require some help to get the slab down and finished, and I'd suggest that you hire two laborers and a finisher for the day. Concrete finishing is an art ... and though almost anyone can prepare a base for tile, it takes experience (for which the going rate is about $80 per day in my area) to prepare an exposed slab such as the one we use on Sun Cottage. In my opinion, a good finisher will be well worth his or her wages!

Suit yourself up in heavy pants and waterproof boots, and place the concrete as evenly as possible ... using water only when it's necessary to get the mix to flow through the reinforcing mesh. Vibrate the concrete by shaking the reinforcing wire with a hook made of rebar (and by shoveling) until it's a workable mass. When the surface is close to level, you and a helper can screed the slab with a long, straight board worked back and forth in short strokes. At the same time, the other worker can move concrete from the high spots to the low ones with a shovel. (Screeding is very tiring work, so you'll probably want to trade off at frequent intervals.) Once the slab is level, the finisher will smooth the surface with a steel trowel. At this time, iron oxide powder-or some other integral coloring—may be added.

Keep the slab damp and cool for several days after the initial set, either by sprinkling it with a hose or by placing straw or a plastic sheet on top. If the concrete dries too quickly, it will shrink unevenly and likely crack. The most critical period will be the first seven days (when the slab is still considered to be "green"), and you should avoid setting heavy objects on it or exposing it to wear during that time. After a slow cure of 28 days, the concrete will reach its full compressive strength of 2,500 PSI.

With the major concrete work out of the way, we'll move on to constructing and reinforcing the subgrade walls, casting the belt beams, and installing the oak timber kit (or a similar supporting framework) in the next installment of this series. In that November/December article, Sun Cottage will begin to look like a home, so don't miss it!

EDITOR'S NOTE: A catalog of Angus Macdonald's standard designs for low-cost passive solar homes is available for $5.00 from Survival Consultants, Dept. TMEN, 120A West Main Street, Orange, Virginia 22960. Complete plans, specifications, and cost analysis for the Sun Cottage Modular-which is being described in this series of articles-are also available from the firm for $100.

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