Rob Roy's Earthwood Home

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A concrete floor can be finished in many ways: ours are surfaced with roofing slates, with some floors painted. Throw rugs or mats can soften the floor somewhat. My son Rohan's room has fitted carpet, although the insulation value of the carpet and pad is bound to diminish the heat absorption into the thermal mass a bit. If you've shopped in a modern mall, you know that a concrete floor can be hard on the back and spine. For this reason, our house is designed so that most of the daily activity takes place upstairs, on a spruce plank floor. The two boys have their bedrooms downstairs, and there's a wood store, den, pool table room, and storeroom on that level.

Surface-Bonded Blocks

The walls below grade at Earthwood are built of 16" concrete corner blocks, laid transversely in the wall, much like the log ends of the cordwood masonry. Corner blocks have flat ends; they're nor scalloped like common blocks. The first course of blocks is set in mortar just to establish a good level base course. If care is taken to set these first blocks nice and level, the rest of the block work is a breeze, because no further mortaring is required by the surface-bonded method. The blocks are stacked dry, with just the occasional thin metal shim employed to keep things level or to take a wobble out of a block. The great strength of the wall comes from the application of a 1/8" coating of surface-bonding cement, applied with a flat plastering trowel to each side of the wall. This material, manufactured by several different companies throughout the U.S., gets its strength from the millions of glass fibers that permeate the predominantly Portland cement mixture. The tensile strength—resistance against lateral load, in this case-of a surface-bonded block wall has been found to be about six times stronger than that of a conventionally mortared wall. Mix and apply the cement according to the manufacturer's instructions. It takes a little while to get used to applying the 1/8" layer uniformly, but it is a lot easier—and stronger—than mortaring the blocks in the traditional way. And, the surface-bonded wall makes a great base to which a waterproofing membrane can be applied to the exterior or paint to the finished interior.

With our 36' internal diameter, the effect is that of a truly curved, round white wall. The curve is so gradual that the individual blocks can't be seen. The wall is quick and easy to build, superstrong, light and bright below grade (where light is at a premium), and has phenomenal thermal mass to help maintain steady temperatures: warm in winter, cool in summer.

Will It Last?
Not one of the cordwood walls I've built has ever decayed in any way. They should last a century.

Cordwood Masonry

Above grade, the Earthwood walls are composed of cordwood masonry and plenty of windows for light and solar heat gain. The technique is so elegantly simple that children, grandmothers, and beavers can (and have) all made good use of it. The masonry units are short—typically 12" to 24"—logs that we call "log ends." The log ends at Earthwood are 16" long, most of them cut from old recycled cedar fence rails. Your log ends should be debarked, because insects love that space between the bark and the epidermal layers of the wood.

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