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Every three to four courses, 1/2" rebar is driven vertically through the wall, about 4' apart. Some experienced builders also recommend laying a piece of 1/2" rebar horizontally down the middle of every third course and wiring it to the vertical rebar to further strengthen the wall.

If you are using slip forms, any convenient depth is fine. These days most builders are using 8"-deep forms. (If the wall is 12" wide and the form is only 8" deep, there is no danger that a form full of slurry will tip over.) With forms, a thicker slurry is better. Andy drained his papererete on a piece of shade cloth for several minutes before pouring it into his forms, thereby reducing shrinkage and cutting down on water penetration into the already poured wall below the form. He was able to remove his forms 30 minutes after he had filled them with slurry.

Slip form walls are reinforced with rebar just like block walls.

If you plan to build with slip forms, be forewarned: Though self-supporting even when wet, newly poured walls will need to be securely braced until they dry to ensure that they remain perfectly vertical and to prevent accidents, should, say, somebody bump into one of them. After removing the forms, bullders often prop wet walls with vertical 2 x 4s, braced with a second set of 2 x 4s placed at a 45° angle.

Once dry, the walls become exceptionally strong. As Andy says, "You could crash a car into my house and nothing would happen - except to the car."

ROOFS

We have never heard of a concrete bond beam being used on a papercrete building. Most builders use a wooden bond beam - 2" thick lumber, the width of the wall, pinned to the wall with rebar. The rebar is bent over at the top so the bond beam won't lift off the wall in a high wind.

Virginia used a conventional truss roof nailed to her bond beam. Andy made a papercrete roof without a bond beam. Spacing vigas every 30 inches, he drilled holes through them and pinned them directly to the wall with rebar. Then he laid 2" x 4" woven hog wire over the vigas, stretching it as tightly as possible to reduce sagging. Next, he put on two layers of 1" chicken wire, staggering the layers so that the maximum space between wires was a half inch. Over this, he poured a 1" layer of papercrete and allowed it to dry. (He didn't apply the entire thickness of papercrete all at once, because he didn't want it running through his wires.) He used two bags of cement per batch for extra strength, and he didn't use any sand to minimize the weight.

Not wanting to lift all that heavy slurry up to his roof, he bought a 2" gear pump, with which he pumped up a total of 12 yards of slurry (24 mixerloads). It worked, though the pump was starting to show signs of wear by the time he was through. After the first 1" layer was dry, he pumped on an additional 4" layer, allowed it to dry, then pumped on a final 2" layer.

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