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The Renewable Energy site for Do-It-Yourselfers

When I decided to build my first and last house, I knew I would use alternative building methods. The problem was deciding which alternative to chose. I knew I wanted earth sheltered passive solar, but that still left many options. Choosing to go alternative is easy; finding your way among the myriad methods is not. So, after much study, I chose to use timber frame (post & beam), infill that with cedar stack wall, and slipform stone and concrete foundation walls.

 
Slipformed local stone bedroom wall absorbing solar heat

 

Trying to conserve both money and planetary resources, I cut the timber framing from my property, scrounged cedars where I could, and gathered every stone I could find (and lift) within about five miles of my place.

 

Slipforming is an old building method where wooden forms are set up wall thickness apart. A flat-faced stone is placed against a form, and concrete is poured in behind the stone, forming a wall with embedded stones facing out. Once the concrete has set up, another layer of forms is placed on top, and the process is repeated.

 

Now, with two (or more) layers of forms up and concrete set up, you can remove the bottom forms and leapfrog them up the wall, thus greatly conserving form lumber, as you work your way up and along the wall.

 

Most stones are not very large and heavy. Flat-faced stones do not have to be very thick to cover a fair amount of wall. The heaviest piece of wood in my house is easily heavier than the heaviest stone.

 

In my search for stone, I found several old home sites where the only evidence of a home having ever been there was a stone chimney or pile of stones. This is a tribute to the enduring quality of stone. It won't rot, burn, or get eaten by insects. After you have it mortared in place, it will remain right there, looking exactly like it does, virtually forever. An added benefit is that externally insulated stone is an excellent heat sink, or thermal mass. It soaks up excess solar heat on cold sunny days, and returns it at night.  Conversely, it keeps indoor temperatures cooler during hot days, acting as a thermal flywheel, evening out temperature fluctuations in either direction. And we get all of these benefits from a free resource!

 

We mixed our own concrete, which helped to keep costs below the cost of a block wall, not counting labor. I feel I should mention that the stonework is, in the opinion of many, the most attractive walls they have ever seen.  Another benefit is that unlike the typical stick-framed wall, once you pull the forms and mortar, you're done: no sheet rocking, painting, etc. Plus, there's no maintenance ever. Thick stone walls do not transmit sound very well, either, making for a quiet, attractive, evenly heated interior space.  The walls can be insulated on the outside by applying sheet insulation and stucco. 

Dining area stone wall

Slipforming is an old method, but it is also still used in modern commercial buildings as well. Basically it means using reusable forms, I built mine all 18" high, and either 4', 6' or 8' long, they were 2x4 frames with plywood or boards on one side.  The frames are drilled on the center of the 2x4 every 2', so they can be bolted together.  The process of using them we called "Space, Lace and Brace". 

Space: We started on a poured concrete footer, and placed two 8' forms 12" apart, facing each other, this is for a 12" thick wall. We then took 12" sticks and placed them in a few spots between the two form faces, to keep them 12 " apart.   

Lace: We then wired thru the forms, tightening the wires by twisting nails into the wire, to tension the forms against the sticks. 

Brace: Then we braced the forms by temporarily nailing a 2x4 to the top edge of each form and the other end to a stake in the ground to keep the form plumb.

 We had collected a large pile of stone, any stone with a flat face on at least one side can be used, I just placed one stone at a time against the inside face of the inner form, and then placed concrete behind them, filling in the concrete with what we called "uglies", or stones without a flat face, to use less concrete. Bolt more forms end to end, and go along the wall, building up to the top of the 18" form. We would do about 30-40' a day, mixing concrete in an old gas mixer. After the bottom layer is set up, bolt another layer of forms above them repeat the process, and then when the second layer is set up, you can remove the bottom layer of forms, and use them for the third and successive layers, "leapfrogging" the forms up and along the walls. This process is described in the Nearing's books, which is where I got the idea from, except we put the stone face on the interior, and insulated the exterior for thermal mass. BTW, excellent concrete can be made with less Portland cement by using crushed limestone base mix, it's what the state uses for the base of roadways. 7 parts base mix to one part Portland.

After the walls were built, I troweled on a thin coat of masonry cement to the exterior, called a parge coat, and then painted on a thinned coating of Portland cement to fill pores in the parge coat. After applying waterproofing, I used construction adhesive to adhere two inches of foam board insulation all around the outside walls before backfilling.

 

For further reading: Build Your Own Stone House by Karl and Sue Swenke and
Our Home Made of Stone by Helen Nearing.
Stone House: A guide to self building with slipforms by Tom Stanley

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