The Art of Slipforming

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Stone houses have both enduring and endearing qualities about them. Enter one and an immediate and palpable aura of timelessness becomes apparent, and makes all other forms of consturction seem fragile in comparison Building with materials as old as nature also makes a home seem as if it were part of the story of the land. A monument to your family.

The method of stone masonry we use is called slipforming. Short fortes, up to two feet tall, are placed on both sides of the wall to serve as a guide for the stonework. You fill the forms with stone and concrete, then "slip" the forms up for the next level. Slipforming makes stonework easy, even for the novice.

Slipforming is an old-fashioned style of masonry, resulting in a random or "rubblestone" appearance, without the uniform joints or sharp, clean lines of most modern masonry. In fact, slipforming is comparatively messy, and you will often find cement drips permanently adhered to the face of the rocks when you remove the forms. Rut these stains also contribute to the "patina" of the stonework, giving it an antiqued appearance. We rarely remove the drips, even when we can.

Overview

Slipforming combines stone masonry and concrete work to form a wall that shares the attributes of both. The walls have the beauty and strength of stone with the reinforcement of concrete and steel. The final product is long-lasting, low maintenance, and virtually weather- and fireproof.

The literature available when we started building showed walls that were stone outside and concrete inside (the letters A through H mentioned in this article refer to illustrations on pages 62 and 63). These had frame walls built against the concrete for holding the insulation and attaching the plasterboard (A). This combination always seemed inefficient to us, partly because of the duplication of the structural wall, but also because the studs are conductive gaps in the insulation. We have avoided the need for the interior studs in some projects by using adhesives to glue rigid insulation and plasterboard directly to the concrete (B). (The wiring and plumbing is routered into the insulation.)

We also like our homes to feel as natural on the inside as on the outside, so we always build some walls with stone inside and out, with rigid insulation in the core. To do this we form both walls at the same time and push short pieces of rebar horizontally through the insulation to tie the walls together (C). In our home, some of the stone walls are completely inside the house, positioned to support the log upper story while being protected from the weather by the greenhouse in front. These walls have no insulation in them, and are simply formed with stone on both sides and concrete in the core (D). (Wiring and plumbing can be placed in this type of wall, but I do not recommend it for the beginner.)

The width of each wall in the drawings is determined by the amount of room needed for the stone and concrete and by the size of the dimensional lumber used for framing in the doors and windows. A 2 x 10, for instance is really 9 1/4 inches wide, so we make the walls that width and screw the slipforms directly onto the faces of the window or door frames.