DO-IT-YOURSELF : Stone Wall Holds Up Under Gravity

A dry, unmortared stone wall is held together by friction and gravity. It is attractive and a good space divider, although it can’t be built high enough to give privacy.

It usually consists of two wythes (parallel tiers) of larger stones, with smaller stones used as filler. To tie the structure together, bonding stones--long, flat stones spanning the wall’s full width--are set at regular intervals in the wall.

For maximum strength, build the wall on a five-inch bed of sand in a six-inch-deep trench. Unless you’re an experienced stonemason, it’s best to limit the height to three feet. Make the width of the base two-thirds the wall’s height. For example, a three-foot-high wall would need a two-foot-wide base.

To keep a dry stone wall from collapsing, the weight of each stone must press straight down on the stones below it. Position each stone so that it rests securely on a firm, flat bed and overlaps two or more stones in the underlying course. For greater stability, the ends and faces of the wall are battered (sloped toward the center).

Obtaining Stones

In rocky areas, you may be able to gather all the stones you need on your own property or in nearby fields. Otherwise, buy them from a local stone yard or quarry. Try to select larger stones that weigh less than 30 pounds. To top off the wall, you will need very broad, flat capstones for the entire length.

Trimming Stones

If some stones need trimming to fit better, mark cutting lines with a grease pencil, following the stone’s grain. Place the stone on another stone or the earth and use a chisel and sledgehammer to score along the line. Place the chisel on the scored line and strike hard with hammer. Wear leather gloves and safety goggles. Try to observe a stonemason before attempting to do it yourself.

Setting the First Course

* Outline the wall with tall stakes and tie string on them at the height of the first course of stones. Set bonding stones at both ends of the trench, and every four feet between, on the sand bed. Using the heaviest stones, lay the first course.

* Make the first course of two wythes as level as possible. Place each stone with its flattest side up, its next-best side facing out. Seat each stone securely in the sand bed. Fill the center between the wythes with small stones.

* To check the wall’s slope, or batter, make a batter gauge by nailing three one-by-two boards to form a long narrow right triangle. The gauge’s height should equal the wall’s height; its base the required batter of one inch per foot of height. If the wall will be three feet tall, for example, make the gauge three feet high with a base three inches wide. To use the gauge, invert it so that it points downward and use a level to keep it straight.

Second Course and Finish

Raise the string line to the height of the second course. Using the string and the batter gauge as guides, lay the second course so that it’s set in slightly from the first. Slope large stones toward the center. Stagger vertical joints and place bonding stones every four feet.

* Build up the wall course by course, choosing stones that fit snugly and make a fairly even bed for the next course. Use small stones as needed to shim up larger ones and to fill chinks.

* Save the broadest, flattest stones for capstones--the wall’s top course. Most capstones should span the width of the wall. You may want to set the top course in mortar.