A Dry Stone Retaining Wall

Building a dry stone retaining wall is hard work, but it’s also fun. Maybe it’s the low-tech appeal of doing what humans have done for thousands of years. Maybe it’s the satisfaction of turning a pile of rocks into something beautiful and useful that will last for centuries. Maybe it’s the challenge of fitting together a giant, three-dimensional puzzle. Whatever the reasons, many people find working with stone enjoyable and satisfying. You can, of course, turn any pleasant project into drudgery by overdoing it. Two hours of wall-building is enjoyable exercise; six hours is an ordeal. To keep it fun, think of your wall as a summer hobby, to be plugged away at on Sunday afternoons, not a project to be completed in a weekend.

A Dry Stone Retaining Wall

Why Dry?

“Dry” simply means that mortar isn’t used to cement the structure together. Rather, the stones are carefully fit into place and held there by gravity. Mixing up and slopping on mortar is, of course, a nuisance. But that’s not why we leave it out of our wall recipe. A dry stone wall, put together well, will actually outlast a mortared wall for two reasons. It can flex slightly, moving with the ground beneathit instead of cracking like a stiff mortared wall would; and since it doesn’t rely on mortar, it won’t fall apart as mortar wears away, as all mortar eventually does.

Do It Right

Some dry stone retaining walls have stood for hundreds of years, even though they were thrown up carelessly. But building this way is a gamble. A poorly built wall may stand for decades. Then again, it may topple over next spring. Worse, it could come apart as kids play on it, resulting in broken bones. The method we show isn’t the only way to build a dry stone wall; and it certainly isn’t the easiest. But the extra effort pays off with safety and longevity.

Finding Rocks

Gravel pits, quarries, farms and construction sites are good sources of low-cost or no-cost rock. But always ask before you take.

Getting rocks home is the hard part. Building a wall takes a lot of rock (we used 10 tons to build our 35-ft. long, 3-ft. high wall) . So even if you have a fullsize pickup truck, you’ll need to make lots of trips.

For the backyard builder, rocks fall into two categories: angular (like shale, sandstone, marble or slate) and rounded (usually granite). Angular rocks have a definite grain, sort of like wood. So the forces of geology break them into irregular blocks with flat sides and sharp, squarish edges. These flat surfaces make the rocks easier to fit together. They’re also easier to split because they usually break along predictable lines.

Rounded rocks (like the ones we used) are much harder and have a less definite grain. They come in all shapes, but they tend to have humped surfaces. Fitting them together takes a lot more trial and error; you set one in place, find it’s too wobbly and try another.

In most regions, Mother Nature has made choosing a rock-type simple; you just take what you can get. Still, there are a few things to keep in mind while filling your truck or trailer:

  • You’ll need a mix of sizes; everything from baseball-size on up. But don’t play Hercules. If it’s too big, leave it alone.
  • The flatter a rock’s surfaces are, the better. Block-shaped rocks are valuable; round rocks are almost worthless.
  • Long rocks, which are used as “tiestones”, are treasures. The more you have, the stronger your wall.
  • Wedge-shaped rocks are handy for “chinking”.

Finding Rocks

Rock Shopping

If rocks are scarce in your area, or if you have no way to transport them, you can buy a load and have it dumped in your yard. Begin by looking in the Yellow Pages under “Stone” or by calling a landscaping supplier. But don’t just phone in an order. One advantage of buying stone is that it usually gives you a choice of types and colors. So go and browse before you buy.

Prices vary widely, depending on what you get and whom you get it from. A farmer may deliver a load of fieldstone for little more than the cost of transportation. A few tons of richly colored granite from a landscaping supplier may cost you $1,000.

Planning Your Wall

Establish the course of your wall by laying out a garden hose and adjusting it until you establish the path you want the wall to follow. Then cut back the slope and dig the foundation trench.

Here are a few things to keep in mind as you plan your layout:

  • If you have dirt hauled in to create or enlarge a slope, it should be thoroughly soaked a couple of times – by a garden hose or rain – so it settle before you build against it.
  • Big tree roots can slowly tear a wall apart, so you’ll need to cut back any that threaten to reach your wall.

Foundation First

Soil moves as it gets soaked and dries, freezes and thaws. A dry stone wall is flexible and will survive centuries of minor shifting. But big shifts can make it crumble in just a few years.

That’s why a simple foundation and landscape fabric are good ideas. A trench lined with 3/4-in. stone provides drainage and absorbs some movement of the soil below. Landscape fabric, placed against the backside of the wall, keeps soil from working its way into the wall and gradually forcing stones apart.

Smart Stone-Setting

You build a dry stone wall by repeating three steps over and over again: Lay a “course” (a horizontal row of rocks); backfill with subsoil you removed when you cut back the slope; and “tamp” or pack down the backfill. Then on to the next course. Pretty simple, but not necessarily easy. Here are some time- and labor-saving tips:

  • Building with stone is like putting together a jigsaw puzzle. So begin by spreading out the rocks just as you would the pieces of a puzzle.
  • Put your best, wide, flat stones aside to be used as capstones.
  • Use your biggest stones for the first course. That way you won’t have to heave them up into place later.
  • If, after the first course, you have a few biggies to raise onto the wall, use a wood plank to roll them up into place.
  • Fitting stones together is mostly trial and error. Cut down on both by mentally measuring the shape and size of the stone you need first Then go hunt for the perfect fit. You may even want to use a tape measure.
  • Stone cutting is no fun. And doing it well is difficult. So we recommend you don’t. But if you must, you can knock off troublesome crags or knobs with a hammer and cold chisel. If you do, wear eye protection and keep others out of the flying-stone zone!

Tip: Carefully choose rocks for the face of the wall. If you have different colors, mix them into a patchwork. For a neat, geometric look, lay stones with their flat sides facing out; for a rustic look, leave rounded, irregular sides exposed.

Ten Commandments of Stonebuilding

  1. Make “one over two, two over one” your wall-building motto. Lay the stones of one course over the vertical gaps between stones of the previous course; just like a bricklayer lays bricks. If you don’t do this, you get “vertical run” and a weaker wall .
  2. Use tiestones, long rocks laid perpendicular to the face of the wall. You’ll need one tiestone at least every 4 ft. on each course. But you can’t have too many; the more tiestones, the stronger the wall.
  3. All rocks on the face of the wall must slant down toward the inside of the wall. Those that don’t will eventually fall out.
  4. Keep it roughly coursed. If you’re working with very irregular stone, you’re likely to build jagged, uneven courses. This makes the next course harder to fit together. Soon you have no courses at all and lots of vertical run. Try instead for roughly even courses, by avoiding peaks and filling in valleys with smaller stones.
  5. Lay rocks flat, not on edge.
  6. Use chinking, small stone wedges driven between larger rocks, to tighten up loose-fitting rocks and fill gaps in the wall’s face.
  7. Make it as thick as it is high. If your wall will rise 3 ft. above the ground at its base, the course under the capstones should be 3 ft. thick.
  8. Don’t build it more than 4 ft. high. The higher the wall, the more potential for injury should it collapse.
  9. Don’t make the face of the wall perfectly vertical. To hold back all that earth, it must lean into the slope. A minimum of 2 in. of backward tilt for each foot of height is a good rule of thumb.
  10. Mortar if you must. You should have large, tight-fitting capstones that will stay solidly in place by themselves. If not, cement them with a mortar mix like Quikrete or Sakrete.

Ten Commandments of Stonebuilding

A Freestanding Wall

A freestanding dry stone wall is similar to a retaining wall, but with a few variations. You have to be more fussy about the fit of the stones. A retaining wall leans against a solid mound of earth. A freestanding wall leans in on itself, so the two faces must slant into each other and lock together. The key to a strong freestanding wall is “V-slant.” Each course must be highest at the faces, with a gradual depression in the middle. With each stone tilting down toward the middle, gravity holds each in place and the entire wall together.

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