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Calculating Stone Requirements
Calculate the wall width, and from that the cubic volume.

Dry-stack wall width should be 2/3 of the wall height, and the base should be as wide as the wall is tall.

Calculate the tonnage of rock needed by converting the cubic foot volume into tons. Use the standard formula of 15 cubic feet of rock = 1 ton of rock.

Consistency of style from the first rock to the last is essential to the aesthetic appeal of dry-stacked walls, or repairing them.

 
How Much Gravel?
Determine the cubic volume of gravel, with a four inch bed of gravel running the base. 15 cubic feet of gravel = 1 ton of gravel.

 
Digging a Footing
After setting a string line to define the wall, dig a ditch the length of the wall. Shoveling carefully will leave undisturbed soil below. 8 to 12 inches deep it acts as the wall's footing; it will prevent the rocks from sliding forward due to pressure from the earth.

 
Building the Base
Large rocks - flat on both sides - form the base, with a longer and heavy tie-back stone every 3-4 feet extending further behind the wall for added stability.

Place the flat side facing forward, and slanted back about 8 degrees. This 'lean' towards the soil being retained, provides strength. Find appropriately shaped smaller stones to fill the voids between the larger stones.

 
Stable Stones
Every stone set should be secure before another is placed on top of it. Watch point loads and stagger joints, in a running bond pattern if the stones are symmetrical. Each layer is battered - set back 2 inches or so every foot in height.

Constantly compact the backfill dirt as the wall builds. Into all crevices between the excavated hill and the back of the wall, even using a hand sledge for compaction - the best defense against any future washouts. If there are any gaps open, or poor compaction, rainwater will eventually find its way in and jeopardize the structural integrity of the wall.

 
Cap Stones
Flatter and larger stones, chosen partly for visual pleasure, these stones help lock the wall, while keeping rain and bio debris out. A good stone wall cap stones should be walkable.

 
Repairing Walls
Challenges:
1) Missing stones - are there enough?
2) Normally one starts from the corners... starting elsewhere can be problematic.
3) Is the shape of the wall strong? Walls that are straight are stronger than convex curves, as the hydrostatic pressure of the earth behind it finds less resistance. Concave is better, just like the arch, it has inherent strength.
4) Is there an unresolved problem, with water drainage, that will lead to failure soon again?
5) Why has one spot failed and another not?
 
Some Generic Styles
1) Blocky and tightly jointed.
2) Random shapes, with more irregular joints.
3) Thin stones, sometimes with accent stones.
4) Mixed rock, chinked with smaller stones.
 
Plants Add Strength
After you've built your stone retaining wall, you'll want to plant something in the soil being retained, to further anchor it. An excellent low-maintenance choice for sunny areas is "Blue Rug" juniper shrub, a low-growing evergreen.

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This page last modified: March 29 2011