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How To Build Retaining Walls With

Natural Stone

Photo: example of the dry-stack method.

David Beaulieu

This tutorial is on building retaining walls out of natural stone, 3 in height or less, using a dry-

walling or "dry-stack" approach. Other materials for building retaining walls include timbers or

salvaged railroad ties, concrete and landscaping block (such as you see at Home Depot andLowes). The dry-stack method is not appropriate for terraces greater than 3 feet in height.

Difficulty: Average

Time Required: 2 days for a 10'-long structure.

Here's How:

1. Check local codes before you begin digging (you may need a permit), although often youwont be bothered if you keep the structure 3 high or less. If your slope is too large for a

3-high structure, you could terrace the slope by building retaining walls in 2 or more

places, rather than trying to do the whole job with just one structure. Building terraces

greater than 3 in height is trickier. The mortar-less method discussed in this tutorial is notintended for such projects.

2. The great virtue of stone retaining walls that are mortar-less is that your drainage system

comes built-in: water will usually seep through the cracks between the stones. Whendamage from water pressure does occur, it can be repaired easily enough. Another

advantage in building terraces of this sort is that you do not have to sink a footing

beneath the frost line, as you do when using concrete or stone and mortar.

3. Select stones that have at least two sides that are flat (what will become the top and the

bottom once in place in the structure). The heavier the stones, the more stability youll

have - but also the harder the work (but it will be worth it).4. Plot out where the retaining wall will sit at the bottom of the slope, using stakes and string

for a straight terrace, a garden hose for a curved one. The advantage of a straight terrace is

that you can attach a line level to the string to make sure the courses of your retaining wall

are level.

5. Dig a trench about 8-10 deep, so that the first course of stone is fully or mostlysubmerged. This will help your retaining wall withstand the pressure exerted on it by the

slope it is holding back.6. To calculate the necessary width of the trench, just remember the base of the structure

should be half the walls height. Angle the trench so that it inclines back slightly into the

slope (2 for every 1 of terrace height) this will provide greater stability.

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7. When youve almost penetrated down to the required depth, use a skimming motion to

remove the remaining soil, so that you dont end up with a base of loose soil. Keeping the

base as solid as possible will reduce the chances of shifting as the retaining wall settles.8. Terraces of natural stone are laid in courses, i.e., a horizontal row at a time. The first

course of stones will consist of your largest, widest, longest, flattest stones (but save some

for the final course, the capstones). They have to be the most stable stones. Take the timeto fit them as closely together as possible. Building terraces with natural stone is like fitting

the pieces of a puzzle together - only its a puzzle that can turn out many different ways.

9. In terms of the height of the first course of stones and the following courses, you have twochoices. If youre aiming for a look of uniform rows, choose stones of the same height

when laying a particular course. The other option is a more random look, in which you play

each course by ear, using filler stones wherever necessary to make up for a difference in

heights. Sometimes you are forced into the latter option, because the stones you have towork with simply arent uniform enough.

10. Check to ensure that the stones run level left to right. But because youve built a slight

backwards slope into the trenchs base, your stones will slope down slightly front to back.

After completing this first course (the foundation, if you will) backfill with some of yourexcavated soil and any stones too small to use for building the retaining wall, and tamp it

down.11. In laying the next course of stones and those that follow, avoid lining up the joints over the

joints of the course underneath. Again, backfill and tamp down after completing the course.

Also tuck soil in between any gaps in the terrace, to serve as chinking. When yourefinished building your retaining wall, you can root plants into this chinking and bring life to

the structure. Cascading plants, such as thyme and the annual, lobelia are very attractive in

stone retaining walls.

12. As you place each stone, check that theres as little wobble as possible. To counteract anywobbling, you may have to use small, flat rocks as shims. Use a mason's hammer to

knick off stone fragments so as to achieve a better fit where possible.

13. Continue in the same manner with the third course and succeeding courses. By the timeyour terrace is half its planned height, you should start incorporating what are known as

deadmen. In the case of stone retaining walls, the term refers to long stones laid

perpendicularly across the wall, rather than parallel to all the other stones. The idea behinddeadmen stones is to tie the structure into the slope in back of it.

14. A hole is first dug into the slope to incorporate a deadman. Then one end of the deadman is

set on the terrace (as part of whatever course you happen to be laying), and the other end

placed into the hole youve just created in the slope. The longer the stones you can find toserve as your deadmen, the better. The Colorado State Extension states that A good rule of

thumb is to provide at least one deadman per 16 square feet of exposed wall face.

15. When youve almost reached the desired height for your terrace, its time to place thecapstones on top. Capstones are similar to the stones used in your first course, in the

sense that they should be flat and have significant mass. They serve both to help hold the

stones under them in place and to provide a finished look to the structure (thus theimportance of their being flat).

Tips:

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1. 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.

What You Need

line level and string / garden hose

shovel

mason's hammer

stakes

carpenter's level

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