How to Build a Boulder Retaining Wall

Cost

$ $

Skill Level

Start to Finish

2 Days

Tools

shovel
plate tamper
48" level or line level
rake
utility knife

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Materials

natural boulders (ideally rectangular; one pallet will build a 3’x10' wall)
coarse gravel , size 5-7 stone (approx. 1 cubic yard per 5’ wall)
roll of soil-blocking fabric, at least 4’ wide

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Step 1

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Excavate Location of Retaining Wall

Lay out the location of the retaining wall, and excavate the bank approximately 2’ deeper than the proposed front of the wall.

Step 2

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Dig Footing and Level

Dig footing approximately 2’ wide and a depth of a least 8”. Ensure the base of your footing is level using a line level or long bar level.

Step 3

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Compact Loose Soil

Be mindful not to loosen dirt at the bottom of the footing. Use a plate tamper or shovel to compact soil if loose.

Pro Tip

If the elevation of the footing drops more than approximately 6”, step the footing down by making a shelf where the footing will be lower. This keeps the footing level while still following the grade.

Step 4

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Fill Footing

Fill the entire footing with coarse gravel, spread evenly and compact with a plate tamper or shovel.

Step 5

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Level Footing

Level the top of the gravel footing using a long level or line level. Smooth the surface with a garden rake and plate tamper.

Pro Tip

Use a rotating laser and receiver for long distances to improve accuracy.

Step 6

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Place First Row of Boulders

Place the first row of boulders, positioning the desired boulders outward.

Pro Tip

Position boulders flattest side on top. This will make the next layer easier to fit.

Step 7

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Place Second Boulder Layer

Continue with the second layer, ensuring the wall is slightly moving back towards the bank. Ideally, the wall should have a backward angle at approximately 1/2" to 1'.

Pro Tip

Rotating longer stones to periodically face into the bank will give you more options for fit and will provide more stability to the wall once backfilled.

Step 8

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Place Landscape

Place soil-blocking fabric on the back of the wall and on the dirt bank. Ensure there is enough fabric laying on the top of the wall to cover the dirt.

Step 9

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Backfill Soil to Wall

Fill the space behind the wall and the bank with coarse stone, stopping about 8” below the top of the wall. Cover soil with remaining fabric and backfill soil to the wall.