How to Build a Mortar-Free Wall with Interlocking Retaining Wall Blocks

Use interlocking retaining wall blocks to build a mortar-free wall. Follow our step-by-step instructions to build one in your yard.

Project Overview
  • Total Time: 15 hours
  • Skill Level: Intermediate

Interlocking retaining wall blocks are good for building a solid wall without mortar. Some blocks are made with flanges that slip over the rear edge of the preceding course; others rely on a system of pins. You don't have to practice throwing mortar or setting blocks with either type, but you'll get an attractive addition to your landscape. The flanges slope the wall back into the slope for additional strength.

An interlocking retaining wall doesn't require a footing, but some styles need you to set the first course in a trench to hold the bottom of the wall in place. Cut the slope back 12 to 15 inches from the rear of the trench to leave room for gravel backfill and a drainpipe—a must for retaining walls. Save the topsoil and use any extra as fill elsewhere in your landscape.

To lay a 3x16-foot wall, expect to spend 10 to 20 hours. You'll need to feel comfortable digging, designing a layout, leveling, and laying brick. Before you begin, call your local hotline to mark any underground utilities.

What You'll Need

Equipment / Tools

  • Measuring tape
  • Shovel
  • Tamper
  • Level
  • Circular saw
  • Small sledgehammer
  • Rubber mallet
  • Torpedo level
  • Brick set
  • Caulk gun


  • Landscape fabric
  • Gravel
  • Drainpipe
  • Landscape blocks
  • Construction adhesive


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    Lay Out Wall

    Lay out the wall and remove the soil from the slope. Following the manufacturer's recommendations, dig and level a trench for the first course. Stake a mason's line to help align the blocks.

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    Spread Landscape Fabric

    Starting a foot beyond the top edge of the slope, spread landscape fabric down and over the trench. Put stones on the top to hold the fabric in place. Overlap the fabric edges by 6 inches. Tamp 3 to 4 inches of gravel into the trench and back to the bottom of the excavation.

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    Lay the First Course

    Using the line or the edge of the trench to guide you, lay the first course in the trench. The first course blocks are set backward for many styles. Set each interlocking retaining wall block with a rubber mallet. Make sure each block is level front to back and with the adjoining blocks. Use a 4-foot level to check—shorter levels are not long enough to ensure accuracy. If you need less than an entire block at the end of the wall, lay smaller blocks or trim blocks to fit.

    Precast block is trimmed the same way other masonry materials are trimmed. If you're using solid block, score the line you want to cut with a brick set and a small sledgehammer. Repeated blows will split the block. Hollow-core blocks don't break cleanly. Buy half and smaller blocks to fit where you need them, or cut them with a masonry blade.

  4. Set Remaining Courses

    Set the remaining courses with the flanges tight against the back of the preceding course. Start every other course with a half or partial interlocking retaining wall block, so the joints are offset by at least 3 inches or the amount specified by the manufacturer's instructions. As you work, check the blocks for level. Shim the low end of a block with a small piece of cedar shingle.

    Some blocks have pin-lock systems (see illustration, above). One of the most common employs vertical and horizontal pins. Blocks fit over the vertical pins as you lay them. After laying each course, horizontal pins lock the blocks laterally.

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    Set Up Drainpipe

    After the third course of interlocking retaining wall block, backfill the area between the wall and the slope with gravel, just about even with the second course. Lay in a perforated plastic drainpipe on the gravel (holes down). Let the pipe daylight beyond the edge of the wall, or run it into a French drain.

    If your wall is designed with corners, the corner blocks must overlap at the joints to tie the two legs together. Cut half blocks and alternate them with whole blocks as shown, following the manufacturer's instructions. Chisel off the lip of the block if it gets in the way. As you place the block, strengthen the bond with a bead of construction adhesive.

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    Backfill Wall

    As you build the wall, backfill gravel behind it at least every other course, covering the pipe and bringing the gravel level up just below the top of the last course you laid.

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    Tuck Fabric

    Using the same techniques and starting every other row with a partial block, continue building the wall and backfilling it with gravel. When you're one or two courses below finished height, fold the landscape fabric over the gravel and tuck it behind the block.

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    Tamp Soil

    Shovel about 2 inches of the topsoil you removed (not the subsoil at the base of the slope) on top of the landscape fabric. Tamp the soil lightly with a garden rake and replace the sod.

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    Apply Adhesive

    The capstones made for block of this or a similar shape cover the V-shaped gaps between blocks in the lower courses. Prepare the next-to-last course by applying a bead of construction adhesive on the surface of each block.

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    Place Capstones

    Following the manufacturer's instructions place the course of capstones on the wall.

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    Finish Base

    If you're not building a patio or other structure below the wall, spread and tamp the topsoil you removed from the excavation. Fill in around the base of the wall and level the soil as far forward from the base as the landscape allows. Tamp the soil and replace the sod. Water the sod frequently until it is well established.

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