How to Build a Retaining Wall the Mortarless Way

©  2008 by Raymond Alexander Kukkee Want to build a retaining wall without hiring a block layer or mason?

Now you can do it yourself. Modern technology and design has made it possible to create almost any structure using a dry, or mortarless system. Specially shaped blocks are easily assembled into terrace walls, retaining walls, and decorative enclosures. With many choices of style and architectural features available, appearance can be highly variable, imitating natural stone, coloured stone, adobe, or even polished rock. The blocks fit together easily and securely.

How Does it Work?

A stone or block "gravity wall" that is "dry" laid without mortar uses it's own weight to resist movement.   It's all in the design.  Some types of stackable blocks have a lip at the rear of the stone that sits behind the lower course. Suitable for lower walls to 4 -5 ft, the weight of the soil behind the wall actually strengthens the structure. Various designs of engineered interlocking blocks are available for higher structures.

The Mortarless Retaining Wall

A mortarless retaining wall prevents soil movement and allows a slope to be terraced and landscaped to maximize use of the area by preventing soil movement and reducing erosion. The advantages of a mortarless wall are many. No concrete footing is required because of the inherent flexibility of a dry wall. To establish a footing, a layer of compacted crushed rock or gravel is placed to minimize settling. A mortarless wall can be easily disassembled and relocated later if desired. Blocks are available in a variety of sizes and widths.  Trim stones, cap stones, pavers and other accessories are offered. Curved walls can easily be constructed. Natural, dry field stone has been used by highly skilled stone masons for the construction of durable walls for centuries. Stackable blocks are the modern version, the engineered answer to retaining walls and structures of all types, and are now considered to be the system of choice by design.  

Build the Wall

Let us examine the process of building a mortarless retaining wall. Initially, a design is required. Design considerations and choices must be made. Will your wall be curved or straight, and what height will it be? Keep in mind, the higher a retaining wall is built, the more critical the structural elements become. Choose two  successive, lower retaining walls to prevent structural problems and simultaneously take advantage of the terraced landscaping potential  offered by that choice. Any retaining wall over 4' high requires structural reinforcement and municipal regulations may even specify additional engineering requirements and fencing for safety. When creating your design, do obtain any necessary building permit and contact your local utilities for location of cable, pipes, or gas lines prior to doing any proposed excavating work.

Tools and supplies you will need 

• Safety glasses and gloves

• Shovel, pick and wheelbarrow (or mini-backhoe service for excavating)

• Tamper or plate packer if available

• Line level and carpenter's level ( use a laser level or transit level if available)

• Carpenter's line

• Wide masonry chisel (or chop saw with Concrete cutting blade)

• Heavy hammer ( 3 lb. Or more)

• Pickets or stakes

• Crushed rock or crushed gravel for the footer,

• Sand for leveling

• Stackable blocks

• Landscape fabric (soil and weed barrier)

• Deadmen galvanized cable anchors for reinforcing ( if wall is high)

• 4" perforated flexible weeping pipe

Let's build it!

1. Design and lay out the wall using pickets, carpenter line, and line level. Measure the physical length, and used the proposed height to calculate the number of blocks required including all of the design elements, including cap stones.

2. Excavate the soft organic soil down to solidified mineral soil below ground level, making the trench wider than the blocks to allow room for a drainage weeping tile on the high side of the wall. The bottom of the trench should be level from one end to the other!   If not, "step" the footing design to match courses, or consider re-designing your project using two or more individual sections of wall instead, keeping the individual sections level.If the wall is split, incorporate that feature to allow an access stairway, or add other features, like a pillars, abutments, or right-angled offset in the wall which can substantially increase the strength of the wall.

3. Add a layer of crushed rock if soil and ground conditions are overly soft! Use a layer of crushed rock or gravel with 6" as a minimum. For soft, bad conditions, use an 10" or 12" layer. Level and compact the footing layer. You may also choose to install a thin layer of leveling sand at this point for ease of leveling the blocks.

4. Lay out the first course of blocks to the line, keeping the course absolutely level. The first course should be not only level, but very securely bedded in the gravel or sand. Use a plate packer if available to flatten, pack, and level the gravel/sand bedding. Tamp the blocks down and remove, or add additional sand to level the successive, lower retaining wall course as necessary. Use a line level from one end to the other to ensure the first course is straight and level.

5. Remember that as with all retaining walls, drainage is always an issue regardless of material or design. Install a length of 4 " weeping pipe level with the bottom of the first course, placing the holes facing down. A strip of ground fabric placed over the gravel will help keep soil and fines from entering the tile. Ensure the ends of the tile are placed to direct any water flow away from the wall.

6. For the second course, alternate the joints, remembering the mason's rule of two over one, and one over two. Start with a half-block as necessary to stagger the joints on every course. Cut the block , scoring with the mason's chisel, or use the chop saw if available. Ensure that all blocks are level and seated properly.  Remember,  the objective is to  build a retaining wall the mortarless way. The blocks must be seated properly dry, without mortar for adjustment. 7. If the wall is high, establish galvanized anchor cables after the second or third course as required for additional structural strength.

8. Install ground fabric behind the wall to prevent infiltration of soil and weeds into the wall.

9. Back fill with gravel immediately behind the wall. In back filling, establish a 12" vertical layer of coarse gravel against the wall to ensure adequate drainage of water. Pack all soil and gravel backfill with a plate packer if possible, to minimize future settling.

10. If the blocks are hollow and require ballast, add ballast stone as specified by the manufacturer.

11. Install the cap stones over the last course and secure as the manufacturer specifies.

12. Complete the landscaping of the terraces as desired, and establish grass by seed and mulch or install sod. Replace lawn and plant accessory bushes and trees as soon as possible to assist in the prevention of erosion.

  Now it's time to build a raised patio to match the retaining wall. Congratulations! You already know how to do it - the mortarless way.

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  Tags:  retaining walls, how to build retaining walls,  yard & garden, mortarless,  DIY,  ground fabric, landscaping