How to build a Retaining Wall with Blocks

Updated: Feb 8

Want to learn how to build a retaining wall? Learn the installation process required to build a beautiful Retaining Wall that will last for years to come. We’ll cover everything you need, retaining wall blocks, including tools, layout, equipment, base preparation, gravel selection, stacking, backfilling behind the wall, and installing the capstones (marking & cutting).

Before we begin, in most areas retaining walls 4ft tall and over require a permit or possibly an engineered drawing to legally construct the retaining wall. In some areas, the height restriction is 6ft tall and over requires an engineer to design a retaining wall.


So be sure to check your local codes to see what is required of you to proceed. Once you have engineered drawings approved by the city. You can begin construction, following the retaining wall blueprints exactly.


Retaining Wall Blocks

There are a few different styles of retaining wall blocks that should be considered for your project. Some are interlocking while others require the use of concrete adhesives and locking pins to create the structural bond.

Hollow Block style and Solid Block style both have interlocking features and/or require concrete adhesive.


Hollow Blocks are just how they sound, with a hollow center and durable perimeter. These blocks are typically taller than their solid block counterpart.


The average Hollow Block is 8 inches compared to 6 inches with solid blocks. The hollow center makes it a bit trickier to persuade with your dead blow hammer (small surface area to hit)


Solid Blocks are completely solid and are about the same weight if not more than a hollow block. They are easier to use a dead blow hammer to level your block during base course install.


Fascia wall systems are composed of a core unit(s) that has features allowing a face unit to attach to it, in some instances concrete adhesive can be used for a more permanent application.


Some popular providers of retaining wall products are Unilock, Techo Bloc, Belgard, Pavestone


Footer

Retaining wall footers should be composed of at least

  • 6 inches thick of gravel

  • 6 inches beyond the face(front)of the block

  • 18 inches beyond the back of the block- at least, sometimes farther

  • Average Footer is 3 ft. wide or more by 10 inches deep

  • Footer drain with cloth covering or another filtering material

Anything less than mentioned above will decrease the integrity of your retaining wall project, likely leading to failure.


Try not to disturb more soil than needed during excavation, if you do be sure to compact adequately.


Layout

Before beginning construction on your retaining wall, you should layout the planned excavation zone, the footprint of the footer, mark utilities, inspect grades and elevations.

  • Plan to excavate at least 6 inches beyond planned retaining wall footer

  • Mark utilities before excavation

  • Plan material staging

  • Where water will be directed from the footer drain

  • Setup grades stakes

  • Mark excavation zones with spray paint or stakes


Tools & Equipment

When you plan to build a retaining wall you are going to want some tools and equipment to help you get the job done. Maybe some helpers too, many hands make for light work. Otherwise, you will likely need most if not all of the following:

  • Deadblow Hammer

  • Shovels-(flat and pointed)

  • String line & stakes

  • Levels:

  • Line level

  • torpedo(1ft or less)

  • 3ft or 4ft

  • 6ft

  • 8ft (optional)

  • Compactor - can be rented

  • Excavator- can be rented

  • Concrete saw- cutting blocks

  • Hammer & chisel

  • Sledgehammer

  • Pickaxe

  • Caulk gun- for adhesive to glue capstones



Gravel Selection

Choosing the right gravel will make all the difference in the quality and longevity of your retaining wall.

2 types of base gravel are used for retaining walls, one is gravel ranging in size from 1 inch to dust (411’s, crushed limestone, etc.) the other type being clean gravel: ranging from 1 inch to 1/4th inch gravel (no dust, 57’s, clean limestone). For years crushed limestone or a similar alternative was the standard for base material. It compacts like concrete and has proved itself for years. A newer, popular, and backed by industry leaders is using clean gravel with no dust. Better suited for the climate with freeze and thaw cycles, it doesn’t absorb water like crushed material. Thus it doesn’t shift nearly as much as crushed material that is essentially constantly moving. With clean gravel like 57’s, it is highly recommended to use a geotextile(filter fabric). This product keeps gravel from mixing with native materials and allows water to drain through.


Base Preparation

Arguably the most crucial part of your retaining wall construction project. Without a good base, your retaining wall is destined to fail (it could last for few years or more but will likely fail in the future). Good base preparation involves compacting the native soil as well as the base gravel to the proper density. Often contractors fall short at this point of installation. A common belief is a plate compactor is satisfactory for compacting but unfortunately, it is not so. Not having the proper compacting equipment will lead to a poor base (and ultimately wall failure).


  1. Excavate footer - footer depth can be figured by taking ½ the height of the retaining wall block plus 6 inches. At a minimum, you want half of your retaining wall buried beneath soil grade

  2. following painted guides

  3. Be careful to not excavate too much past desired depth

  4. Install gravel in 2 to 3-inch layers and compact, making a minimum of 3 passes with your compactor

  5. Larger compactors may be able to compact 6 inches of material or more at a time- see your compactors manual for suggestions

  6. Footer Drain- should be covered in cloth fabric to prevent sediment from entering

  7. Typically the footer drain is daylighted at one end (or both) of the wall and should extend 10 ft past the wall at a minimum

  8. In certain instances, face drains will need to be used.

Base Course

Now you have your base prepared and your block is on site. Now let’s start building the base course.

  1. Starting at your lowest point in the Retaining Wall lay your first block

  2. Every block in the base course needs to be level from left to right and front to back, as well as level to each other

  3. For straight walls, it is recommended to use a string line to keep the retaining wall straight

  4. Curved walls are more o