Want to learn how to build a retaining wall? Keep reading to 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 requires an engineer to design your 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, and Pavestone
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 failing.
Try not to disturb more soil than needed during excavation, if you do be sure to compact adequately.
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:
Shovels-(flat and pointed)
String line & stakes
torpedo(1ft or less)
3ft or 4ft
Compactor - can be rented
Excavator- can be rented
Concrete saw- cutting blocks
Hammer & chisel
Caulk gun- for adhesive to glue capstones
Most of the equipment and tools can be rented from your local Equipment Rental Yard.
Choosing the right gravel will make all the difference in the quality and longevity of your block 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 more recent, popular, and backed by industry leaders is using clean gravel with no dust. Better suited for climates with freeze and thaw cycles. Removing the dust from the gravel mixture 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.
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).
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
following painted guides
Be careful to not excavate too much past desired depth
Install gravel in 2 to 3-inch layers and compact, making a minimum of 3 passes with your compactor
Larger compactors may be able to compact 6 inches of material or more at a time- see your compactors manual for suggestions
Footer Drain- should be covered in cloth fabric to prevent sediment from entering
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
In certain instances, face drains will need to be used.
Now you have your base prepared and your block is on site. Now let’s start building the base course.
Starting at your lowest point in the Retaining Wall lay your first block
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
For straight walls, it is recommended to use a string line to keep the retaining wall straight
Curved walls are more open to interpretation- using things like a hose or extension cord can be good for a guide
Use a torpedo level for checking individual blocks
Use 3ft and larger to make sure your blocks are all level with each other
Check for any blocks not touching the level or blocks holding the level too high
Continue until the base course is completed
Install footer drain once the base course has been completed
If using face drains install those at the lowest point in the footer drain
Backfilling and Stacking
So your base course of block and footer drain is installed you can begin stacking retaining wall block and backfilling with clean ROUNDED 1-inch gravel. Not angular!
It is also highly recommended to use a filter fabric extending from the base gravel to near the top of the wall. Making sure the fabric is against the soil backing and gravel is against the retaining wall blocks.
Make sure the previous layer of blocks are clean from any debris- use brush or blower to clean each row before next course
Start stacking the next row of block overlapping the joints of the previous layer avoiding vertical joints lining up
This makes the wall sturdy and is very important
In certain cases, patterned block walls have differently sized pieces that will create areas where joints will match up commonly referred to as vertical joints
As you complete the next row, fill clean gravel behind the retaining wall and compact every layer
If using a hollow block fill the cores of the retaining wall blocks every layer
Use something on hand like a hammer handle to make sure gravel is worked down into cores
Repeat steps 1 through 3 until the retaining wall is reached the desired height
Walls that require geogrid should install them between the appropriate layers
Extending from near the face of the retaining wall block to the back of the retaining wall footer
Almost done with the retaining wall, now time for installing capstones. If you built a straight retaining wall then your work is likely cut out for you. If you built a curved wall, you may have a bit of marking and cutting in your future. Some if not most retaining wall blocks are tapered in design, allowing you to curve walls easily to some degree. Likewise, the capstones are tapered as well. But, if your wall is a sharper curve or softer curve than the designed taper, you will have to mark and cut your blocks accordingly to meet the needs of your curve. We thought a video would be best to describe the marking and cutting of capstones. Check it out here
After marking and cutting the retaining wall capstones you are almost ready to adhere them to the retaining wall blocks with concrete adhesive or similar all-weather construction grade adhesive. Dry fit your capstones first to make sure they all fit together nicely. Proceed with adhesive once approved.
Finishing off your Retaining Wall Project
After you have finished the capstones, you can finish the backfilling and clean up process. The backfill gravel should be covered with a filter fabric to try and prevent as much sediment as possible from entering the gravel backfill zone.
Avoid planting large trees and bushes near the base or backfill zone to avoid problems with roots
Grass and shallow growing landscaping would be best near the wall and larger species kept at a distance
Be very picky with your base preparation and installation of the base course of retaining wall blocks. If you show discipline in these stages the rest will be much easier. Make sure you have adequate drainage gravel behind your retaining walls (minimum 18inches) and the footer drain is installed properly (directed away from the retaining wall base). Built to these guidelines your retaining wall installation projects should last for many years to come.
Be sure to check in for more blog posts to come, we will be diving into more of these topics in-depth.
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