It’s not just ugly to see a retaining wall that leans, breaks, or falls after one wet season; it’s also a waste of time and money. You already know the problem if you want to develop one: soil erosion, yards that aren’t level, and slopes that make outdoor spaces unusable. Learning how to construct a retaining wall with blocks the right way means your wall stands firm for decades, not just a few seasons.
Here’s the good news. When done right, building concrete block retaining walls is one of the easiest hardscaping jobs to perform yourself. We’ll show you how to do everything in this guide, from excavating the base trench to putting the cap blocks in place. The main ideas remain the same, no matter how tall your wall is, whether it’s 2 feet or 6 feet.
What Is a Block Retaining Wall?
A block retaining wall is a structure built from concrete or masonry units designed to hold back soil on a sloped or graded surface. It prevents erosion, creates level outdoor areas, and adds structural definition to a landscape. Most residential block walls range from 2 to 6 feet in height.
Think of it like a dam for soil. Without it, gravity pulls everything downhill: your garden beds, your lawn, your topsoil. A well-built retaining wall keeps all of that in place while giving your yard a clean, finished look.
Block walls are preferred over timber or poured concrete for most DIY projects because they’re modular, affordable, and forgiving to install.
Types of Retaining Wall Blocks
Before starting your retaining wall block installation, you need to pick the right block. Not all blocks work the same way.
Concrete Segmental Blocks are the most popular option. They come with a locking lip or pin system that keeps each course from sliding forward under soil pressure. Allan Block is one of the most widely used brands in this category.
Dry-Stack Natural Stone works for shorter decorative walls but lacks the structural locking features of manufactured blocks. It’s not ideal for walls holding significant soil loads.
Tumbled or Textured Concrete Blocks offer a natural stone appearance with the strength of concrete. They’re great for walls where aesthetics matter.
For any wall over 3 feet, always choose a block with a built-in locking feature either a back lip, tongue and groove, or locking pin configuration.
Do You Need a Permit to Build a Retaining Wall?
Most places don’t need a permit for retaining walls that are less than 4 feet tall. You usually need engineering permission and a building permit for walls that are more than 4 feet high. Before you start, always check with your local government. Requirements vary by city, county, and soil type.
Some places lower this limit to 3 feet, especially close to property lines or public easements. If you get this wrong, you could have to knock down the whole wall. A straightforward call to your local building department takes 10 minutes and saves you months of trouble.
Step-by-Step Guide to Construct a Retaining Wall with Block
This is the core of what you came for. Following these retaining wall construction steps carefully skipping any of them is how walls fail.
Step 1: Mark and Excavate the Area
Start by staking out the wall’s front edge. Use marking paint or a string line to define the full length. For curved walls, a garden hose is a practical layout tool.
Excavate all surface vegetation and organic material from the area. Organic matter compresses over time it cannot be used as backfill. For walls 3 to 4 feet or taller, cut back into the hillside as far back as the wall is tall.
Step 2: Dig and Prepare the Base Trench
The base trench is where your wall either succeeds or fails. Dig it 24 inches wide and at least 6 inches deep, plus an extra 1 inch for every 1 foot of wall height. For walls under 4 feet, an 18-inch wide by 4-inch deep trench is acceptable.
Compact the trench with a minimum of two passes using a plate compactor. If you’re dealing with heavy clay or previously disturbed soil, remove it and replace it with compacted granular material in 8-inch lifts.
Step 3: Install the Gravel Base
Place a minimum of 6 inches of 3/4-inch crushed gravel (wall rock) in the trench. Rake it smooth and compact it with two passes of the plate compactor. Check the entire length for level before moving on.
This is your block retaining wall footing. It’s the foundation everything rests on. A level gravel base means every course above it stays manageable.
Step 4: Set the First Course of Blocks
The initial course of blocks is the most significant section of the whole wall. Every course following it follows its lead. If one is off, the whole wall is off. Put each block down with the raised front lip facing up and out. Always check the level from side to side and front to back.
Use a dead blow hammer to make little changes to blocks. Put up to 1/2 inch of coarse sand under a block if it is low. The first course should be buried about one block height below the finished grade.
Tilt the bricks back just a little bit toward the hill. Not a lot, just enough that the wall leans into the earth’s load instead of away from it.
Step 5: Install the Perforated Drain Pipe
Water is a retaining wall’s worst enemy. Saturated soil creates hydrostatic pressure that can push a wall over from behind. Place a 4-inch perforated drain pipe directly behind the first course at the lowest point of the trench.
Run the pipe to daylight every 50 feet and wrap it in non-woven filter fabric. Never use woven filter fabric here it restricts water flow and acts like a dam.
Step 6: Stack Blocks and Backfill Per Course
Stack each new course so the vertical seams are offset from the course below by at least one-quarter the block length. This is called a running bond and it’s what gives the wall its structural strength.
After each course, fill the hollow cores and 12 inches behind the blocks with wall rock. Then backfill behind the wall rock with approved on-site soils in lifts of no more than 8 inches. Compact with the plate compactor starting on top of the blocks and working backward.
Step 7: Install Geogrid Reinforcement (If Needed)
Geogrid is a mesh reinforcement material laid between block courses to stabilize the soil mass behind a retaining wall. It’s required for most walls over 3 to 4 feet tall or any wall retaining poor or clay-heavy soil.
Lay geogrid flat between courses and extend it back into the hillside for a distance equal to the wall’s total height. For a 6-foot wall, geogrid extends 6 feet behind the wall. Some grids are uniaxial meaning the strength only runs in one direction so make sure that direction points back into the hillside.
Geogrid works by connecting the wall to the soil mass behind it, moving the angle of repose deeper into the hillside and reducing the back pressure on the blocks.
Step 8: Cut Blocks When Needed
Cutting blocks is straightforward with the right tools. Use a masonry chisel and small sledgehammer for rough cuts, or an angle grinder with a diamond blade for clean, precise cuts. A concrete saw also works well for larger projects.
Always wear a respirator when cutting concrete. Concrete dust contains silica particles that are harmful to breathe.
Step 9: Install Cap Blocks and Adhesive
There is no weight above the top course of blocks to keep it in place. Before putting on the cap blocks, use a block-specific construction adhesive on the top of the second-to-last course. A two-part epoxy or a polyurethane-based adhesive works well. This keeps everything in place during heavy rain and freeze/thaw cycles.
Step 10: Final Backfill and Grading
Once drainage stone is backfilled to within 6 to 12 inches of the top of the wall, cover it with non-woven filter fabric and finish the last layer with good topsoil. This supports grass or plantings above the wall and directs surface water away from the blocks.
Avoid planting large shrubs or trees directly above taller walls. Root growth creates dynamic pressure that can damage the wall structure over time.
Cost to Build a Block Retaining Wall
Cost is usually the first question and a fair one.
| Wall Type | DIY Material Cost | Professional Install |
| 2-foot wall (per linear ft) | $15–$25 | $35–$55 |
| 4-foot wall (per linear ft) | $30–$50 | $70–$100 |
| 6-foot wall (with geogrid) | $60–$90 | $120–$180 |
DIY saves 40 to 60 percent on labor. But for walls over 4 feet, hiring a professional is worth considering especially if engineering approval is required.
Common Mistakes to Avoid
These are the seven most common errors that cause block retaining walls to fail early:
- Skipping proper base compaction The wall sinks and shifts.
- No drainage pipe Hydrostatic pressure builds and pushes the wall outward.
- Using organic backfill It compresses over time and leaves voids behind the wall.
- Not burying the first course The base course needs to be partially below grade.
- Ignoring geogrid requirements Taller walls need reinforcement or they lean.
- Running bonds not maintained Aligned seams create weak vertical lines through the wall.
- Using woven filter fabric restricts water flow and causes pressure buildup.
Tools and Materials Checklist
Before a single block goes in the ground, gather everything. Starting without the right tools halfway through is frustrating and costly.
Materials you’ll need:
- Concrete segmental blocks
- 3/4-inch crushed gravel (wall rock)
- Coarse sand (for minor base adjustments)
- Non-woven filter fabric
- 4-inch perforated drain pipe
- Geogrid (for walls over 4 feet)
- Block adhesive (for cap course)
- Topsoil (for final backfill layer)
Tools required:
- Plate compactor
- Dead blow hammer
- Long level (4-foot minimum)
- Masonry chisel and small sledgehammer or angle grinder with a diamond blade
- Shovel and tamper
- String line and stakes
- Marking paint
Need Expert Hardscaping in Whittier?
If this project feels bigger than a weekend DIY job, that’s completely understandable. Taller walls, difficult slopes, and drainage challenges are best handled by professionals who do this every day. Robert’s Complete Care offers expert hardscaping in Whittier with full design, installation, and drainage management. From small garden walls to large structural retaining projects, the team brings the skills to get it done right the first time.
Final Thoughts
Building a retaining wall out of concrete blocks is a project that pays off if you are patient and plan. If you get the base right, put in the right drainage, and follow all the steps to build the wall without cutting corners, it will last for decades. This guide has everything you need to do it yourself if you’re ready. Robert’s Complete Care can help you if the slope is steep, the wall is tall, or you just want it done perfectly without having to guess. Contact us today for a free consultation on professional hardscaping in Whittier. We’ll look at your site, explain your alternatives, and take care of everything from digging the hole to putting on the last cap block.
Frequently Asked Questions
What is the 1/3 rule for retaining walls?
The 1/3 rule states that one-third of a retaining wall’s total height should be buried below grade. So for a wall with 3 feet of visible height, the base should sit at least 1 foot underground. This buried portion provides the structural base that prevents sliding and overturning.
This rule gives the wall stability against the horizontal soil pressure pushing against it from behind.
How to build a retaining wall with blocks step by step?
Mark and excavate the area, compact a gravel base trench, install a level first course of blocks, add a perforated drain pipe, stack blocks with offset seams, backfill and compact per course, install geogrid if required, and finish with cap blocks and adhesive. That is how to construct a retaining wall with a block in its most direct form.
What are the 7 common mistakes made when installing retaining wall blocks?
The seven most common mistakes are: no base compaction, skipping drainage, using organic backfill, not burying the base course, ignoring geogrid requirements, aligned vertical seams, and using woven filter fabric. Each one reduces the wall’s structural integrity or lifespan.
What do you put under retaining wall blocks?
You put a layer of 3/4-inch crushed gravel, often called wall rock, under the bricks that hold the wall up. This layer needs to be at least 6 inches deep and completely level. It serves as the base, providing drainage and a firm, level surface for the base course.
When making little changes to the level, don’t utilize sand as the only base material.
Does a 2-foot retaining wall need a footing?
A 2-foot retaining wall does not need a concrete footing. A compacted gravel base of 4 to 6 inches is sufficient for low walls. However, the base trench still needs to be excavated and compacted properly skipping this step leads to settling and shifting over time.
