Build Your Own Concrete Block Retaining Wall

How to Build a Concrete Block Retaining Wall That Lasts for Decades

When I built my first concrete block retaining wall, I thought it would be a simple weekend project. Dig a trench, stack some blocks, and call it a day right?

Well… that couldn’t be further from the truth.

In reality, building a retaining wall that actually holds back soil without leaning, cracking, or collapsing takes more planning and attention to detail than most people realize. The good news? If you follow the right steps from the start, your wall can last 50+ years with very little maintenance.

This guide walks you through everything I learned: the good, the bad, and the “wish I knew before I started.” Whether you’re holding back a small garden slope or creating a tiered backyard, these steps will save you time, money, and headaches.

Why Choose Concrete Blocks for a Retaining Wall?

Before we get into the how-to, let’s talk about the why.

Manufactured concrete blocks are:

• Strong – They can withstand tons of pressure from soil and water.
• Durable – They don’t rot like wood or break down like some stone mortars.
• Uniform – Every block is the same size, making it easier to get a straight, level wall.
• Low-maintenance – Once it’s up, you won’t have to mess with it much.
• Easy to work with – The blocks are free standing and do not require mortar.

And here’s a big one: concrete block walls are modular. You can add to them later or tie them into other landscaping projects. I’ve built wood walls and natural stone walls, and while they look nice, nothing beats the strength and longevity of a properly built concrete block wall.

Step 1: Planning and Design

Why it matters: A retaining wall isn’t just landscaping, it’s a structure that has to handle lateral pressure from soil and water. If you skip the planning stage, you might build something that looks fine at first but slowly leans or cracks over time.

Key things to decide before you start:

1. Height of the wall – Walls under 4 feet usually don’t require engineering or permits (check your local code), but anything taller may need special reinforcement or approval.
2. Length and layout – Will it be straight, curved, or stepped? Mark it out with spray paint or garden hose.
3. Drainage plan – Without proper drainage, even the strongest wall can fail. Decide now where water will go.
4. Block type – Choose between split-face decorative blocks or interlocking retaining wall blocks with a lip for easy stacking.
5. Reinforcement – For higher walls, consider rebar and filled cores for added strength.

Pro tip: Measure twice, buy once. Get your final measurements and then purchase 10% more blocks than you think you’ll need to account for cuts, mistakes, or future repairs.

Step 2: Gathering Tools and Materials

Here’s a basic list for most walls under 4 feet:

Materials

• Concrete retaining wall blocks
• Crushed stone or gravel (¾” clean stone is ideal)
• Paver base or road base mix
• Drainage pipe (perforated, with a sock if possible)
• Landscaping fabric
• Concrete mix (for footings if needed)
• Rebar (if reinforcing)
• Cap blocks (for the top row)
• Masonry adhesive (for corner blocks and caps)

Tools

• Shovels
• Pickaxe or mattock (for hard soil)
• Wheelbarrow
• Level (2’ and 4’)
• String line & stakes
• Rubber mallet or dead blow hammer
• Tape measure
• Circular saw or block splitter with masonry blade. A demo saw is a great option.
• Tamper or plate compactor

Step 3: Excavation

Why it matters: Your wall is only as strong as its foundation. If you rush this step, the wall will settle unevenly and eventually fail.

Process:

1. Mark the area – Use stakes and string to define the front and back of the trench.
2. Dig the trench – The depth should be about 1″ for every 8″ of wall height plus at least 6″ for the gravel base. For example, a 3-foot wall needs about 10–12″ deep trench.
3. Widen the trench – It should be wide enough to fit the block plus at least 6″ behind it for gravel drainage.

If your wall is many feet long, I’d recommend renting a machine such as a skid steer or small excavator. There is a lot of shoveling for one or two people and it makes more sense to use a machine rather than shovel fill and stone for days.

Pro tip: The first course (row) should be buried about 10% of the wall’s height to anchor it in place. For a 3-foot wall, bury the first 4–6 inches.

Step 4: Creating the Base

This is where most DIY retaining walls fail, they skip compacting or use the wrong material.

Steps:

1. Add 4–6 inches of crushed stone or paver base to the trench.
2. Use a hand tamper or plate compactor to compress it until it’s rock solid.
3. Check for level side-to-side and front-to-back. Any unevenness here will be multiplied as you stack blocks.

Why crushed stone, not sand?

Stone locks together better and doesn’t wash away as easily. Sand can shift over time, especially with water flow.

Step 5: Laying the First Course

This is the most important row you’ll lay so take your time with this step.

1. Place the first block at the lowest point of your trench. This ensures the rest of the wall steps up naturally if the ground slopes.
2. Level the block front-to-back and side-to-side. Tap it into place with a rubber mallet.
3. Add the next block and check level with the previous one. Adjust the base material under each block as needed.
4. Continue the first course, checking level and straightness every 2–3 blocks.

Pro tip: For curves, use smaller blocks or cut blocks with a masonry saw for cleaner joints.

Step 6: Backfilling and Drainage

Drainage is what keeps your wall standing for decades. Without it, water builds up behind the wall, increasing pressure and causing cracks or bulging.

Here’s how to do it right:

1. Lay landscaping fabric behind the first course, extending up the height of the wall. This prevents soil from clogging the gravel.
2. Place perforated drain pipe at the base, sloping slightly (1″ drop every 4–8 feet) toward an outlet or daylight.
3. Backfill with clean crushed stone up to about 12″ behind the wall.
4. Fold the landscaping fabric over the top of the gravel before adding soil — this keeps it free-draining.

Step 7: Building Up the Wall

1. Offset the joints of the second course so they don’t line up with the first (like bricks).
2. For interlocking blocks, pull them forward until the lip locks over the course below.
3. After each course, backfill with gravel and compact lightly.
4. Keep checking for level every 2–3 blocks.

If your wall is taller than 3 feet, insert vertical rebar into the block cores and fill with concrete every few feet for added strength.

Step 8: Capping the Wall

Caps give the wall a finished look and help lock the top row in place.

1. Dry-fit the cap blocks first to see where cuts will be needed.
2. Use masonry adhesive to secure each cap block to the course below.
3. Press firmly and let the adhesive cure as recommended before putting any load on the wall.

Step 9: Final Grading and Landscaping

1. Grade the soil on the uphill side so it slopes gently away from the wall — this helps water run off instead of pooling.
2. Add topsoil and plant grass, flowers, or shrubs as desired.
3. Mulch around plants to reduce erosion.

Stats: The Investment Side of Building It Yourself

Let’s look at a quick breakdown for a 20-foot-long, 3-foot-high wall:

Item	Cost (DIY)	Cost (Contractor)
Blocks & caps	$4000	$6000
Gravel & base	$150	Included in markup
Drainage materials	$75	Included in markup
Tools (rental/purchase)	$100	Included in markup
Labor	Free	$10,000+
Total	$	$16,000–$22,000

By doing it yourself, you could save $15,000+ and end up with a wall that’s every bit as solid provided you follow each step carefully.

Final Takeaway

A concrete block retaining wall is one of those projects that looks intimidating at first, but once you break it down into steps, it’s completely doable for a determined DIYer.

The key is patience and precision:

• Get the base level.
• Install proper drainage.
• Take your time on the first course.

Do it right, and you’ll have a structure that not only holds back soil but also boosts your property’s curb appeal and value for decades to come.

If you’re considering tackling a wall project, feel free to reach out or drop a comment — I’m always happy to share what worked (and what didn’t) from my own builds.