DIY Concrete Blocks Retaining Wall: Step-by-Step

Constructing a concrete blocks retaining wall on your property can solve soil erosion problems and enhance your landscape’s aesthetic appeal. Allan Block, a popular manufacturer of retaining wall systems, provides resources that can aid in the successful completion of your project. Utilizing tools such as a level ensures that each block is perfectly aligned, which is vital for the wall’s structural integrity and longevity. Many homeowners have successfully undertaken this project, drawing inspiration from experts and online tutorials to guide them through each phase of the construction.

Retaining walls are more than just landscape features; they are essential structures that combat soil erosion and elegantly manage grade changes, transforming challenging landscapes into usable and beautiful spaces.

In essence, a retaining wall is a structural marvel designed to hold back soil, preventing it from sliding or collapsing. This is particularly crucial in sloped yards where gravity relentlessly pulls earth downward.

By counteracting this force, retaining walls create level terraces for planting, patios, or even driveways. This transforms otherwise unusable land into functional areas.

The Allure of the DIY Approach

The prospect of building your own retaining wall is appealing for several reasons.

First and foremost, significant cost savings can be realized by bypassing professional labor costs. The expense for materials is predictable, and you control the overall outlay.

Beyond the financial advantages, a DIY project grants you unparalleled customization. You can tailor the wall’s design, materials, and finish to perfectly complement your home and personal style.

There’s also the immense personal satisfaction derived from creating something substantial and enduring with your own hands. It’s a tangible accomplishment that enhances your property and fosters a sense of pride.

Navigating the Red Tape: Permits and Building Codes

Before you even dream of laying the first block, there’s a crucial step that cannot be overlooked: consulting your local building codes and obtaining the necessary permits. This isn’t merely a suggestion; it’s an absolute requirement.

Why Permits Matter

Local building codes are in place to ensure the safety and structural integrity of any construction project, including retaining walls. They dictate factors such as maximum wall height without engineering oversight, setback distances from property lines, and drainage requirements.

Failing to comply with these regulations can lead to serious consequences, including hefty fines, legal complications, and even the mandatory reconstruction of your wall.

Imagine investing time, effort, and money into a project, only to be forced to tear it down and start over because you neglected to obtain the proper permits.

How to Ensure Compliance

Your first step should be to contact your local building department or planning office. Inquire about the specific requirements for retaining walls in your area.

Be prepared to provide details about your project, including the proposed wall height, location, and materials. They will guide you through the permit application process and ensure you understand all applicable regulations.

Taking the time to navigate the bureaucratic landscape upfront will save you considerable headaches down the road. It ensures your project is not only aesthetically pleasing but also structurally sound and legally compliant, setting the stage for a successful and worry-free DIY endeavor.

Phase 1: Planning and Preparation for Success

Retaining walls are more than just landscape features; they are essential structures that combat soil erosion and elegantly manage grade changes, transforming challenging landscapes into usable and beautiful spaces.

In essence, a retaining wall is a structural marvel designed to hold back soil, preventing it from sliding or collapsing. This is particularly crucial in sloped yards or areas prone to erosion. Before you even think about laying the first block, a comprehensive planning and preparation phase is absolutely vital. This isn’t just about buying materials; it’s about understanding your site, calculating your needs, and equipping yourself for success. Skimping on this phase is a recipe for frustration, wasted resources, and a potentially unstable wall.

Site Assessment: Understanding Your Landscape

The very first step in any successful retaining wall project is a thorough assessment of your build site. You must know your enemy (the landscape) before you can conquer it. This involves understanding the soil, drainage patterns, existing vegetation, and potential challenges.

Soil Type Identification

Different soil types have different properties that affect drainage, compaction, and overall stability. Sandy soils drain well but may not compact effectively. Clay soils hold water and can expand and contract, potentially putting pressure on the wall. Loamy soils are generally ideal.

To determine your soil type, perform a simple soil texture test. Grab a handful of moist soil and try to form it into a ball. If it crumbles easily, it’s likely sandy. If it forms a sticky ball, it’s clay. If it’s somewhere in between, you likely have loam. You can also send a soil sample to a local agricultural extension office for a professional analysis.

Drainage Considerations

Proper drainage is paramount for the longevity of your retaining wall. Water buildup behind the wall can create hydrostatic pressure, which can eventually cause the wall to bulge, crack, or even collapse. Observe how water flows across your property during rainstorms.

Identify areas where water tends to collect. Ensure that your retaining wall design incorporates adequate drainage, such as a gravel backfill and a perforated drain pipe at the base of the wall.

Vegetation Removal and Management

Clear the build site of all vegetation, including grass, weeds, shrubs, and small trees. Remove the root systems as well, as they can interfere with the foundation. Consider the impact of nearby large trees.

Their roots can extend far and wide, potentially undermining the wall’s stability or making excavation difficult. You may need to consult with an arborist to determine the best course of action.

Determining Wall Height and Length

Accurately measure the height of the slope you need to retain. This will determine the necessary wall height. It’s often better to build slightly higher than necessary to account for settling and future erosion.

Measure the length of the area you need to retain. This will determine the required wall length. It’s crucial to get these measurements right to avoid material shortages or unnecessary waste.

Identifying Potential Challenges

Before you start digging, check for underground utilities such as gas lines, water pipes, and electrical cables. Contact your local utility companies to locate and mark these utilities before you begin any excavation. This is a critical safety precaution.

Also, be aware of any large tree roots that may be present in the build site. You may need to reroute the wall or carefully excavate around the roots to avoid damaging the trees.

Material Calculation: Getting the Numbers Right

Accurate material calculation is essential for cost control and project efficiency. You don’t want to run out of materials halfway through the job, and you don’t want to overbuy and end up with a pile of unused blocks.

Calculating Concrete Blocks (CMUs)

Measure the dimensions of the Concrete Blocks (CMUs) you plan to use. Use these dimensions and your total wall length and height measurement to determine the number of blocks you will need for each course (row). Add an additional 5-10% for waste due to cuts and potential breakage.

Account for any overlaps in the blocks’ design and factor those into your calculations. For example, with standard blocks of dimensions 8"x8"x16", you may need 7 to 8 blocks per linear foot of wall. Be sure to measure correctly so you are not short by the end of the project.

Estimating Gravel and Sand

Gravel is used for drainage behind the wall, and sand is used for creating a level base. To calculate the amount of gravel needed, multiply the wall’s length by its height and by the desired width of the gravel backfill (usually 1 foot). This will give you the volume of gravel needed. Divide that number by 27 to convert to cubic yards.

To calculate the amount of sand needed, multiply the wall’s length by the width of the base and by the desired depth of the sand layer (usually 2-4 inches). Convert the result to cubic yards.

Geogrid Calculation (If Needed)

Geogrid is a reinforcing material used for taller walls to provide additional stability. Consult with a structural engineer or a retaining wall specialist to determine if geogrid is needed for your project.

If geogrid is required, the length and spacing will depend on the wall’s height, soil conditions, and the type of geogrid used. A general rule of thumb is that the geogrid should extend back into the soil a distance equal to at least 60% of the wall’s height. The vertical spacing between layers of geogrid typically ranges from 1 to 3 feet.

Tool and Material Acquisition: Gearing Up for the Build

Having the right tools and materials on hand will make the construction process much smoother and more efficient. Before you start, ensure you have everything you need to avoid frustrating delays.

Essential Tools

• Shovel and Spade: For digging and moving soil.
• Wheelbarrow: For transporting materials.
• Level (Spirit Level, Laser Level): For ensuring the wall is level and plumb. A laser level can be particularly helpful for long walls.
• String Line (Mason’s Line): For maintaining a straight line.
• Measuring Tape: For accurate measurements.
• Rubber Mallet: For gently adjusting the blocks.
• Hand Tamper (Plate Compactor): For compacting the base materials. A plate compactor is recommended for larger projects.
• Circular Saw or Masonry Saw: For cutting blocks (if necessary).

Safety Gear

• Gloves: To protect your hands.
• Safety Glasses: To protect your eyes from debris.
• Ear Protection: Especially when using power tools.
• Knee Pads: To protect your knees during prolonged kneeling.
• Work Boots: To protect your feet.

Purchasing Materials

Purchase your materials from reputable Home Improvement Stores or Landscape Supply Yards. Compare prices and quality before making a purchase. Don’t be afraid to ask for discounts, especially when buying in bulk.

When selecting Concrete Blocks (CMUs), look for blocks that are uniform in size and free from cracks or chips. Choose gravel that is clean and well-graded. Ensure the sand is paver sand or leveling sand, as it is designed for creating a smooth, compact base.

By investing the necessary time and effort into planning and preparation, you’ll set yourself up for a successful and rewarding retaining wall project. This initial phase is not just about gathering materials; it’s about building a solid foundation for your entire endeavor, ensuring that the final result is both structurally sound and aesthetically pleasing.

Phase 2: Foundation Construction – Laying the Groundwork

Phase 1 meticulously prepared the ground, setting the stage for the crucial next step: building the foundation. This phase is the cornerstone of your retaining wall project. A well-constructed foundation ensures stability, longevity, and prevents future headaches. Let’s delve into the details of excavation, base preparation, and laying the first course – the critical elements that will support your wall for years to come.

Excavation: Digging the Trench

The excavation stage is where you physically define the footprint of your retaining wall. Precision here is paramount.

1. Depth Matters: Begin by digging a trench along the marked line. The depth must accommodate the base materials (gravel and sand) plus a portion of the first course of blocks. A general rule is to dig down at least 6-8 inches, but this depends on your soil conditions and the height of your wall.
2. Width for the Win: The trench needs to be wider than the blocks themselves, typically by about 6-12 inches on each side. This extra space allows for proper compaction of the gravel backfill, ensuring good drainage behind the wall. Measure your block width and add the extra allowance to calculate the total trench width.
3. Sloping for Success: Slight backward slope is essential for effective drainage. The trench bottom should slope gently away from where the wall will stand. This ensures that water flows away from the wall’s base, preventing hydrostatic pressure buildup that could compromise its structural integrity. Use a level to periodically check the slope as you dig.
4. Debris Removal: Clear the trench of all debris: rocks, roots, and organic matter. A clean trench bottom provides a stable base for the gravel layer.

Base Preparation: Creating a Solid Foundation

With the trench excavated, you’ll now lay the groundwork for a stable, well-drained base.

1. Landscape Fabric First: Start by lining the trench with Landscape Fabric (Filter Fabric). This seemingly simple step is crucial. It prevents soil particles from migrating into the gravel base, clogging the drainage system and undermining the foundation over time. Overlap the edges of the fabric to ensure full coverage.
2. Gravel Layer: The Drainage Workhorse: Pour a layer of Gravel (Crushed Stone, Base Gravel) into the trench. Aim for a thickness of at least 4-6 inches. Use gravel that is about 3/4 inch in size.
3. Compaction is Key: Compact the gravel thoroughly using a hand tamper or plate compactor. Compaction is critical for creating a dense, stable base.
4. Sand Layer: The Leveling Agent: Spread a layer of Sand (Paver Sand, Leveling Sand) over the compacted gravel. The sand layer is typically 1-2 inches thick. The primary goal is to create a smooth and perfectly level surface for the first course of blocks. Use a level and a long screed board to achieve a perfectly even plane.
5. Recompact the Sand: Lightly compact the sand layer to settle it and ensure a firm surface.
6. Check Again!: Double-check the levelness of the sand layer with a level before proceeding to the next step. Any imperfections at this stage will be magnified in subsequent courses.

First Course Installation: The Foundation’s Cornerstone

Laying the first course of blocks is arguably the most critical step in the entire project. It sets the foundation for everything that follows.

1. Precision Placement: Carefully place each Concrete Block (CMU) onto the prepared sand bed. This course MUST be perfectly level, both horizontally and vertically.
2. Laser Level Advantage: If you have access to a laser level, now is the time to use it. A laser level projects a perfectly horizontal line, making it easier to ensure consistent levelness across the entire course.
3. Rubber Mallet Adjustments: Use a Rubber Mallet to gently tap the blocks into place and make fine adjustments. Avoid using excessive force, as this could damage the blocks.
4. Check for Levelness Constantly: After placing each block, check for levelness using a spirit level. Place the level both along the top of the block and along its front face to ensure it’s level in both directions.
5. Correcting Imperfections: If a block is not level, add or remove sand beneath it until it is perfectly aligned. Take your time and be meticulous.
6. Continuous Evaluation: As you lay each subsequent block in the first course, continuously check the levelness and alignment relative to the previous block. This ensures that any minor imperfections are corrected before they accumulate and cause problems later on.
7. Consistent Gaps: Leave small, consistent gaps between blocks as specified by the block manufacturer. These gaps allow for drainage and accommodate slight expansion and contraction due to temperature changes.

By meticulously following these steps, you’ll establish a solid foundation for your retaining wall, ensuring its long-term stability and visual appeal. With a robust foundation in place, you’re well-prepared to continue building your retaining wall with confidence!

Phase 3: Wall Construction – Building Upwards

Phase 2 laid the groundwork with a solid foundation, now it’s time to build the wall itself. This phase demands precision, patience, and a keen eye for detail. Correctly stacking the blocks, incorporating geogrid when necessary, ensuring adequate drainage, and creating a batter are all critical for a retaining wall that stands the test of time. Let’s break down each step.

Stacking Blocks: Achieving Alignment and Stability

The art of stacking blocks may seem simple, but it’s where the structural integrity of your wall is truly forged. Each block must be placed with careful attention to alignment and levelness. Deviations, however small, can accumulate and compromise the wall’s stability.

The Importance of Levelness and Alignment

Use your Level (Spirit Level, Laser Level) relentlessly. Check each block horizontally and vertically as you place it. A laser level, while an investment, is highly recommended for its precision and ease of use, especially for longer walls. Run a String Line (Mason’s Line) along each course to ensure consistent horizontal alignment. Correct any minor imperfections immediately with a Rubber Mallet.

Enhancing Stability with Construction Adhesive

For walls exceeding three feet in height, or in areas prone to seismic activity, Construction Adhesive (Masonry Adhesive) is a worthwhile investment. Apply a generous bead of adhesive to the top surface of each block before placing the next course. This creates a strong bond between layers, preventing shifting and adding significant stability. Look for adhesives specifically designed for masonry applications, ensuring compatibility and long-term durability.

Staggering Joints: A Cornerstone of Strength

Staggering the joints between block courses, much like bricklaying, is essential. This technique, where vertical joints are offset from one course to the next, prevents continuous vertical cracks and distributes stress more evenly throughout the wall. Aim for a minimum overlap of one-third the block’s length. This simple measure significantly enhances the wall’s overall strength and resistance to lateral forces.

Geogrid Installation (If Needed): Reinforcing the Wall

Geogrid is a high-strength synthetic mesh used to reinforce the soil behind the retaining wall, creating a composite structure that’s far stronger than the wall alone. Its use is generally recommended for walls exceeding four feet in height, or in situations where the soil is unstable.

Determining Geogrid Length and Spacing

Consult a local engineer or refer to the retaining wall block manufacturer’s specifications to determine the appropriate length and vertical spacing of the geogrid. These calculations will be based on factors such as wall height, soil type, and slope angle. Never underestimate this step, as incorrect geogrid placement can render it ineffective.

Securing Geogrid to the Blocks

The geogrid must be securely connected to the retaining wall blocks to transfer the tensile forces from the soil to the wall facing. Most block systems have designated slots or connectors for geogrid placement. Ensure the geogrid is properly tensioned and anchored before backfilling. A loose or poorly connected geogrid will not provide adequate reinforcement. Follow the manufacturer’s instructions meticulously.

Drainage Considerations: Managing Water Flow

Water is the enemy of retaining walls. Poor drainage can lead to hydrostatic pressure buildup, which can eventually cause the wall to bulge, crack, or even collapse. Proper drainage is therefore paramount.

Backfilling with Gravel: Promoting Water Flow

Behind the wall, backfill with Gravel (Crushed Stone, Base Gravel) to create a free-draining zone. Use gravel that is clean and angular, typically ¾ inch to 1 ½ inches in size. Backfill in layers, compacting each layer thoroughly to prevent settling. The gravel should extend at least one foot behind the wall.

Installing a Perforated Drain Pipe

At the base of the wall, install a perforated drain pipe to collect and channel water away from the structure. The pipe should be surrounded by gravel and sloped slightly to ensure positive drainage. Connect the drain pipe to a suitable outlet, such as a storm drain or daylight drain.

Preventing Clogging: Protecting the Drainage System

To prevent soil from clogging the drainage system, wrap the drain pipe and the gravel backfill with Landscape Fabric (Filter Fabric). This fabric allows water to pass through while preventing soil particles from entering and clogging the system. Regularly inspect and clear any debris that may accumulate near the drainage outlets.

Batter (Wall Batter, Setback): Angling for Stability

A batter, or setback, refers to the slight backward incline of the wall. This angle, though subtle, significantly increases the wall’s stability by counteracting the force of the soil pushing against it.

Creating the Batter Angle

There are several ways to achieve a batter. One method is to use blocks specifically designed with a built-in setback. Another is to manually offset each course of blocks slightly backward as you build. The amount of setback will depend on the wall height and design, but typically ranges from ¼ inch to ½ inch per course. Consult with the block manufacturer’s specifications or a qualified engineer for guidance on the appropriate batter angle for your specific project. By carefully considering and implementing each of these elements, you’ll be well on your way to building a retaining wall that is not only functional and aesthetically pleasing, but also built to last.

Phase 4: Finishing Touches – Completing the Project

Phase 3 saw the walls rising steadily, block by block. Now, it’s time to put the finishing touches on your retaining wall, transforming it from a construction project into a landscape feature. This phase focuses on backfilling for stability and aesthetics, capping the wall for a polished appearance, and ensuring a level, clean finish.

These final steps are just as crucial as the earlier ones, as they contribute significantly to both the wall’s functionality and its visual appeal. Let’s explore how to execute each element with precision and care.

Backfilling: Filling Behind the Wall for Stability and Growth

Backfilling is more than just filling a gap; it’s about providing crucial support and creating a suitable environment for plant life. Proper backfilling prevents soil erosion and ensures the wall’s long-term stability. It’s a process that requires careful layering and compaction.

Layering and Compaction: The Keys to Success

Begin by backfilling with gravel immediately behind the wall. This layer acts as a drainage medium, allowing water to flow freely and preventing hydrostatic pressure from building up against the wall.

Compact the gravel in layers, using a hand tamper or plate compactor, to ensure it’s dense and stable.

Next, add a layer of topsoil above the gravel. Choose a high-quality topsoil rich in organic matter to promote healthy plant growth if you plan on planting near the wall. Again, compact the topsoil in layers to prevent settling.

Choosing the Right Topsoil

Selecting the right topsoil is essential for plant health. Look for a mix that balances drainage and moisture retention.

A sandy loam topsoil is generally a good choice, as it provides good drainage while still retaining enough moisture to support plant growth. Consider adding compost or other organic amendments to further enrich the soil.

Sloping for Optimal Drainage

Finally, slope the backfill away from the wall to encourage water runoff. This prevents water from pooling behind the wall and reduces the risk of erosion.

A gentle slope of about 5% is usually sufficient. This seemingly small detail can make a big difference in the longevity and stability of your retaining wall.

Capping Stones: Adding a Finished Look and Protecting Your Investment

Capping stones not only provide a polished, professional finish but also protect the top of the wall from water infiltration. Water can seep into the wall’s structure, causing damage over time. Capping stones act as a barrier, preventing this from happening.

Selecting Complementary Capping Stones

Choose capping stones that complement the overall aesthetic of your wall and landscape. Consider the color, texture, and size of the stones.

They should be wide enough to overhang the wall slightly, providing a drip edge that directs water away from the wall’s surface.

Local home improvement stores or landscaping suppliers offer a wide array of options.

Securing the Capping Stones with Adhesive

To ensure long-lasting durability, secure the capping stones with a high-quality construction adhesive. Apply a bead of adhesive to the top of each block, then carefully place the capping stone on top.

Press firmly to ensure good adhesion. This will prevent the stones from shifting or becoming dislodged over time.

Final Leveling: Ensuring a Uniform Surface

A level top surface is not just aesthetically pleasing; it also ensures stability and prevents water from pooling on the wall. Use a level to check the entire length of the wall and make any necessary adjustments.

Slight imperfections can be corrected by adding shims or adjusting the placement of the capping stones. Attention to detail at this stage will pay off in the long run.

Site Cleanup: Leaving a Tidy Workspace

Finally, take the time to clean up the work site. Remove all excess materials, tools, and debris. Leaving a tidy workspace is not just a matter of aesthetics; it’s also a matter of safety.

Ensure that all materials are properly disposed of or stored. A clean and organized site is a safe site. Take pride in your work and leave the area looking its best.

Phase 5: Inspection and Maintenance – Protecting Your Investment

Phase 4 brought the project to its aesthetically pleasing conclusion, the true test of longevity begins. Now, vigilance and proactive care become paramount. This phase isn’t about the thrill of construction, but about safeguarding your hard work. It’s about ensuring that your retaining wall stands strong and beautiful for years to come.

We must protect the integrity of your investment through rigorous inspection and proactive maintenance practices. This is more than just "checking" the wall every now and then; it’s about establishing a routine that identifies potential issues before they escalate into costly repairs or structural compromises. Let’s break down what this entails:

Schedule Inspection with Building Inspector: Ensuring Compliance and Safety

It’s a significant milestone to complete a DIY project of this scale; however, it’s vital to make certain the work complies with regulatory standards. Contacting your local building inspector is a critical step, not only for legal compliance but also to gain an expert’s perspective on the wall’s structural integrity.

Why is this necessary? Building codes are in place to ensure safety and prevent potential hazards. An inspector can identify any deviations from these codes, which might otherwise go unnoticed.

The Inspection Process: What to Expect

The inspection process typically involves a review of the wall’s construction against the approved plans and local building codes. The inspector will examine several aspects:

• Foundation: Ensuring the foundation is properly constructed and meets depth and material requirements.
• Wall Alignment: Verifying the wall is straight, level, and has the correct batter angle (if applicable).
• Drainage: Checking that the drainage system is installed correctly and functioning effectively.
• Materials: Confirming that the materials used are compliant with local regulations.

Be prepared to provide any documentation related to the project, such as permits, plans, and material specifications. A successful inspection provides peace of mind and ensures that your retaining wall meets the required safety standards.

Regular Inspection and Maintenance: A Proactive Approach

Waiting for a problem to surface is not a sound maintenance strategy. Regular inspections are a preemptive strike against potential issues. These routine check-ups allow you to identify and address minor problems before they become major headaches, saving you significant time and money in the long run.

What to Look For

During your regular inspections, pay close attention to the following:

• Shifting or Leaning: Is the wall tilting or moving in any direction? This could indicate foundation issues or soil instability.
• Cracking: Are there any cracks in the blocks or mortar joints? Cracks can weaken the wall’s structure and allow water to penetrate.
• Water Damage: Are there signs of water damage, such as efflorescence (white, chalky deposits) or erosion? Water can deteriorate the wall’s materials over time.
• Vegetation Growth: Are there any plants growing in or around the wall? Roots can damage the structure and compromise its integrity.

Addressing Potential Problems

If you spot any of these issues, don’t ignore them. Take immediate action to address them. Small cracks can be filled with masonry sealant, vegetation can be removed, and drainage problems can be addressed by clearing obstructions.

For more significant issues, consult with a qualified contractor or engineer. Early intervention is key to preventing further damage and preserving the wall’s stability.

Maintaining Proper Drainage: Preventing Water Damage

Water is the unseen enemy of retaining walls. Improper drainage can lead to water buildup behind the wall, creating hydrostatic pressure that can cause it to bulge, crack, or even collapse. Maintaining a functional drainage system is therefore of utmost importance.

Clearing Debris

Regularly inspect and clear any debris from drainage outlets, such as weep holes or drain pipes. Leaves, soil, and other materials can clog these outlets, preventing water from escaping and leading to pressure buildup.

Ensuring Effective Drainage

Make sure the ground behind the wall slopes away from the structure to facilitate water runoff. If you notice any areas where water is pooling, take steps to improve drainage in those areas.

This might involve adding more gravel, installing additional drainage pipes, or regrading the soil. The goal is to ensure that water is efficiently channeled away from the wall, minimizing the risk of water damage and structural failure.

By diligently following these inspection and maintenance guidelines, you can ensure that your retaining wall remains a strong, functional, and beautiful part of your landscape for years to come. This continuous commitment to proactive care will not only protect your investment but also provide lasting peace of mind.

So, there you have it! Building your own concrete blocks retaining wall might seem a bit daunting at first, but with a little elbow grease and these steps, you’ll be enjoying a beautiful and functional wall in no time. Don’t be afraid to get your hands dirty and remember to double-check those measurements! Good luck with your concrete blocks retaining wall project!