How to Build a Retaining Wall: Equipment, Materials, and Step-by-Step Guide

By the team at Beehive Rental & Sales — Serving Southern Utah's contractors and homeowners since 1994.

A well-built retaining wall does two things: it holds back earth and it lasts decades without shifting, cracking, or leaning. The difference between a wall that performs and one that fails almost always comes down to what happens below grade --- the base preparation, the drainage, and the compaction that nobody sees after the project is finished. This guide walks you through the entire process, from planning through cap placement, with specific equipment recommendations and mistakes to avoid.

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Quick Answer: Building a retaining wall requires proper base excavation, compacted gravel footing, drainage behind the wall, and course-by-course backfill compaction. For walls over 3 feet, a mini excavator and plate compactor are essential --- not optional. BeeHive Rental & Sales in St. George rents all the equipment you need for retaining wall projects. Call (435) 628-6663 for availability and project-specific recommendations.

Key Takeaways

• •Drainage is the #1 factor in retaining wall longevity --- over 90% of wall failures trace back to water pressure buildup behind the wall, not structural weakness
• •Walls over 3 feet require engineered equipment --- a mini excavator for base excavation and a plate compactor for each course of backfill are not shortcuts, they are requirements
• •Southern Utah's caliche soil layers can sit 12-18 inches below grade, requiring adjustments to your footing depth and sometimes a concrete saw to cut through
• •DIY retaining walls cost $15-$25 per square foot of wall face versus $25-$50 per square foot for professional installation, making rental equipment a significant cost saver
• •Browse retaining wall equipment at BeeHive --- plate compactors, mini excavators, concrete saws, and more available for daily or weekly rental

Understanding Retaining Wall Types

Before you pick up a shovel or rent a machine, you need to choose the right wall type for your project. Each type has different structural characteristics, material costs, and equipment requirements.

Segmental Block Walls (Most Common for DIY)

Segmental retaining wall blocks --- the interlocking concrete blocks you see at home improvement stores --- are the most popular choice for homeowner projects. They require no mortar, stack with a built-in setback for structural stability, and come in various sizes and textures.

Best for: Walls up to 4 feet (without engineering), garden terraces, landscape borders, raised beds.

Typical cost: $10-$15 per square foot for materials alone.

Gravity Walls (Natural Stone or Boulders)

Gravity walls rely on sheer mass to resist soil pressure. Natural stone or large boulders are stacked with a backward lean, and the weight of the stone itself holds back the earth. These walls have a more natural, rugged appearance that fits Southern Utah's landscape well.

Best for: Rustic aesthetics, walls under 3 feet, properties where a natural look matters more than clean lines.

Typical cost: $15-$25 per square foot depending on stone source and availability.

Poured Concrete Walls

Poured concrete retaining walls are the strongest option but require the most equipment and skill. They need forms, rebar, proper concrete mixing, and curing time. Most homeowners hire this out unless they have concrete experience.

Best for: Walls over 4 feet, structural applications, locations with heavy surcharge loads (driveways, parking areas above the wall).

Typical cost: $20-$35 per square foot for materials, plus significant equipment rental.

Equipment You'll Need

The right equipment makes the difference between a weekend project and a week-long ordeal. Here is what you need and why each piece matters.

Mini Excavator (For Walls Over 3 Feet)

A mini excavator handles the base trench excavation dramatically faster than hand digging. For walls over 3 feet, you are moving serious volume --- a 20-foot-long wall at 4 feet tall requires excavating a trench roughly 24 inches wide and 12-18 inches deep, plus the area behind the wall for drainage gravel. That is several cubic yards of material.

Recommended: Bobcat E20 or E35 from BeeHive Rental. The E20 fits through standard backyard gates; the E35 handles harder soil and deeper cuts.

Plate Compactor

This is the single most important piece of equipment for retaining wall construction. You will compact the base gravel before the first course, then compact the backfill gravel behind every subsequent course. Skipping compaction is the fastest path to wall failure.

Recommended: A standard forward-plate compactor handles most residential retaining wall projects.

Concrete Saw

If your layout requires cutting blocks to fit corners, curves, or end caps, a concrete saw with a diamond blade makes clean, precise cuts. Trying to split blocks with a hammer and chisel works in a pinch but produces rough, uneven cuts that show in the finished wall.

Recommended: A 14-inch cut-off saw handles all standard retaining wall block sizes.

Wheelbarrow and Hand Tools

You will move a surprising amount of gravel during a retaining wall project. A sturdy wheelbarrow, a 4-foot level, a rubber mallet, a shovel, a rake, and a string line are all essential. A hand tamper is useful for tight spots where the plate compactor cannot reach.

Materials List

For a standard segmental block retaining wall, gather these materials before you start:

• •Retaining wall blocks --- Calculate square footage of wall face, then check the manufacturer's coverage rate per block
• •Wall caps --- One cap per block on the top course
• •Construction adhesive --- For securing caps and any cut blocks
• •Gravel base material (3/4-inch crushed stone) --- For the footing trench, 6 inches deep minimum
• •Drainage gravel (3/4-inch clean stone) --- For backfill behind the wall, 12 inches wide minimum per course
• •Perforated drain pipe (4-inch) --- Runs along the base behind the first course
• •Landscape fabric --- Wraps around the drainage gravel to prevent soil infiltration
• •Backfill soil --- For the area behind the drainage gravel zone

Step-by-Step: Building Your Retaining Wall

Step 1: Layout and Planning

Mark your wall location with stakes and a string line. Use spray paint to outline the excavation area, which extends 12-18 inches behind the planned wall face for drainage space.

Critical: Call 811 at least 48 hours before digging to locate underground utilities. This is free, legally required in Utah, and prevents catastrophic (and expensive) mistakes.

St. George permit note: The City of St. George requires a building permit for retaining walls over 4 feet in height in front yard setback areas. Walls that retain a surcharge (driveway, structure, or significant slope above) may require engineering regardless of height. Contact the City Building Department at (435) 627-4830 before starting walls that approach these thresholds.

Step 2: Excavate the Base Trench

Dig a trench along your entire wall line. The trench should be:

• •Width: The depth of one block plus 12 inches behind for drainage
• •Depth: 6 inches of gravel base plus enough to bury the first course of block at least halfway below grade (for a typical 6-inch-tall block, that means 9 inches total depth minimum)

For walls over 3 feet tall, use a mini excavator for this step. Hand digging a 20-plus-foot trench to the required depth is backbreaking work, especially in Southern Utah soil.

Southern Utah specific: You will likely hit caliche --- a calcium carbonate layer ceite that is common in desert soils around St. George. Caliche can sit anywhere from 6 to 18 inches below the surface. If your trench hits a hard caliche layer, you have two options: use a concrete saw or breaker to cut through it, or adjust your footing to sit on top of the caliche layer (which actually provides an excellent, stable base if it is level). Consult with the team at BeeHive Rental & Sales about the right equipment for cutting through caliche --- they deal with this question regularly.

Step 3: Level and Compact the Base

Spread 6 inches of 3/4-inch crushed gravel in the trench. Rake it level, checking with a 4-foot level every few feet.

Compact the gravel with a plate compactor, making at least 2-3 passes. The base must be flat and firm --- press your boot into it and you should not leave a print. This compacted gravel base is the foundation for your entire wall. Every inch that is off-level here becomes inches of error at the top of the wall.

Step 4: Set the First Course

The first course is the most important. Take your time.

1. •Place the first block at one end of the wall, checking level side-to-side and front-to-back
2. •Set each subsequent block tightly against the previous one
3. •Check level every 2-3 blocks and adjust by tapping with a rubber mallet
4. •Use a string line along the front face to keep the course straight

Do not rush this step. If the first course is not level and straight, every course above it will amplify the error. A 1/4-inch deviation in the first course becomes a 1-inch lean at the top of a 4-foot wall.

Step 5: Install Drainage

Behind the first course, lay perforated drain pipe (holes facing down) on top of 2 inches of clean drainage gravel. The pipe should slope at least 1/4 inch per foot toward a daylight outlet or a drainage point at the end of the wall.

Wrap the drain pipe and surrounding gravel in landscape fabric to prevent soil from clogging the perforations over time. This drainage system is what keeps water pressure from building behind your wall --- the primary cause of retaining wall failure.

Step 6: Backfill and Compact Each Course

For each course above the first:

1. •Stack the next row of blocks, offsetting joints by at least 3 inches (running bond pattern)
2. •Check level and alignment
3. •Fill behind the blocks with 12 inches of clean drainage gravel
4. •Compact the gravel with a plate compactor
5. •Backfill behind the gravel zone with native soil
6. •Compact the soil

This step repeats for every single course. Do not stack multiple courses and then backfill --- the individual-course compaction is what creates a structurally sound wall.

Step 7: Cap the Wall

Once you reach your final height:

1. •Clean the top surface of the last course
2. •Apply construction adhesive in a zigzag pattern along the top of each block
3. •Set the cap blocks, pressing firmly into the adhesive
4. •Check alignment and level
5. •Allow the adhesive to cure for 24 hours before loading the wall

Step 8: Final Grading and Cleanup

Grade the soil behind the wall to slope away from the wall face. You want surface water to flow away from the wall, not toward it. Plant groundcover or lay sod behind the wall to prevent erosion that could overwhelm your drainage system.

Critical Mistakes That Cause Wall Failure

Poor Drainage (The #1 Killer)

Water saturated soil behind a retaining wall creates hydrostatic pressure that no residential wall can withstand indefinitely. Install the perforated drain pipe. Use clean drainage gravel. Make sure the pipe has an outlet. There are no shortcuts here.

Inadequate Base Compaction

A retaining wall is only as stable as its foundation. If the base gravel is not compacted properly, the wall will settle unevenly over time, creating cracks and lean. Rent the plate compactor. Make multiple passes. Check with a level.

Skipping Course-by-Course Compaction

Backfilling behind the wall all at once instead of compacting each course leaves voids that settle over months or years, pulling the wall backward. The compaction step is tedious but non-negotiable.

Building Too Tall Without Engineering

Walls over 4 feet in most jurisdictions (including St. George for front yard setback areas) require engineering. Even if your wall does not technically require a permit, walls over 4 feet without proper geogrid reinforcement and engineered design are at high risk of failure. The soil pressure increases exponentially with wall height.

Southern Utah Considerations

Caliche sub-layers: As mentioned above, St. George area soils commonly contain caliche layers that affect excavation depth. Plan for extra equipment rental time if you hit this layer.

Extreme heat: Schedule your wall project for early morning work during summer months. Southern Utah temperatures regularly exceed 100 degrees by midday from June through September. Block adhesive, your body, and your equipment all perform better in morning temperatures. Start at first light and plan to be finished by noon.

Soil composition: The red desert soil in the St. George area drains better than clay soils in other regions, but it still requires the full drainage system behind your wall. Do not assume that desert soil means you can skip drainage --- monsoon season brings intense, concentrated rainfall that saturates the ground quickly.

Cost Comparison: DIY vs. Hiring Out

The savings are significant. A 20-foot-long, 4-foot-tall retaining wall (80 square feet of face area) costs roughly $1,200-$2,000 in materials. Add $200-$500 in equipment rental from BeeHive Rental and your total lands between $1,400 and $2,500. The same wall professionally installed runs $2,000-$4,000 or more.

FAQ

How deep should a retaining wall footing be?

The base trench for a retaining wall should be deep enough to accommodate 6 inches of compacted gravel plus half the height of the first block course buried below grade. For a typical block wall, this means 9-12 inches of total trench depth. In Southern Utah, if you encounter a level caliche layer at your excavation depth, it can serve as an excellent footing surface.

Do I need a permit to build a retaining wall in St. George, Utah?

In St. George, retaining walls over 4 feet in height within the front yard setback area require a building permit. Walls that support a surcharge load (driveway, structure, or steep slope above) may require engineering regardless of height. Contact the St. George Building Department at (435) 627-4830 for project-specific guidance before you start.

What causes retaining walls to fail?

The number one cause of retaining wall failure is inadequate drainage. When water cannot escape from behind the wall, hydrostatic pressure builds and pushes the wall outward. Other common causes include insufficient base compaction, building too tall without geogrid reinforcement, and skipping course-by-course backfill compaction.

Can I build a retaining wall without a plate compactor?

Technically you can use a hand tamper, but it is not recommended for walls over 2 feet tall. A plate compactor delivers consistent, measurable compaction force that a hand tamper simply cannot replicate across a large base area and multiple courses of backfill. Plate compactor rental from BeeHive Rental & Sales is affordable and makes a dramatic difference in the finished wall's stability.

How long does it take to build a retaining wall?

A 20-foot-long, 3-foot-tall segmental block wall typically takes a capable DIYer one full weekend --- one day for excavation, base prep, and the first few courses; the second day for remaining courses, capping, and backfill grading. Larger or taller walls may require additional days. Renting a mini excavator for base excavation saves significant time compared to hand digging.

Ready to build your retaining wall? BeeHive Rental & Sales in St. George carries plate compactors, mini excavators, concrete saws, and every other tool you need for a successful retaining wall project. The team has helped hundreds of Southern Utah homeowners and contractors tackle retaining wall builds with the right equipment and honest advice. Call (435) 628-6663 for availability and rates, or browse the full equipment inventory to plan your project.