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.

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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. BeeHive Rental & Sales in St. George rents all the equipment you need. 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
• •Walls over 3 feet require engineered equipment — a mini excavator for base excavation and a plate compactor for each course of backfill
• •Southern Utah's caliche soil layers can sit 12-18 inches below grade, requiring adjustments to your footing depth
• •DIY retaining walls cost $15-$25 per square foot of wall face versus $25-$50 per square foot for professional installation
• •Browse retaining wall equipment at BeeHive — plate compactors, mini excavators, concrete saws, and more

Understanding Retaining Wall Types

Segmental Block Walls (Most Common for DIY)

Segmental retaining wall blocks 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). Typical cost: $10-$15 per square foot for materials.

Gravity Walls (Natural Stone or Boulders)

Rely on sheer mass to resist soil pressure. Best for rustic aesthetics, walls under 3 feet. Typical cost: $15-$25 per square foot.

Poured Concrete Walls

Strongest option, requires forms, rebar, proper mixing, and curing time. Best for walls over 4 feet and structural applications. Typical cost: $20-$35 per square foot for materials.

Equipment You'll Need

Mini Excavator (For Walls Over 3 Feet)

Handles base trench excavation dramatically faster than hand digging. 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

The single most important piece of equipment. Compact the base gravel before the first course, then compact backfill gravel behind every subsequent course.

Concrete Saw

For cutting blocks to fit corners, curves, or end caps. A 14-inch cut-off saw handles all standard retaining wall block sizes.

Materials List

• •Retaining wall blocks — Calculate square footage of wall face
• •Wall caps — One cap per block on the top course
• •Construction adhesive — For securing caps and cut blocks
• •Gravel base material (3/4-inch crushed stone) — 6 inches deep minimum in footing trench
• •Drainage gravel (3/4-inch clean stone) — 12 inches wide minimum per course behind wall
• •Perforated drain pipe (4-inch) — Runs along the base behind the first course
• •Landscape fabric — Wraps around drainage gravel

Step-by-Step: Building Your Retaining Wall

Step 1: Layout and Planning

Mark your wall location with stakes and string line. Spray paint 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. The City of St. George requires a building permit for retaining walls over 4 feet in height in front yard setback areas. Contact the City Building Department at (435) 627-4830 before starting.

Step 2: Excavate the Base Trench

Dig a trench: width = one block depth plus 12 inches behind for drainage; depth = 6 inches of gravel base plus enough to bury first course at least halfway below grade.

Southern Utah specific: You will likely hit caliche. If your trench hits a hard caliche layer, either use a concrete saw or breaker to cut through it, or adjust your footing to sit on top of the caliche — which provides an excellent, stable base if it is level.

Step 3: Level and Compact the Base

Spread 6 inches of 3/4-inch crushed gravel. Rake level, compact with plate compactor (2-3 passes). Press your boot into it — you should not leave a print.

Step 4: Set the First Course

1. •Place the first block at one end, 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; adjust with rubber mallet
4. •Use string line along front face to keep course straight

Do not rush this step. 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. Wrap with landscape fabric.

Step 6: Backfill and Compact Each Course

For each course above the first:

1. •Stack next row of blocks (offset joints by at least 3 inches)
2. •Fill behind blocks with 12 inches of clean drainage gravel
3. •Compact the gravel with a plate compactor
4. •Backfill behind gravel zone with native soil
5. •Compact the soil

This repeats for every single course. Do not stack multiple courses and then backfill.

Step 7: Cap the Wall

1. •Clean the top surface of the last course
2. •Apply construction adhesive in a zigzag pattern
3. •Set cap blocks, pressing firmly into adhesive
4. •Allow adhesive to cure 24 hours before loading the wall

Critical Mistakes That Cause Wall Failure

• •Poor Drainage (#1 Killer): Hydrostatic pressure behind a wall = wall failure. Install the perforated drain pipe. No shortcuts.
• •Inadequate Base Compaction: Multiple passes with the plate compactor. Check with a level.
• •Skipping Course-by-Course Compaction: Non-negotiable. Tedious but required.
• •Building Too Tall Without Engineering: Walls over 4 feet without proper geogrid reinforcement are at high risk of failure.

Cost Comparison: DIY vs. Hiring Out

FAQ

How deep should a retaining wall footing be?

Deep enough for 6 inches of compacted gravel plus half the height of the first block course buried below grade — typically 9-12 inches total. In Southern Utah, a level caliche layer can serve as an excellent footing surface.

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

Retaining walls over 4 feet in height within the front yard setback require a building permit. Walls that support a surcharge load may require engineering regardless of height. Contact the St. George Building Department at (435) 627-4830.

What causes retaining walls to fail?

The number one cause: inadequate drainage. Hydrostatic pressure from water trapped behind the wall pushes it outward. Other causes: insufficient base compaction, building too tall without geogrid reinforcement, skipping course-by-course backfill compaction.

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 first few courses; second day for remaining courses, capping, and backfill grading.

Ready to build your retaining wall? BeeHive Rental & Sales carries plate compactors, mini excavators, concrete saws, and every other tool you need. Call (435) 628-6663 for availability and rates, or browse the full equipment inventory to plan your project.