Building Stone Steps into a Retaining Wall with Excavated Rock

[MikePhua]

Start from the Bottom and Build Up
When constructing stone steps that integrate with a retaining wall, the most stable and practical approach is to begin at the bottom. This method ensures each riser is supported by the step below, creating a structurally sound staircase that resists shifting over time. Excavators and compact equipment can assist with overdigging and setting base layers, especially when handling large slabs or irregular stone.
Terminology Note

• Riser: The vertical face of a step.
  
• Run: The horizontal depth of a step tread.
  
• Overdig: Excavating beyond the final footprint to allow for base material and compaction.
  
• 3/4 Minus: Crushed stone aggregate with particles up to ¾ inch, used for compacted base layers.
  

Stone Selection and Preparation
Using stone excavated from blasting or basement digging offers a cost-effective and environmentally conscious solution. However, consistency in size and thickness is critical. Without uniform slabs, dry-stacking becomes difficult and may lead to uneven steps. Sorting through the material to find 20 or more flat, stable pieces is essential. If natural slabs are unavailable, smaller stones can be mortared together to form risers and treads.
Recommended dimensions for comfortable steps:

• Tread depth (run): Minimum 12 inches
  
• Riser height: Between 8 and 10 inches
  
• Total rise: Calculate based on slope and desired number of steps
  

Base Construction and Compaction
Each step should be set on a compacted base of 3/4 minus stone. Begin by overdigging the footprint of the first step, compacting the base, and placing the slab. Before backfilling behind the first step, overdig the area for the second step. Continue this process up the slope, ensuring each slab is level and stable before proceeding.
Compaction tips:

• Use a plate compactor or jumping jack for base layers
  
• Backfill behind each riser with compacted aggregate
  
• Avoid using loose soil or organic material beneath steps
  

Equipment and Handling
A mini excavator with a thumb attachment dramatically improves efficiency when placing heavy slabs. The thumb allows precise control and rotation, reducing the need for manual adjustment. For smaller projects, a skid steer with forks or a loader bucket may suffice.
Mortar vs. Dry Stack
Dry stacking offers a natural aesthetic and flexibility but requires precise stone selection and placement. Mortared steps provide greater stability and allow the use of irregular stones. In high-traffic or frost-prone areas, mortar may be preferable to prevent shifting.
Field Insight and Practical Advice
In British Columbia, a consultant used basement excavation rock to build steps into a hillside retaining wall. After sorting through 300 cubic yards of material, he identified enough slab pieces to complete the project without mortar. In Missouri, a contractor built multiple stone staircases using compacted base layers and consistent slab sizes, noting that the thumb attachment on his mini excavator made the job ten times easier.
Recommendations for Long-Term Durability

• Ensure consistent rise and run to prevent tripping hazards
  
• Use geotextile fabric beneath base layers to prevent weed growth
  
• Seal stone surfaces if exposed to freeze-thaw cycles
  
• Maintain drainage around the steps to avoid water pooling
  

Conclusion
Building stone steps into a retaining wall using excavated rock is both practical and visually striking. With careful planning, proper base preparation, and the right equipment, even irregular stone can be transformed into a durable staircase. Starting from the bottom, maintaining consistent dimensions, and compacting each layer are the keys to success—whether dry-stacked or mortared. This approach blends structural integrity with natural beauty, turning surplus rock into a lasting landscape feature.