© 2008 by Raymond Alexander Kukkee
“A retaining wall is much like a dam, and must withstand the forces of direct soil pressure”
Cinder Block Retaining Wall or Concrete Block?
For purposes of retaining wall construction, building a
© 2008 by Raymond Alexander Kukkee
“A retaining wall is much like a dam, and must withstand the forces of direct soil pressure”
Cinder Block Retaining Wall or Concrete Block?
For purposes of retaining wall construction, building a cinder block wall may be considered equivalent of building a retaining wall with ‘concrete’ block. Cinder blocks are much lighter in weight and as such may be preferred, reducing the level of hard work required. The blocks may be the same standard dimensions, and in some instances may even be used interchangeably.
Regardless, let’s go with Retaining Walls: Build a Cinder Block Retaining Wall-for homeowners and DIY’ers fortunate enough to have access to high-quality cinder blocks. The photo below shows a retaining wall built of concrete blocks simply because cinder blocks are no longer available in the author’s geographic location.
“I like cinder block better, they are lighter to work with than concrete blocks, and won’t rot like timbers do”.
“Cinder block?” Why would you want to build your retaining wall out of cinder block?” What’s the difference? Cinder block is cast using coal cinder. Concrete blocks are cast using stone aggregate and cement.
“But for a retaining wall? You want heavy block for a retaining wall, don’t you?”
When considering building a retaining wall with cinder block, that may be a reasonable and logical question. The purpose of any retaining wall is to prevent downhill or ground movement and soil erosion, so to some extent, weight is a relevant factor. A retaining wall is much like a dam, and must withstand the forces of direct soil pressure, but it must also withstand settling, and the destructive heaving and displacement caused by frost. All hollow-cavity blocks can be filled with rock or gravel ballast as the wall is constructed to provide for additional weight.
A cinder block wall properly designed can respond to all of these challenges.
Essential structural considerations include adequate design and provision for drainage, footings, stability, and mechanical reinforcement of the wall itself. Always remember that design safety criteria becomes more critical with increased height.
Here is how to build a cinder block retaining wall, keeping these critical aspects in mind.
Design the Cinder Block Retaining Wall Carefully
Make a drawing to ensure details are not overlooked.
Are you building the retaining wall in an area that has deep, severe frost penetration? If so, your footings must be deeper than the frost penetrates to provide stability through seasonal freeze/thaw cycles. Why? Wet soil expands when frozen, ‘heaving’ or raising erratically any structure sitting on it, which can damage the structure. When it subsequently thaws, the soil level subsides in a friable condition, which is unstable. Clay soils are particularly susceptible to severe freezing.
What are soil conditions like, is the ground wet continuously? Plan for control of surface water and groundwater disposal if necessary. Saturated soil is easily deformed, can slump at any time, and creeps downhill.
How high will the wall be? Structural integrity and safety issues start to become a matter concern where retaining walls are over 6′ in height. Consider building successive walls 2′ high instead, and take advantage of the usable level spaces between them for landscaping and features.
Will the wall be constructed with mortar? If so, you require a solid concrete footing. Shifting, settling and heaving will soon destroy mortar joints, at best leaving unsightly cracks requiring annual repairs.
Do you need a building permit? Do obtain any necessary permits in your jurisdiction before commencing any construction.
Locate all gas, water and electrical services prior to beginning any digging. Your local utility will gladly flag any services endangered by your construction project.
*Note: If you have to trench deeply, be sure to contact your local utilities to locate any cables, pipes, or other superstructure. Observe safety protocol and safe working practices at all times.
Tools and Supplies Required
The following common tools and supplies are essential.
Carpenter’s line and chalk line
Carpenter’s 4′ level, line level (use laser level or transit if available)
Measuring tape, hammer, wire-cutting pliers
Hacksaw or grinder to cut steel rebar
Shovel, Picks, hammer, sledge hammer
Pickets for staking footing forms
Dimensioned lumber to build footing forms (2×6, 2×8 etc. or as required)
Cinder blocks 8x8x16 or 10x8x16
Steel reinforcing bar, galvanized deadmen anchor cables
A mortar mixer rental will come in handy for larger projects.
Concrete (ready-mix delivery) and cement mortar for block-laying.
Safety: Let’s remember to use all safety protocol, necessary safety equipment, safety glasses, gloves, –make sure tools are in good condition, and most importantly, keep visitors and children clear of the work zone and moving equipment. Safety comes first!
Let’s Build a Cinder Block Retaining Wall
1. Stake out with pickets and excavate organic, soft soil from footing area to level.
If fill is required, consolidate and pack with a plate packer. If you are in a geographical zone where severe frost penetration occurs, the footing must be below the depth of frost penetration to avoid damage from freezing.
2. Install forms for the footing slab, setting the top of the forms to level.
For a typical 3′ high wall, footings should be 24″ wide and 8″ deep as a minimum. If your design specifies the wall “leans in” toward the hil