© 2008  by Raymond Alexander Kukkee

"A retaining wall is much like a dam, and must withstand the forces of direct soil pressure"    

Cinder Block 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?" 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,   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. 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. , keeping these critical aspects in mind.  

 

 

The following common tools and supplies are essential.

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 hill, set the footing forms accordingly.

3. Install two rows of 1/2" steel reinforcing bar, each being 6" from the outside edge. Support the steel bar with small pieces of concrete or commercially available standoffs. The steel bar should be in the bottom 1/3 of the concrete slab, but not touching the ground.

4. Pour the concrete, ensuring the reinforcing rod is in the correct position. Fill to the top of the form. Tamp the cement and hammer the outside of the forms to avoid "honeycomb" on the outside of the slab which can weaken the slab. Finish the slab with a rough finish; screed the cement level across the form with a 2x4.

5. Optional: Establish a carpenter's line and install a row of "J" steel anchor bolts or anchors where the row of blocks will be installed. Ensure the position of the bolts will match the cavities of the blocks! Alternatively, you may wish to drill holes into the concrete later to insert vertical reinforcing bars. *Note: your design may position the wall on the outside 1/3rd of the footing to allow more soil weight on the inside of the footing for additional stability.

6. Cover the slab and allow the cement to cure for three days. Keep the slab wet for the best result. Remove the forms and proceed with building the cinder block wall.

7. Snap a chalk line to position the first row of cinder blocks.  Lay a 1/2" thick mortar bed and apply mortar to the blocks, tap the blocks into position and level as required.

8. Install vertical reinforcing bars 4' apart or less.

9. Fill the first course of blocks with concrete .

10. For the second course, alternate the joints as is standard practice in masonry for maximum strength. Install a row of reinforcing steel on top of the second course of blocks, notching out the blocks as required. Wire the horizontal steel bar to the vertical bars securely using steel wire ties. Fill the block cavities with concrete or mortar.

11. If the retaining wall is to be over 3' and the slope is steep, install deadmen anchors perpendicular to the wall every  4' as a minimum. Use galvanized deadmen cables attached to treated timbers buried parallel to the wall uphill  in undisturbed soil. Alternatively build deadmen blocks into the course or install a geogrid web between courses for additional stability.