How to Build a Cinder Block Retaining Wall

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© 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. This Retaining Wall is actually built with Concrete Blocks "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 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
  • Cement trowels
  • Hacksaw or grinder to cut steel rebar
  • Shovel, Picks, hammer, sledge hammer
  •   Pickets for staking footing forms
  • Dimensioned lumber to build footing forms  (2x6, 2x8 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!
A very old concrete block retaining wall  Note the cap.

An elegant historical  retaining wall built with concrete  block rubble

Concrete Rubble block Retaining Wall    Note the cap

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. 12. Install a perforated weeping tile or pipe on a layer of crushed rock at the base of the footing on the uphill side.  Install the pipe with the drainage holes facing down. Cover the pipe with crushed rock or very coarse, free-draining gravel. Ensure the ends of the pipe direct any water away from the wall. Camouflage the ends of the pipe as desired. 13. Back fill the first two courses adjacent to the wall with free-draining gravel and pack with a plate packer if available to minimize future settling. 14. Install all subsequent courses, filling ALL courses with cement and installing additional reinforcing bar and deadmen supports as required. 15. Install facing flagstone, brick, or alternatively apply mortar to the face (as stucco) if desired to finish the visible wall face as chosen. 16. Cap the final course as desired and complete the back filling. Compact the fill and install topsoil, and seed or sod and landscape. Your cinder block wall, as any other masonry structure, if carefully built upon a solid foundation adequately constructed, will provide many years of service.   You're free!  On to the next project!

**

Is that Incoming I hear?   ©  Photos by R.A.Kukkee +facebooktwittergoogle_plusredditpinterestlinkedinmailfacebooktwittergoogle_plusredditpinterestlinkedinmail

12 thoughts on “How to Build a Cinder Block Retaining Wall

  1. I live in Florida, and I’m planning to build a cinder block retaining wall to level my back yard. It shouldn’t be higher than about 5ft. My yard currently slopes right into my rear neighbor’s backyard so I want to make sure the wall is solid and doesn’t crumble to pieces into his backyard the first time a large storm comes through. Your instructions seem very thorough, but can you provide diagrams for the construction by any chance? Thanks for you site!

    • Hi Mike,
      Because soil and moisture/slump conditions are seldom the same on slopes and hillsides at different locations, it is impossible to recommend a specific size of footing, etc. to you,– but I will forward a generic diagram to you in the next day or so. As a DIY’er, if the soil is known to be unstable in that area, you may wish to consider two parallel walls across the slope, but lower in height to achieve the stability you need–and have a nice step lawn area in between them which can be very attractive for special purposes. Good luck with your landscaping project! ~R

  2. Mike, I live in central Missouri. The frost line here is 20,” so I will trench a footing a little deeper than that. My retaining wall is on a slope and will start at about 18″ and finish pretty close to 6′ high. It runs the entire length of my driveway and there is currently a railroad tie wall that is falling down. Should I have a footing that will have the retaining wall lean towards the higher side? Would that make it more stable and resist the weight of the earth pushing back more effectively?

    Thank you.

    Dan

    • Dan, if the existing RR tie wall is collapsing, especially leaning out, that’s a pretty fair indication the soil is unstable, creeping or slumping. Are the conditions very wet? It may be failing because of inadequate drainage, which can be a tremendously important factor.
      Your retaining wall on one end is going to be close to 6′ high, it is a good idea to have it ‘lean’ into the hill to some degree. That will help, but perhaps not solve the problem if the soil in that area is known to be constantly slumping, friable and unstable –that can be a real issue and a challenge. If very unstable,– for a block retaining wall, restraint is needed, certainly add galvanized deadmen cable anchors in the sections higher than 3′, and add them every second course of block i.e. course 3 and course 5;. Install them every 8′ of length, and tie them into the block courses.
      Alternatively, weight of the hillside itself can be used to counter slumping soil; consider adding a geogrid reinforcement mesh at about the 3′ level, on the higher section, running the geogrid mesh uphill, and loading it with excavated fill –tie it securely with mortar into the block course. (See “How to build a Geogrid reinforced retaining wall) If conditions are really unstable, or if there is a lot of soil vibration from passing traffic, you may even wish to consult an engineering firm. Best luck with your project! ~R

      • Raymond,

        Thank you so much for your reply. The RR tie wall is not leaning out, and I see no real signs that the earth is unstable. They’ve simply been there for 30 years and they are rotting away. However, soil here is very charged with clay so it does expand and shrink as moisture content varies. I will definitely use the geogrid and anchors as you suggest. Do you think it should also lean? If so, how much?

        Thank you.

  3. @ Dan, if the old retaining wall isn’t broken, leaning out or showing sign of stress other than decay and old age, the slope is likely relatively stable and hasn’t been slumping, so the extra expense of a geogrid mesh probably is not necessary.
    On the high section, do install deadman anchors, and with an appropriate footing below frost level, very minor lean-in, perhaps an inch. With a clay component you have described the expansion/contraction of clay is the dominant problem; it is absolutely essential to get the footing reinforced and the drainage right–and perhaps even more importantly, backfill the wall with free-draining gravel on the uphill side of the wall to avoid any moisture, frost/freezing/expansion of clay against the block wall. The expansion of clay is a powerful force, keep it away from the structure.

    • Raymond,

      I’m sorry for all of you follow up questions. But I’ve been doing some research into the deadman anchors. All I find on the internet are anchors that are used for timber walls. Therefore, they are made out of wood. How do I make an anchor for a cinder (or concrete) block wall? Is this something I’m going to have to purchase? If so, where?

      Also, you said that if I do make the wall lean, I should only make it lean by about one inch. My concern is that it will look like I just didn’t make the wall straight. Would it not be better to get a definite lean, like they do with retaining wall block systems that have a setback for each course? (Although I assume a set back on each row is probably a bad idea.)

      If I do make the wall lean, do I do that by making the top of the footing have an angle (one side of the form higher than the other?) Or do I do it by adding extra mortar under one side of the blocks on the first course?

      Thank you in advance.

      Dan

      • hi Dan, no problem. For your deadman anchors, go to an industrial supply house, ideally you should be able to find some galvanized steel cable type anchors of various lengths, with a steel bracket on one end that you can notch into a course of blocks (under the next course) The alternative option is to drill blocks and install eye bolts with supporting galvanized plates on the downhill side of the wall –but again that’s not the most attractive option. You you can loop the uphill end around a galvanized screw earth anchor with a cable clincher, –or use a steel plate anchor buried vertically –or even cable-clinch the anchor to an eye-bolt through a RR tie buried n a trench parallel to the wall (-in undisturbed earth!) on the uphill side of the wall.

        About the lean, if you bother to lean the wall at all, (and it may not be necessary in your application with the stable slope ) it is neater to lean the footing instead of installing courses with a back-set…back-setting each course really isn’t very attractive unless the blocks are designed for that purpose…. A positive lean IS more attractive — You could lean that wall 4″ or more without a problem if you like that ‘look’ better. You should build something you can be proud of.
        You may also wish to consider precast, ballasted blocks, which are specially designed, dry stacking, (lock stone type) but you fill them with ballast rock or gravel. There are a LOT of options. Choose carefully, and have fun.
        –btw Dan, if you have a “building center” dealer somewhere handy that also sells precast retaining wall components, they should be able to supply you with anchors.

  4. I have almost pure sand. I would like to terrace with two, two foot walls using concrete blocks without mortar. Possible? We are on a very limited income and this is all we can afford.

  5. Hi Gwenda, if you have almost pure sand on the slope, which tends to be unstable, using 2 two-foot walls and terracing is a good choice particularly if you incorporate minimal footings. Yes, possible, if the slope isn’t too steep, concrete block without mortar can work well particularly if you use a nesting type wall block made for dry-stacking. If the slope is steeper, using ordinary concrete blocks, consider adding a strip of geogrid fabric between the courses, extended on the uphill side. The weight of the fill on the fabric behind the wall will contribute to the stability of the wall.
    Another relatively inexpensive option that may be suitable dry-stacked stone ( drystone construction) –if flat stone is available, perhaps free and plentiful locally or even from your own property.
    If you are in an area with a lot of rainfall, don’t forget drainage, make sure the sand is free-draining immediately behind the wall to prevent erosion. Best luck with your project! ~R

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