wikiHow to Build a Mortarless Concrete Stem Wall

A concrete stem wall can be built out of block, rod, and concrete, without the use of any mortar. The advantage in dry-stacking the block is ease and flexibility. The block is essentially a formwork for the wall, and the voids are later filled with rod and concrete--in such small batches it can be mixed by hand. This way a stem wall can be completely 'mocked up', and when everything is straight and plumb, it's locked in place with concrete infill. It's a very simple and solid way to build a stem wall.


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    Do the sit work. Set up batter boards at the corners and run masonry lines between them along the perimeter of the proposed wall. Batter boards are two stakes with a crossmember between them. Any scrap wood can be used. The line is attached to the crossmember, and when you've got the line right where you want it, pound a nail in and wrap the line around it to hold it in place. The lines will be used as guides; as you lay the block the outside of the wall will be flush with the line. To square up the lines, measure your diagonals (they should be equal), and/or use 3, 4, 5 triangles to make sure each corner is 90 degrees.
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    Lay the bottom row of block. Begin the wall at the lowest elevation of your foundation, and run bottom rows until they go completely below grade. If the foundation is a stone/gravel mix make sure it's tamped very well before you lay the block--wetting it can help. Use a rubber mallet to pound each block into position, both level and plumb, and against your line.
    • The bottom row is the toughest, because it's painstaking work. But every row above it is effortless - you just set the block down in a running bond. It's best if your wall is at least 2 blocks high so they interlock.
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    Backfill the bottom row with gravel both on the inside and the outside. This helps plant the wall, keeps it dry, and keeps growth and roots back away from it.
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    Cut rod for your wall. The rod can be ordered in 20' lengths along with the cement from the same place you got the block--order it all together. Go with 3/8" rod so that you can cut it by hand with bolt cutters. Depending on the steel, some 3/8" can be cut just like you'd cut a branch with a trimmer. Some can be tougher and you'll need to put your weight behind it; just lay the rod on the ground, as well as the bolt cutters, and press down with all your weight on the top handle. Cut the rod 12" longer than the height of the wall, so that you can pound it down and through your foundation. Measure and cut rod for every void in the block. This will give tremendous stability to the wall.
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    Mix your concrete. If you're making it from scratch with sand, gravel, and cement, figure out a ratio that works (typically 1 part cement to 2 1/2 sand to 3 1/2 gravel) and will fit comfortably in your wheelbarrow. Try a 5 gallon (18.9 L) bucket for proportions: 2 gallons (7.6 L) cement, 5 gallons (18.9 L) sand, and a heaping bucketful of gravel (6 to 7 gallons). Mix the sand and gravel and cement thoroughly before you add water. Stir in a liter or two of water at a time and mix well until the concrete is the right consistency--like a heavy wet batter. Mix with a mason's hoe; a garden hoe will work also. It's hard work--do it in the shade.
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    Scoop the concrete into the voids in the wall.
    It should be a chunky slop that fills all the space yet isn't runny. If it's a tad on the dry side mash it down with your spade. When a void is completely filled, smooth across the top with a trowel.
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    Insert the J bolts. Use the longest bolts you can find, and make sure they stick up at least 2 1/2", if not 3", above the stem wall, to make room for your sill plate and the washer and nut that goes on above it. If you do the math you'd think 2" would be sufficient, but if your board for the sill plate is warped you'll wish you had 3". Make sure to pack concrete down around the bolt once you've got it in straight, and smooth around it with the trowel. If any concrete gets on the threads of the bolt it can be removed with a wire brush.
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    Wet the concrete with a hose at least once a day if it's hot and dry.
    This will allow the concrete to cure properly. The longer it takes, the harder it sets. You can also cover fresh concrete with large sheets of plastic or cardboard to hold moisture in.
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    Continue around the perimeter of your foundation, until you meet at the end. It's better to move in two directions from one point, and meet at the opposite corner, than start and end at the same place. This minimizes getting off course and going too high or too low with one stretch of your wall.


  • To make this wall even stronger and more cosmetically appealing, coat it with a layer of stucco. This will provide lateral strength as a skin of plaster, with or without lath. There's even a product called 'structural stucco', which has fiberglass, and when applied is 7 times stronger than an ordinary mortared stem wall.
  • Blocks can be cut to fit with a circular saw and diamond-tipped blade ($40). If possible run water over the area you're cutting to keep down the dust.

Things You'll Need

  • Wheelbarrow
  • Hand Tamper
  • Hammer (2 lb Sledge)
  • Hoe
  • 5 gallon (18.9 L) Bucket
  • Spade
  • Trowel
  • 4' to 6' Level
  • Masonry Line
  • Bolt Cutters
  • Work Gloves
  • Torpedo Level
  • Rubber Mallet

Article Info

Categories: Landscaping and Outdoor Building