How to Build a Stem Wall
Building a concrete stem wall can be done with block, rod, and concrete without the use of any mortar. Dry-stacking the blocks is easier than using a mortar and gives you more flexibility. Essentially, the blocks act as a formwork for the wall and the voids can later be filled with rebar and concrete in small batches. A stem wall can be erected and when everything is straight and level, it can be locked in place with concrete infill. With the right tools and direction, you will find it very easy to build a stem wall.
Step 1 - Prepare the Site
Set up the batter boards at the corners and run the masonry lines between them along the perimeter of your wall. Attach the lines to the cross member and when they are where you need them, hammer a nail in and wrap the masonry line around it to hold it in place. The masonry lines will be used as guides. The outside of the wall will be flush with the lines
Step 2 - Lay the Bottom Row of Blocks
You may now begin to lay your blocks at the lowest elevation of your foundation. Run the bottom row of blocks until they go completely below the grade. If your foundation is a stone or gravel mix, ensure that the foundation is tamped well. Wetting the foundation can help. Use the rubber mallet to pound the blocks into position. The bottom row is the hardest part of constructing the wall. However, each row above it will be relatively easy.
Step 3 - Gravel
Backfill the bottom row of your wall with gravel on the inside and outside. This procedure will help in planting the wall and keep it dry. Also, the gravel will keep out any growth and roots away from the wall structure.
Step 4 - Rebar
Cut the 3/8 inch rod for your wall with the bolt cutters 12 inches longer than the height of your wall. You want the rod to be this long so that you can pound it down through your foundation. You will need a rod for every void in the block. This will give you excellent stability for your wall.
Step 5 - Mix Concrete
Mix your concrete per the instructions on the bag for the proper consistency. You want your concrete to be a heavy wet batter.
Step 6 - Place Concrete into Voids
Take your concrete mixture and scoop it into the voids of the wall. The concrete should be chunky heaps as you fill the spaces and not runny. Pack the concrete in with your spade and then smooth the top of it off with the trowel.
Step 7 - Insert the J-Bolts
You will want to use the longest bolts that you can find and ensure that they extend 3 inches above the stem wall to make room for your sill plate and the washer and nut that goes on above it. Pack concrete around the bolt and smooth around it with your trowel.
Step 8 - Curing
Allow the concrete to cure so that the moisture in the cement is fully absorbed. On hot days, spray the fixture at least once during the day. The longer it takes to dry, the stronger the structure.
Step 9 - Finish the Wall
Once the curing process is done, continue around the perimeter of the foundation until you meet at the end of completion. If you have a helper or two, it is better to operate in two directions from one point and meet at the opposite corner. This will prevent going too high or too low at any point in your wall.