How to Do a Cinder Block Foundation

Concrete Footing

1). Mark out the perimeter of the structure you wish to build with a measuring wheel, stakes and a hammer. Dig a corresponding trench, making it double the width of your cinder blocks and deep enough to reach your area's frost line.
2). Line the sides of the trench with plywood planks, to serve as a mold.
3). Bend steel reinforcing bars, known as rebar, into an "L" shape. Check each stem on an "L" with a level after bending, to ensure it is vertically straight. The foot of the "L" needs to be long enough to reach from one side of the trench to the middle of the trench, where the stem of the "L" will rise upwards and out of the concrete footing.
4). Walk around the trench and mark where the rebar will be placed in the concrete footing. You need one rebar for every three concrete cinder blocks in the wall, so multiply the length of your typical block by three to determine placement.
5). Mix the concrete in a tray or wheelbarrow as directed by the manufacturer and pour it into the trench, filling the trench to between two thirds and three fourths. Plant the L-shaped rebar into the locations marked in Step 4. Allow the concrete to set overnight.
6). Remove the plywood sidings after the concrete has hardened.

1). Mix a batch of mortar sufficient for 20 or 30 minutes worth of work in the same receptacle you used for the concrete, following the instructions of the manufacturer.
2). Spread a 1-inch thick layer of mortar with your trowel along the centerline of the concrete footing, with a width corresponding to the width of your cinder blocks. Extend the bed of mortar far enough to lay five or six blocks.
3). Put two lines of mortar along the outside end of your first block with your trowel. Place this into the bed of mortar and tap along the top of the block with the butt of your trowel to settle it into place.
4). Apply two lines of mortar to your next block.. Set this block so the mortared side faces down the line of the foundation, with the unmortared side set into the mortar from the previous block. Scrape away any excess mortar from the joint between the blocks with the trowel and drop it back into the wet mortar waiting to be used.
5). Continue laying block, interlacing every third block with the steel rebar pointing out of the concrete footing, until you have a complete row of cinderblocks.
6). Fill in the remainder of the trench with leftover dirt. This will bury the concrete footing and part of the cinder block foundation, leaving most of the block and rebar above the surface, upon which the wall can be erected.