Instructions on Laying Concrete Blocks for a Foundation

Clear the inside border of the foundation hole of any debris or rocks. This is essential. In some cases, laying a thin layer of gravel to hold the first layer of blocks gives extra confidence.

Lay the cinderblocks dry first. This will give you an idea of what the finished product looks like. Always start from the corners and work outward from there.

Lay your first layer of mortar directly on top of the footings. These are the deep structures of the foundation that are normally laid by professionals. You should leave this single job to them. These are normally about twice as wide as the blocks you are using. Do not apply mortar or blocks directly on the soil. Lay a thick first coat. This will give you room to adjust your blocks later on if they are uneven.

Level the mortar until it is basically even. You can adjust the blocks on top of it later, so it need not be completely exact. Let the mortar dry for an hour or so. Do not apply blocks to mortar immediately after they have been laid. Always keep in mind that the mortar will totally dry in several hours, so do not cover an entire side with mortar, since by the time you get to the end, it will be totally dry and useless. Lay about 10 feet at a time to begin.

Place each block directly on the mortar with the empty cells sticking straight up. As you lay each block, use your level to check the blocks. Push them down with your trowel handle as necessary to make them even. Once you have a perfectly level row, use this as your guide for the rest of them. Always check with your level every 10 blocks.

Fill the open cells with concrete. At first, fill in just a foot or so. Immediately, ram the rebar straight into the wet cement. The rebar is normally about five-eights of an inch, but for larger projects, go with the half-inch bar. Then pour the rest of the cement until all the cells are totally filled. This then gives you both concrete protection and metal reinforcement. Most local codes demand this anyway for concrete block foundations.