How to Build a Column Footing
A column footing is usually a block of concrete poured in the bottom of a hole so that the weight placed on the column can be distributed through a larger area. This helps prevent columns from sinking into the ground over time. Here are a few steps that will carry you through pouring your own footings.
Step 1 - Measure the Footing
Mark the spot where the exact center of the column will be. Then, measure and mark out a square that is 12 inches wider than the size of the column, and dig out the hole. A guideline for the depth is 12 inches, plus one additional inch for every three inches of column. For example, the footing for a six-inch column should be at least 14 inches deep. More is always better.
Step 2 - Level the Bottom
The bottom of the hole needs to be level. If there is not enough room to work with a shovel, use a concrete trowel. Next, measure up from the bottom 12 inches plus the depth added for column size, and stick a nail into the side of the hole at that depth on all four sides. Alternately, drive a stake into the bottom of the hole, leaving that amount of the stake exposed.
Step 3 - Calculate the Concrete You Need
Cut a piece of wire mesh the size of the hole, and set it aside. You can expect the column footing to require at least one whole bag of concrete, probably more, but the formula for a more precise calculation is L x W x H / 12, with the result being the number of bags you need, rounded up. The height is the distance from the bottom of the hole to the nails (or the top of your grade stake).
If you will be setting a column permanently, calculate concrete to fill the hole to within three inches of the top. Use a mix with small rocks in it, as these rocks will provide reinforcement and prevent cracking.
Step 4 - Pour the Footing
Mix the concrete according to your calculations. Do not mix more than needed to fill the hole up to the nails at this time. That is your actual footing and it must be poured separately first, before the permanent concrete setting can be added. Shovel or pour the concrete into the hole, but be careful not to cave in the sides. Push the wire mesh down into the concrete, approximately halfway to the bottom. The surface should be finished smooth, but not slick. Use the nails as a guide for the finish depth, with them barely above the top of the footing. However, these nails are only a guide, so use a torpedo level to make the footing as level as possible. Allow a footing to cure for at least 48 hours before setting the column.
Step 5 - Set the Columns
If you are setting permanent columns, place one end on the footing after it has cured. Brace the column so that it is held perfectly vertical when checked on all sides. Then, mix the rest of the concrete from your calculation and fill the hole to within three inches of the top.