If you are building on a level area, the monolithic slab is a good alternative to the traditional footing and block. The monolithic slab originated in areas where the soil conditions were not good. The concept is for the footing and slab to function as one unit and if settling or movement occurs, the whole will move rather just a portion. There is some truth to this.

From a cost and time standpoint, the monolithic slab is a good way to go. Because you don’t need a block mason, you have one less contractor to bother with.

Usually the footings for a monolithic slab are narrower than for the conventional. Some designs call for a 12” wide footing. If the pad is graded level, most footings only measure 20- 24” from the top of the slab to the bottom of the ditch. Your building plans should specify this.

Monolithic slabs require carpentry skills to build forms and set them to grade. Some of the concrete subcontractors are highly capable of doing this work, but it is usually best to get carpenters involved. If you plan to do the work yourself, that is why I wrote this article. If you are setting forms yourself, it is much easier to do it with at least one person to help. I have set them on my own, but it is difficult and slow.

If you are bricking the outside of your building, a form has to be built to allow the concrete to go under and past the line of the exterior wall for a footing for the brick. The usual way to do this is to make a form that is at least 8” high and 5” wide. It is best to build with the brick ledge added, even if you have no intentions of bricking the building. It is much harder to add a footing at a later time, should you decide to add brick veneer later.

If you want to forgo the brick ledge, the forms can consist of 2″ x 8″s or 2″ x 10″s. This saves about a cubic yard of concrete for every 54 feet of exterior wall.

NOW, let me tell you how I prefer to do it.

If the building will have masonry veneer, or if there is a chance it might have sometime in the future, dig the footings 16” to 18” wide. The person digging the footing should center the ditch under the string that is for the building line. The reason for the ditch being wider than the plans may call for is two fold. First, when the forms are set in place, it is much easier to put the rebar in the ditches. Secondly, there is more room for error if the ditch isn’t completely accurate. If you are not putting the brick ledge in, typical designs call for a 12″ wide footing. Digging the footer wider just gives you more room to work when driving stakes.

Build the forms to be 12” high. Using 2 – 2” x 6” with 9” long blocks between them. Then, put 7/16” OSB on one side that will face the interior of the slab. If the forms are made 8’ long, they are easy to handle and set in place. Blocks at each end and one in the middle are sufficient to hold the concrete. Some people prefer the forms to be only 8” high. I prefer 12” because that generally ensures that your brick will start below finished grade, and the concrete beneath will not be seen. You will need enough forms to completely go around your slab.

With ditches dug and building lines pulled, you are ready to set forms. Before you do that, let’s consider a few things. The best way to make sure that forms do not touch building line strings and cause them to be inaccurate is to gauge the forms below the strings. A small piece of ½” plywood works well for the gauge, as it can be dropped in your tool apron and retrieved each time you are ready to nail your stake to the form.

Your building strings should be to the outside of your exterior walls, so the forms will line up with the strings and be set to the outside of the building. It will take three stakes to hold up a form. If you are building on firm ground, an 8’ 2” x 4” will yield 3 stakes 32” long. Cut sharp points on one end of each.
Your stakes should be located strategically so that the two on the ends will measure 8’ from center to center. This is done so that the next form that abuts can be nailed to the same stake. Turn the 3½” side of the stake parallel to the string line. Measure 6½” from the string line to the outside of the building and drive the stake plumb into the ground. (Please, don’t call it level. Level is horizontal. Plumb is vertical.) Be sure not to drive the stake below the top of your form.

Next time we will look at setting the forms.

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