DIY Concrete: How to Prepare Your Subgrade

How to prepare your subgrade

Working with exterior flatwork requires a great deal of planning, and if you’re tackling your own DIY concrete project, you need to ensure you’re fully prepared. Not only should you know how much concrete you need, but you will also want to make sure you properly prepare your subgrade. After all, if your subgrade isn’t prepared properly, it could ruin your entire concrete project. Since you don’t want the headache—or the cost—of redoing your concrete, follow these tips to properly prepare your subgrade.

Clear the area.
Before you start any concrete project, you need to be sure you have a clear area. Make sure you know the depth of your concrete project, and then remove soil, organic materials, rocks or other items in the area. Be sure to remove enough so that the final area of your concrete will sit slightly above ground.

Backfill
Unless you are pouring on virgin clay, the area will need to be backfilled with either sand, gravel or crushed stone. This will help deliver an even pour and provide strength to your concrete. Make sure that you level the backfill to a uniform depth of at least 4 inches.

Compact the subgrade.
Compacting the subgrade is very important. Depending on the size of your project, you can compact the area with either a heavy hand tamper or a vibrating compactor. The subgrade should be hard, uniform, and well drained. Failure to properly compact the subgrade will lead to cracking.

Forming
Using forms will help provide you with a clean and uniform concrete flatwork and will help determine the final grade of the concrete. It is recommended that you set your grade with a slight slope (at least 1/8-inch) so that water does not puddle on the slab. Use a string line and level to set your grade at the slab’s surface. Place stakes in the ground no more than 4 feet apart so that the face of the stake squares up with the string line. You should have a stake at every joint too.

Use the right lumber to create your forms and raise them so that the top is even and level with the string line. Once even, nail them to the stakes. Keep in mind that wet concrete can break a form, so you may want to consider bracing the form for added durability.

Once the forms are in place, your subgrade is complete and ready for the concrete pour.

Ozinga has plenty of tips and tricks for those looking to tackle concrete projects. Check out our homeowner's guide for more information on concrete projects.

Visit our Homeowner’s Guide to Concrete: The Basics