Laying concrete is one of the simplest things you can do to spruce up your curb appeal or backyard. A concrete slab can dress up your air conditioning unit, serve as a patio or driveway or even make a foundation for an outbuilding. Once you've read up on how to lay concrete, it's a relatively easy project that can be done in an afternoon. As with most do-it-yourself endeavors, patience and attention to detail will serve you well here.
Tools and Materials You'll Need
To get started, you will need a shovel, hammer, nails, a level, a wooden stake, 2-by-4 boards, rebar or crushed stone, concrete mix, a wheelbarrow and water. You can also use some optional tools for your project, such as a concrete float and plastic tarp.
Prep the Area
Determine the dimensions of your concrete slab, then dig out that area to the depth of your choice. Keep in mind that you'll be adding a foundation of crushed stone or rebar before the concrete, which may add an inch or two to the final slab height. Determine the slope of the yard and adjust the perimeter of the slab accordingly. One side may be slightly deeper or tilted to encourage water drainage away from the concrete when it rains.
Outline the area of the planned concrete slab with wooden stakes, placing them deep enough to match the combined depth of the concrete slab and its foundation.
Build a Wooden Form
Next, you'll create a form to pour the concrete into by nailing your 2-by-4 boards to the stakes in a square or rectangular fashion. You're essentially making a big frame that will hold the liquid concrete until it's dry. Some contractors use vegetable oil or other lubricants on the lumber for easier removal from the final concrete product.
Use a level to ensure boards are straight. If you're laying a concrete slab next to a house, you only need a three-sided form (the house acts as the fourth wall). For example, if you were laying a 12-by-16-foot concrete patio off of a back door, your form would consist of two 12-foot 2-by-4s and one 16-foot 2-by-4.
Add a Base to the Formwork
Create a level surface on which to add your concrete with either steel reinforcement bars (rebar) or crushed stone. The amount needed depends on the size and scope of your project. This step also helps support the concrete and prevent it from cracking, especially if you're layering on top of existing concrete.
Cover the entire surface area with crushed stone or lay rebar in a grid pattern. For example, a 12-by-16 patio would require 14 rebars: Six laid lengthwise and eight widthwise. Next, mix up the amount of concrete you'll need. You'll probably need a wheelbarrow or other large trough for this.
Before pouring the concrete, wet the ground thoroughly with a garden hose, especially if you're working with bare dirt beneath your rebar or crushed stone layer. This prevents the ground from absorbing all of the concrete's moisture, which encourages the slab to dry evenly.
Next, pour concrete into the form and spread it immediately. Take your time to compact and smooth the surface by moving a 2-by-4 board across the form or using a concrete float, which is a large flat panel that resembles a kitchen sweeper.
Let Concrete Dry
The amount of time this step takes depends on how much direct sunlight the area receives, which will speed up the process. Once it's half hardened, use an edging tool along the perimeter to create a rounded lip on the edge of the concrete.
Cut Joints Into the Slab
Cut at least one vertical line – or joint – down the middle of the concrete slab before it's completely dry. Another joint may be added but keep the spacing at least 4 feet apart. These joints allow the concrete to breathe and prevent future cracking. If cracking does occur, it's normally contained to the joints.
If you're expecting inclement weather before the concrete has properly dried, cover it with a tarp to protect it. Once the concrete hardens, remove the form and you're done.