How to Pour Concrete

Only pour concrete at a well-prepared job site with a drained and compacted base of soil to start on. Acquire all necessary permits and determine the location of any underground plumbing or wiring. Additionally, prepare all materials for building the concrete forms.

A 4- to 6-inch compact base is common. However, load-bearing slabs such as driveways may require 10- to 12-inch bases. This is also true of cold climates or places with heavy clay soil. Ensure the soil is well drained to prevent the concrete from cracking when the earth expands and contracts.

Once the base is drained and compacted, prepare the location for pouring concrete with the following steps:

• Determine the location of the concrete slab. Measure and record the lengths of the sides and place stakes at each corner. Ensure the angles are correct and adjust as needed.
• Run string lines from the stakes at each corner to create an outline of the site. If the ground slopes, flatten the area as needed.
• Choose the materials and build the concrete forms on the determined site.
• Spread 3-4 inches of gravel aggregate within the formwork. A base of gravel will help prevent erosion and keep the slab from settling.
• Pour concrete sand to fill the gaps in the gravel base.
• Use a tamper or plate compactor to flatten the gravel base. If needed, add more gravel and compact until you have a 4-inch base.

For other steps to make concrete slabs, see our guide on How to Build Basic Concrete Forms.

After placing the concrete forms and compacting the base, install steel reinforcement if needed. Reinforcing concrete with rebar or wire mesh makes the slab stronger and helps prevent cracks. Some permits or building ordinances require steel reinforcement, so check the requirements in your area.

Steel reinforcement may not be necessary for residential walkways, shed floors or other slabs that will hold less weight. Reinforcement for concrete patios are optional, but will be necessary to support a hot tub or other large amenities. Carports, garages and driveways should be reinforced even when it is not required.

Place steel reinforcement in the upper third of the slab. Steel reinforcement at the bottom of the slab will not protect against the shrinkage and temperature cracks at the surface.

Concrete slabs less than 5 inches deep can benefit from wire mesh reinforcement. Follow these steps to install wire mesh:

• Purchase wire mesh in flat sheets not rolls.
• Measure the concrete slab’s length and width. Subtract 2 inches from each side. Cut the wire mesh to fit this measurement and ensure that the mesh is not exposed at the edges of the slab.
• Raise the wire mesh with support structures, such as concrete blocks about 3 square inches. Cut the blocks to about half of the slab’s height and place them about 3 feet apart throughout. Properly sized metal or plastic support chairs are good substitutes for concrete blocks.
• Place the mesh on top of the supports. If the slab’s width requires multiple mesh sheets, make sure they’re large enough to overlap one foot along the edges.
• Fasten the wire mesh sheets using steel ties.

Concrete slabs of more than 5 inches in depth should have rebar reinforcement, which offers greater structural integrity for higher load-bearing surfaces. Follow these steps to install rebar in a concrete slab:

• Purchase the required lengths of 1/2-inch rebar. Cut the rebar on-site or purchase pre-cut lengths. If needed, purchase corner bars or use a rebar bender to bend lengths of rebar for the corners.
• Position the support structure.
• Lay the lengths of rebar in the formwork to create a two-foot grid pattern.
• Use a tie-wire twister to attach the rebar with precut rebar ties.

Pro Tip: Lay the wire mesh or rebar in the formwork to make sure it fits properly and that no metal will be exposed after pouring the concrete. Then remove the metal reinforcement, place the supports and position the metal reinforcement on top of them.

Once you’ve prepared the base, concrete forms and metal reinforcement, you’re ready to pour the concrete. Prepare your concrete mix, pour it into the framework and make sure it fills the concrete form completely. Follow these steps for pouring mixed concrete into your form:

• Use a garden hose to soak the base with water before mixing the concrete. A damp base helps prevent fresh concrete from drying or curing too quickly.
• Place plastic sheeting around the formwork in case any wet concrete spills.
• Mix concrete according to instructions.
• When the concrete mix has the consistency of peanut butter, pour it into the form. Pour the concrete as close to the center of the formwork as possible.
• Depending on the size and placement of the site, you may be able to pour the concrete directly from a concrete mixer’s chute, or you may have to transfer the concrete using wheelbarrows and shovels.
• If the concrete slab has steel reinforcement, make sure concrete completely covers the wire mesh or rebar. This supports the mesh and helps keep it from sinking.
• Use a mortar hoe to ensure the concrete is evenly distributed throughout all corners of the form. Make sure the fresh concrete is level with the top of the formwork.

Pro Tip: If you spill outside the concrete form, wait for it to dry and then scrape it up.

Once the concrete has been poured into the formwork, you must level and finish it as quickly as possible before it sets. Use a concrete screed or a long wooden board following these steps to flatten the surface of the wet concrete:

• Lay the screed or board on top of the form and pull it back and forth across the surface to even out lumps and remove excess concrete. Repeat until the surface is level. If the slab is on a slope, start from the most uphill point and work down.
• Further smooth the surface immediately after screeding. For smaller slabs, use a hand tool such as a darby. For larger slabs, use a long-handled concrete float. Sweep the tool in smooth arcs to level the surface. Expect this to force down the larger pieces of aggregate and cause moisture to pool at the top.
• If needed, complete the finishing process by using a concrete trowel or hand float. Do not overwork the concrete.
• For larger slabs, cut control joints into the surface to accommodate shrinkage and changes in temperature. Use a groover to cut grooves about 25% into the depth of the concrete. Space the joints no more than 2-3 times (in feet) of the slab’s thickness (in inches). For example, a 4-inch slab should have joints no more than 8-12 feet apart.
• Remove the formwork and cure the concrete as described in When to Remove Concrete Forms.

When finishing a concrete patio or driveway, using a broom can ensure the surface will not be too slippery after drying. After floating the concrete, lightly run a concrete boom over the surface. If the surface slopes, run the broom-strokes perpendicular to the slope. Broom finishes are as durable as other types of finish but may not be as decorative.

Not every concrete pouring job is the same, and factors like preparation, weather, safety and tools will impact your work process. For example, wet and rainy climates could affect scheduling due to drying and curing concerns. Remember these tips during concrete slab preparation, pouring and finishing:

• When possible, pour concrete in warm, dry weather. A temperature of 70 degrees Fahrenheit or more for five days after pouring provides better conditions for curing.
• Wear work gloves, safety glasses and long sleeves when mixing and pouring concrete. Do not let wet concrete touch exposed skin. Wear a face mask when using dry concrete mix.
• A gravel base may not be needed in frost-free climates.
• When preparing the site, dig a trench along the inside of the framework an additional 3-4 inches deep and 5-6 inches wide. This will help anchor the concrete slab to the ground.
• Screed boards with a slight bow or crown in the upward-facing side can help drain the water in the concrete. If the bow or crown faces down, it may create a trough where the water will pool.
• Clean every tool as soon as you finish using it to prevent concrete from drying on it.

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