How to Pour a Perfect Concrete Slab

A long-time pro shares some terrific tips on how to pour a concrete driveway slab that will look terrific and last for decades.

Pushing wet concrete down the shute of cement truck | Construction Pro Tips

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Pour a perfect concrete slab

A concrete driveway makes a beautiful gateway to your home that can last for decades if it’s installed correctly. But if you don’t follow the proper procedures, it could turn into a pile of rubble in half the time. The good news: Installing it the right way doesn’t take extra time or money. We tagged along with a longtime professional mason, who showed us the best ways to prevent water from pooling and stop unsightly cracking, spalling and scaling. We’ll feature the actual pour in this story. For great tips on prepping the ground before you pour a concrete slab, check out our story “Prep for Crack-Free Concrete”.

Protecting adjoining concrete with a strip of duct tape | Construction Pro Tips

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Protect adjoining concrete slabs

Our expert uses duct tape to protect adjacent concrete slabs and sidewalks. Concrete can splash when it runs from the chute onto the ground, so you’ll also want to lay plastic over doors, siding, brick, windows or anything else you want to keep clean. Smearing wet concrete into porous surfaces creates an even bigger mess, so if you do get a couple globs where you don’t want them, wait till they dry and then scrape them off.

Wetting the gravel with the hose from the cement truck | Construction Pro Tips

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Dampen the base to lengthen finish time

To extend your finish time on hot, sunny days, spray bone-dry ground with water to keep the base from sucking the water out of the concrete slab. A water spray also slows down curing, which makes for a stronger concrete slab. If there’s no hose bib nearby, you can use the water and hose that are onboard the truck. If you don’t have water on site, also use the truck hose to fill a couple buckets of water for cleaning your tools after the truck leaves.

Did you know that bags of concrete have vents? Learn more here.

Wet concrete pouring from the end of a concrete chute | Construction Pro Tips

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How to order concrete

Calculate the volume you need in cubic yards. To figure out what you need for your concrete slab, multiply the length by the width by the depth (in feet), and divide that number by 27 (the number of cubic feet in a cubic yard). Then add 10 percent to allow for spillage and slab depth variations. If you’re not sure which slump (consistency) or psi (strength) to order, ask your concrete supplier to suggest the proper mix for your slab’s intended use.

Using hand signals to communicate with the cement truck driver | Construction Pro Tips

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Hand signals for pouring a concrete slab

Here are some basic hand signals to help you communicate with the truck driver. Make sure you can see the driver’s face in the side-view mirror—if you can’t see him, he can’t see you.

Pouring concrete on to small sections of the slab | Construction Pro Tips

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Pour the concrete slab in small sections

Spread the concrete by moving the chute back and forth and by having the driver pull forward as you go. Once the truck has reached the end of a section, spread the concrete slab out evenly, and a touch higher than the form, with a concrete placer/rake. Don’t fill the whole form or giant sections because the mound of extra concrete you’ll drag back with the screed board will get too heavy.

Be prepared!

Concrete doesn’t care if you’re not organized or don’t have time to finish all the edging—it will start setting up right away regardless. Make sure all your tools are ready to go and there are at least three people on hand, one to muck and two to screed. Sometimes the truck driver will help, but don’t count on it.

Keep rebar in the center of the concrete with rebar chairs | Construction Pro Tips

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Keep rebar in the center

This rebar grid is sitting on chairs, a setup that keeps it suspended at the proper height. You won’t be able to use chairs if you have to distribute the concrete throughout the form with a wheelbarrow. If that’s the case, use the hook on the edge of the concrete placer to pull the rebar up into the center of the concrete as you pour. Rebar should be placed near the center of the slab for maximum strength, not near the ground or the surface.

Inspecting a screed board to see which side is bowed | Construction Pro Tips

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Crown side up on the screed board

A slight crown (bow) in the screed board is not only OK; it’s preferred when pouring a concrete slab. Just make sure the crown side is facing up. That will create a slight hump down the middle of the slab, so water will drain off. If the crown faces down, you’ll end up creating a trough in the slab where water can pool.

Pushing large rocks down with a bull float | Construction Pro Tips

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Push the rocks down when smoothing your concrete slab

Larger aggregate (chunks of gravel) near the surface may cause spalling (chipping). Our expert pushes the larger rocks deeper into the mix when concrete finishing. He does this by making small stabbing motions with the float on the first return pass. Start floating the slab immediately after the pour is complete. Next, learn more about the science behind concrete.

Pushing a bull float across the poured concrete | Construction Pro Tips

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Concrete finishing: start floating right away

In addition to pushing the aggregate down under the surface, a bull float helps level the concrete slab, so start floating right after you screed, while the concrete is still wet enough to shape. Whenever possible, run the bull float perpendicular to the direction you pulled the concrete with the screed board (this slab was too long to do that). That will help to smooth out the ridges, troughs and valleys created by screeding. Our expert likes to float in both directions when he can.

Cleaning tools with water from the truck | Construction Pro Tips

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Clean your tools as you go

Don’t wait till the end of the day to clean your tools. Clean them immediately after concrete finishing.

Push a fresno trowel across the surface | Construction Pro Tips

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Don’t over-trowel the concrete slab

Actually, exterior concrete surfaces don’t need to be troweled at all. But if you want to use a trowel to knock down the ridges left by the bull float when concrete finishing, make as few passes as possible and wait until all the surface “bleed water” is gone. Overworking and troweling wet concrete can trap water just under the surface, making it weak and more prone to spalling and scaling (pitting and peeling), especially on slabs poured in cold climates.

Making long strokes with an edger | Construction Pro Tips

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Make long strokes with the edger

The concrete slab should be firm before you start edging. If the edger is leaving behind large wet grooves, wait awhile before you continue. Longer strokes will result in straighter lines.

Hand float

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Keep a hand float nearby when edging

Run a hand float over the ridges left behind by the edger when concrete finishing. A hand float is also a good tool for dragging small amounts of material or moisture (cream) into any voids or dry spots near the edge.

Cutting grooves into the concrete | Construction Pro Tips

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Cut in control joints

A 100-ft. run of concrete can shrink as much as 1/2 in. as it hardens. Shrinking causes cracks. You can’t stop your slab from cracking, but you can control where it cracks. Cut in control joints to create individual sections no larger than 8 x 8 ft. for a 3-1/2-in.-thick slab, and no larger than 10 x 10 ft. for a 5-1/2-in.-thick slab. Cut the control joints at least one-fourth the depth of the concrete. You could use a groover like this one (which was necessary to match the existing slab), which works similar to an edger, but many pros prefer to cut the control joints with a diamond blade saw the day after pouring.

Pushing a broom across the poured concrete for a nice finish | Construction Pro Tips

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Create traction with a broom

A broom finish creates a nonslip surface for wet conditions. The harder the concrete, the less rough the broom will leave the surface. Try to achieve a surface rough enough for traction but not so rough that it hurts to walk on barefoot. If the broom starts to bounce as you pull, lower the angle of the handle. If possible, broom perpendicular to the direction that the slab is most visible. Wavy, crooked broom lines are less noticeable that way.

Spraying concrete sealer onto the finished surface | Construction Pro Tips

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Concrete finishing: spray on a sealer

Concrete will become significantly weaker if the water in the mix evaporates before the chemical curing process is complete. When concrete finishing, pray down the slab with water every day for at least a week to slow down the curing process. Another option is to spray on an acrylic cure and seal product. Sealing the surface also protects the concrete from scaling and spalling in cold climates. Apply the sealer right after you broom.

Sectioning off sections of finished concrete | Construction Pro Tips

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Finishing up

The slab can be walked on and the forms pulled in 24 hours. Wait at least 10 days to drive on it, and avoid spreading any ice melting chemicals for the first two years. Ask your neighbors to keep an eye on their pets before you pour, and use caution tape around the area to warn the pesky neighbor kids.

Glenn Anderson, the concrete expert

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Meet the Expert

Glenn Anderson is the owner/operator of Above Quality in Prior Lake, MN. He’s been finishing concrete slabs, laying block and stacking stone for 25 years.