How To: Pour Concrete
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Pouring concrete yourself may save you money and build your skills, but without proper equipment and attention to detail, the results can look far from professional. Concrete—generally a combo of cement, sand, gravel, and water—is tricky to mix and manipulate. Moreover, it’s fairly quick drying constitution tends to make any mess-ups permanent. Fortunately, whether you plan to make patio slabs or driveways, working in small areas divided by concrete forms following this guide on how to pour concrete makes this daunting material more manageable.
Before you begin, expect to use just more than seven bags of concrete for every cubic-meter of concrete in your project. And keep in mind that while concrete can be poured nearly year-round, except in freezing conditions, you’d be wise to put off doing it in very hot weather. At temps above 90 degrees Fahrenheit, concrete can “flash set,” and while preparing the mix at a higher water-to-mix ratio can prevent this, it can also weaken the concrete, making it more likely to crack or a flake over time. For an ideal pour, work in temperatures around 60 degrees Fahrenheit or in early morning hours to outsmart summertime heat.
MATERIALS AND TOOLS Available on Amazon
– Measuring tape
– Squarepoint shovel
– Gravel for subbase
– Hand tamper
– 1×4 boards
– Concrete mix
– Filtered water (optional)
– Long 1×4 or other board to use as a screed
– Wood float
– Magnesium float
– Finishing broom
– Plastic mixing tub, concrete mixer, or wheelbarrow
– Gallon measuring pail
– Work gloves
– Safety glasses
– Concrete sealer
Measure and prepare the area where you plan to pour concrete. If this involves digging up earth to prepare a subbase, first ensure there are no gas lines or buried cables below the surface. Contact power, gas, or city authorities if your home’s blueprints don’t show where buried lines and cables are located. Remove all sticks, twigs, odd-sized stones, and other obstructions that could cause air pockets or an uneven concrete surface. Then use a 48- to 72-inch-long level to ensure the ground is perfectly flat. If not, do some grading by moving soil around with the shovel and test with the level again.
Compact the subgrade—the earth or soil that will lie beneath a subbase layer of gravel—by compressing with a hand tamper. This flat-bottomed plate with a broom-length upright handle allows you to apply weight by pressing down or standing atop it. Work the hand tamper evenly over the entire area to create a firm subgrade, which will prevent the concrete from cracking down the line.
Put a 4- to 8-inch layer of subbase gravel or stones over the compacted subgrade. Open-grade stones are cheaper and allow more water drainage, but finer-grade stone or gravel compacts better and can sometimes ensure a more stable end product. Use the hand tamper to compact the gravel over the subbase.
Build a form around the perimeter of the subbase out of 1×4 boards and nails, into which you’ll directly pour concrete mix. Use the level to ensure the form is of even height, which will help ensure level concrete in the finishing stages. If you’ll be using this concrete project for heavy load-bearing, like a driveway or a base for a work shed, it might be wise to use rebar or wire mesh to help reinforce it.
Don your goggles and gloves to prepare for mixing the concrete. You can rent a concrete mixer for about $85 a day, but a wheelbarrow, shovel, and elbow grease will suffice. If you have hard water in your region, mix with filtered water to avoid the whitish look of efflorescence blooming on the concrete. (For detailed info on mixing concrete, including how much you’ll need and proper consistency, go here.) Keep a five-gallon bucket of water or garden hose nearby to use for cleaning tools and the mixing vessel in order to prevent concrete from setting.
Tilt your wheelbarrow of mixed concrete into the form to pour the contents. If you’ve enlisted friends to help, get all hands on deck and scrape the concrete into the form as quickly as possible. Be sure to pour enough concrete to fill up to the top of the form boards, which will make finishing the concrete easier. Rinse the wheelbarrow as soon as it’s empty to keep residue from hardening.
Quickly “screed” the poured concrete before it begins to set with a clean, long plank of wood, like a 1×4 or 2×4. Ideally, rest the narrow side of the screed board over the top of the form boards on either side of the perimeter, with the screed board in contact with the concrete surface. Now jig it back and forth slightly as you hand-drag it from one end of the concrete project to the other to smooth and level out the concrete. Repeat this step as needed till you achieve a smooth surface.
For a truly professional job, use both a wood or bull float and magnesium float to further smooth the concrete. First, apply the larger flat-bottomed wood or bull float to the concrete. When pushing the wood float away from you, keep the far side slightly elevated, and when bringing the float back toward you, the side facing you should be slightly elevated—this will help avoid drag marks. Use the magnesium hand float next, with sweeping semi-circular motions for the final finish.
Groove the concrete every four to six feet in width. This will let it expand and contract with temperature changes, preventing surface cracks. “Groovers” can be long-handled tools for working while standing and reaching, or hand tools for crouching close-up work. Both work the same way, cutting a groove through the depth of the concrete. A long-handled groover will make it easier to cross a wider project with a straighter line.
For an edge against slippage in wet conditions, “brush” the concrete by dragging a broom over the surface. Allow concrete to set just enough so that brushing won’t cause clumps. (How long to wait will depend on the temperature and humidity you’re working in.) If clumping occurs, smooth the section again with the magnesium float and give it a little more time. Once the concrete’s no longer clumping on the broom, do light dragging patterns across the entire area. Be careful that the brushed pattern’s grooves aren’t so deep that water can pool in them, as this can cause surface flaking over time. Once the whole surface is grooved, you’ll have created safe non-slip traction.
Now seal the concrete with a concrete sealer recommended by your local home center. Once you’ve applied the sealant, take measures to protect the concrete by roping it off, so it can safely cure for the industry-recommended 28 days. Feel free to walk on concrete after three days, as that won’t create scuff marks or gouges, but it’s recommended not to drive or park on concrete for at least seven days. For heavy equipment (like a concrete truck, for example), it’s best to wait the full 28 days.
To keep concrete looking great for decades, periodically wash it down with soapy water and rinse. Re-sealing every five years will further protect it.