Placement and Finishing
Preparing and Pouring
You should plan your concrete installation very carefully. Consider the weather first, then the time of year and finally your concrete provider's ability to get the concrete to you on time.
Delays after the concrete arrives create problems in finishing and can reduce final quality. Complete the excavation, compaction, form work and other preliminary steps ahead of time.
Dig out the site where you are pouring concrete. Make sure your prep area has good drainage. Remove all organic material. Make sure the soil is well packed and will not shift or settle. You do not have to bring in extra material (sand or gravel) if you properly prepare the existing dirt.
Make sure that your forms are cleanly placed and that no material rests on the bottom edge of the forms. Make sure there is an evenly packed surface for the concrete to rest in.
Before the concrete arrives, install pre-molded joint material wherever flatwork comes against buildings, steps, walls, existing slabs, and other fixed objects to avoid bonding to the structure. Joint material must extend all the way to the bottom of the slab.
If required, make sure that you have properly placed your rebar or wire mesh.
Moisten the prep site right before the concrete arrives. Do not flood the area and do not use any sort of vapor lock system.
As far as thickness goes, if you are pouring a residential driveway, a four-inch depth is fine. If you plan to drive heavier trucks, pour a six-inch pad. For extremely heavy use, pour at least eight inches.
Chute, wheelbarrow or shovel concrete directly to its final position. Don't dump it in piles and then flow, drag or rake it the rest of the way. Start at the far end and work to the near end. On a slope, use stiffer concrete and work down the slope. Spread the concrete using a short-handled, square-ended shovel, a concrete rake, or a come-along. Do not use a garden rake since it will cause segregation. Tamp the concrete with a spade or 2x4 along the edges of the form to release air voids and consolidate the concrete. All concrete should be placed as soon as possible after the mixer truck is loaded. Shorten this time in hot weather or add an admixture to lengthen the time you must place and finish the concrete. Protect any placed concrete from the hot sun, high winds or freezing temperatures.
Use a lumber or metal straightedge (called a screed) to strike off the concrete and level it. Rest the screed on edge on the top of the forms, tilt it forward and draw it across the concrete with a sawing motion. Keep a little concrete in front of the screed to fill in any low spots. Use the screed on the concrete twice.
Float the concrete as soon as it has been struck-off. A float is a wood or metal tool used to further level the concrete surface and to embed the large aggregate. On small jobs, a float is hand-held; on larger jobs a long-handled bull float may be used. One or two passes should be enough to smooth and level the surface without sealing the concrete. Floating must end before visible bleed water (water sheen) rises to the surface.
Wait for the concrete to stop bleeding. Bleeding occurs as the solids in the concrete settle and water settles on the surface. Immediately after all the bleed water is gone (1) broom OR float the surface once; (2) if hand tooled, cut control joints while the concrete is still plastic, and (3) edge. Edge the concrete all the way around. Spade the concrete next to the form gently with a small mason's trowel and use the edging tool to give the concrete rounded edges.
For the final finish, use a broom, particularly on driveways and sidewalks, as this is the safest and most durable finish. Where a smooth finish is desired, such as on a garage floor, use a wooden hand-float finish. Do NOT machine float or use a hand trowel. Never use a steel trowel on concrete exposed to the weather. Never sprinkle water or cement on concrete while finishing it.
Do not overwork or over finish the surface of any exposed concrete slab. Not only is it time consuming, but it also tends to bring too much fine material to the surface and weaken it.
Cure using desired method.
Owners and tradesmen should not drive on new, cured concrete for at least seven to ten days.
Owners should not use salt during the first winter, especially if the concrete was placed after September 15th and not sealed. Use sand instead. Do not allow snow and ice to accumulate on the slab during the first year. Never use any deicer that contains either ammonium sulphate or ammonium nitrate. Be aware that salt can accumulate on your car and fall onto the driveway.
Be sure to regularly seal the finished concrete in order to protect and prolong its life.