Pouring a concrete walkway provides a solid clean area to walk on. Concrete is one of the great building materials. It can be formed into almost any shape and then when it hardens it is super strong. This article teaches you how to prepare for and pour, finish and cure a concrete walkway or sidewalk.
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Keeping things safe when working with concrete is important. The acids in cement are irritating to the skin and eyes. This is a brief outline of the safety precautions you should take when working with concrete.
Concrete for large pours is measured in cubic yards. To get an exact measurement the math is as follows:
Layout The Excavation: The first step in laying out is to figure out how close the existing elevation of the ground is to the finished top of slab. This is done by placing a stake at each end of the walkway in the center of the walkway and pulling a string line between them. Set the string at the exact level of the finished top of the walkway. Now you can easily see how far down or up you need to bring the grade of the earth before pouring concrete. Remove the string but leave the stakes and start the excavation.
Excavate: If you have to dig down you need to dig down 4 inches for the concrete and at least 2 inches for gravel. The gravel provides drainage under the concrete and helps in grading under the slab to make it flat.
Use Gravel To Sub Grade: If you have to raise the sub grade it is very important that the material you build up with is compacted very well. It is impossible to guarantee that concrete will not crack but you can minimize the chances by compacting the base under the slab. The best material to work with is 3/4" gravel, it is compacted as soon as it hits the ground, as long as it is not too deep. You can use smaller gravel but larger gravel tends to have large gaps between the rocks and ends up using more concrete when you pour. Gravel is also easy to rake around and get smooth. You can use dirt along the edges of the gravel to keep it from sluffing off the sides.
Check the elevation periodically by putting the string line back up and measuring down. This is a rough grading, you will fine tune the level of the gravel after you place the forming boards and have an exact elevation.
Layout The Stakes To Hold The Forming Board: Now that the elevation is rough graded, within a few inches, drive stakes at each end of the walkway 1 1/2" away from where the finished edge will be on each side of the walkway, this is for the thickness of the 2x4 forming board. Pull a string line between the two stakes. Install stakes along the string line about every 3 to 4 feet.
Move the string line to 1 inch higher than where the top of the concrete will be, you will measure down from here to set the top of the form board.
Add The Form Boards: Cut the 2x4 boards to length and place them next to the stakes. Use nails or screws to attach the boards to the stakes. Measure down from the string to the top of the board and attach it to the stake. Move to the next stake and repeat. After you attach all the stakes to the form boards you may need to drive down or pull up a stake a bit to get the form board perfectly straight and in line with the string. (Make sure the string line is only touching the two end stakes or it will not be straight.
Set The Slope: Concrete should always have a little slope so water does not stand on it. Usually 1/4" per foot. City sidewalks usually slope 2 inches from the street side to the yard side. Make sure your walkway has slope from one side to the other or down the length of the walkway. 1/4" per foot equals 1 inch elevation difference from side to side on a 4' wide walkway.
Now that you know where the walkway will be you can add gravel to get the elevation set for the bottom of the walkway. Whether you dig down or fill up, make sure your gravel is 4 inches from the bottom of the finished top of your walkway. You can drag a 2x4 across the top of the gravel, making sure it is just touching some of the gravel.
Compact the Gravel Base: Rent a vibrating plate compactor at a rental store. They are very easy to use, like mowing the lawn except a little heavier. Simply put it on the gravel, turn it on and push it around.
When you call a concrete mixing plant they will ask you questions about the exact mix you need. There are different mixes for different applications. These are most of the things they will ask:
How Much: Calculate the amount of concrete needed again to make sure you order the right amount according to what you have built on the ground. See Step 2 for instructions on how to calculate concrete amounts.
How Many Bag?: The concrete plant dispatcher will ask you how many bag you want. They are asking how many bags of cement you want per yard. 6 bag is standard for exterior flatwork. 5 bag is often used for footings and foundations. So for your flatwork use 6 bag.
Gravel Size: The concrete plant dispatcher will ask you how large of aggregate you want. You can order anything from sand up to ____. For exterior flatwork you want to order 3/4". This gravel is crushed gravel unless you specify otherwise. Sometimes it is desirable to have smooth stones in the mix for exposed aggregate on the top.
Hot water is used in colder weather, and yes it costs more but most mixing plants will not send it out without hot water because hot water helps the concrete set up properly when it is cold.
Air content: Air is added to the cement by adding a chemical to help form tiny air pockets in the cement that help it better expand and contract when the weather freezes and thaws. Concrete plants in colder regions will add this automatically, but you should ask to make sure.
Slump: The concrete truck driver will put a little concrete into the chute off the truck and ask you if it has enough water for you. More water can be added and mixed up before the rest of the concrete is poured. The slump is a measurement used to determine the stiffness of freshly mixed concrete. The more water that is added will make the concrete more fluid and slump more when it is piled up. More water also makes the concrete easier to rake around and finish. BUT, the more water that is added to the concrete before it hardens the weaker the end product will be. So only add enough water to allow you to work the surface and get a good finish.
There are several ways that concrete can be delivered to your house or jobsite.. Check with your local businesses to see which are available.
Ready Mixed Truck comes in a large concrete truck and is ready to be poured out when it arrives at the job site. These companies have minimum orders, usually 1 to 3 yards. You don't have to use all of the concrete but you will have to pay for it. Call your local ready mix plant to get pricing and details.
Mix On Site Truck comes on a truck that mixes the exact amount after it comes to the job site. This type of delivery is convenient. It may cost more per yard but you will only have to buy as much as you use so the overall cost will be less.
Ready Mix Trailer is a trailer full of concrete that you pick up and tow to your house. You can get smaller amounts at less of a price than the Ready Mix Truck but you have to pick up and take the trailer back. You will need a 3/4 ton truck to tow with, concrete is very heavy.
Pour: Start by placing the concrete in the forms at the far end and back away filling as you go. This is so you don't have to walk or drive thru the concrete after is is poured. Talk to the concrete truck driver to plan out the pour. A good concrete driver will place just the right amount of concrete so that you don't have to rake it around too much.
Consolidating concrete is done by vibrating the surface and edges of the concrete to remove air and rock pockets inside the concrete. This process also brings cream to the surface of the concrete which helps to make a nicer concrete finish. You will consolidate the edges and the surface:
step 9 Strike The Concrete
Screed: The terms screed and strike mean the same thing. After you get down the walkway a few feet with the pouring, take your "screed" board and while using a sawing motion from side to side pull it across the top of the concrete making sure to keep both ends on the form, this ensures that your concrete is the same height as your forms. Screeding gets the top of the concrete very close to the finished elevation. When screeding you should have a small pile of concrete in front of the board that gets pushed along with the sawing motion. Have someone watch the front of the board and add concrete if you have a low spot or take it away if it gets too piled up to pull. If there are holes or dips in the top of the pad you need to put a handful or shovel full of mud in them and screed the area again until the top is flat.
Finish filling the form and Screed the whole surface making sure that the top is flat with not dips or bumps.
The final finishing of exterior concrete is a six step process:
Bull Float: Level it with a bull float or darby. Immediately after you screed the surface you will use a bull float or darby to further level the surface of the concrete. Keep the tool as flat as possible so you don't seal the surface, you want the top of the concrete to show a lot of air holes after you are finished with the bull float.
Wait For The Surface To Stop Bleeding Water: Now let the concrete sit without working the surface. Water will start to come to the surface of the concrete. It is important to not rub the surface of the concrete while the concrete is bleeding because it may cause problems later on like blistering, delamination or dusting.
Edge The Concrete: As the surface stops bleeding you should start edging the edges with a edger. Slide the edger tool back and forth along the form board until you get a smooth rounded edge. If you have a section that won't smooth out or rocks that roll out of the concrete you can scrape some cream off the main slab and fill the holes.
Curing is a often overlooked step in pouring concrete. It is done by keeping the concrete moist. Put a plastic sheet over the concrete the morning after you lay the concrete and leave it on the concrete for 6 to 7 days. Hold the edges down with 2x4 wood or rocks. The plastic will slow the evaporation of water from the concrete which makes the concrete stronger. Concrete takes 28 days to reach its full strength so do not drive a car on the concrete during that time but you can walk on it after a few days if the temperature is above 50 degrees.