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How to Form Concrete with a Rebar Grid

There are so many applications that come to mind when I think of the uses for concrete, particularly when reinforced with a rebar grid. You have the option of using a concrete slab as a countertop or to create a uniform stoep or porch. As well as creating steps, flooring in workshops and in garages.

First though it is best to get a handle on the basics before making large commitments. Come with us through this article as we take a step by step look into how to form concrete with a rebar grid. As a driveway is a fairly common part of someone’s property that would use concrete with a rebar grid.

First Considerations

As you may have guessed, though the steps are easy enough to set out there are still a few considerations to keep in mind. The intended use of the concrete slab will influence the thicknesses of the concrete and the area that needs to be prepared.

Keeping with our chosen example of driveways it is clear that the intended use is for vehicles to drive over and potentially park on as well. Take into account what vehicles will be using the driveway. Large vehicles have a greater impact as well as the frequency of driveway usage.

With an idea of the expected load that the driveway will need to withstand you can now survey the area the driveway will be placed. Place out temporary posts or stakes to outline the area for the driveway. Then measure the area, check the slope of the land, and take note of what soil you are working with as they will all determine the work and process going forward.

Safety Gear

Before we jump into the actual steps, I wanted to take a moment to take about safety. Safety gear is essential in all building projects. Wet concrete can have some nasty effects when it contacts your skin that range from mild redness to chemical burns. Be sure to have and wear the following safety gear at the very minimum:

• Rubber gloves
• Tall rubber boots
• Eye protection

Step 1: Permits & Pipelines

Like most of us you probably live within a governed area that has rules and regulations that supply the public with guidelines for erecting buildings and roadways. So other than gathering safety gear the first thing you need to do is find out if and what permits you require for your building or driveway.

At the same time as acquiring your permitting, if required, you should get a map or municipal representative to give you a map of where municipal lines run so that you do not dig into anything serious. It may seem like a bit of a mission, honestly though, it really is in your best interest to be as prepared as possible to avoid accidents and unforeseen costs.

Step 2: Prepare the Site

Now that you have your area and permits where needed preparation of the site can begin. This is an exciting time as it is the first real step in getting your driveway done. It is still important to keep focused as the decision for how to proceed with the site prep will affect the time it takes, and the cost of the project.

The slope of the land and the soil are now factors to consider for your driveway build. A significant slope will leave you with some choices. The first being to level the slope out which requires moving lots of soil. The second being to build up the low side which means bringing in soil. Lastly you could look at digging into the high side as well as building up the low side to bring them to a point that is workable. Keep in mind that a low retaining wall on the high side is likely necessary to keep the rest of the soil back. Though you may also consider shuttering, a temporary mould for the wet concrete.

Step 3: Boards for the Form

If you have ever done any home DIY work with cement or concrete, then you probably know about forms. When you need to pour concrete, it usually requires a form of some kind that will be essentially ripped off of it once it has finished setting.

Typically, wooden boards are used for the frame that makes up the form for the concrete. Different areas have access to different materials so I would suggest speaking to a professional builder or watch some videos for advice on what materials to use. Be sure to choose budget friendly material. Once you have your boards get them into to place in the dug up/built up area of your site. Use a builder’s level to make sure your boards are level so that when they come together as a frame, it will be the ideal form.

Step 4: Calculate the Fill

The form is in place, and you have a very empty open block and some of the form edges may have gaps underneath them. This is when you start to calculate the fill that you will need before moving on to the rebar grid and pouring the concrete.

Measure the length from the top of the form to the ground on the inside of the form in a few spots, up to 5. Get an average measurement and then subtract the expected thicknesses of the driveway. This will tell you the volume you need before the next steps. You want to be sure that the fill will provide a firm base but also supply a good amount of drainage.

Step 5: Time for the Rebar Grid

Rebar is reinforcing steel bar used to provide tensile strength in concrete structures. In simple words, it stops concrete from cracking so easily. In something you want to be able to take a significant load, it is definitely desirable to ensure that it has the capability of doing so. Rebar is not hard to come and well we happen to experts on the matter so if you are looking for rebar do give us a shout.
When you procure the rebar that you need make sure to get a roll of binding wire and a tie-wire twisting tool which you will need to connect the rebar. Place rebar vertically and horizontally in the form to make a rebar grid. Connect the rebar where it overlaps with the tie wire. Cut and bend the rebar as needed or we will happily do it for you (do follow us on LinkedIn and Facebook for our next article tackling the cut and bend aspect of rebar). There is a little item referred to as a chair that provides a great amount help. The chair will sit underneath the cross point of the rebar to lift the rebar and allow the rebar to have a centred distribution throughout the concrete slab.

Step 6: Dampen the Base

Alright, so we have the base filled and the rebar grid in place. There is one small step to do before the actual pouring of the concrete. Dampen the base with a hose. Creating a dampened area for the concrete will prevent soil from sucking out water from the concrete as well as extended the curing time. A longer cure time equals a harder driveway.

Step 7: Time for Pouring

Try to pick a day that is not hot or windy as this leads to faster drying and quick curing. Not the best for concrete slabs. Steer clear of rainy days as well, a day like that will ruin the concrete mixture. If a truck is involved, then be sure to mark out the route beforehand. Have two trusty wheelbarrows on hand and a team of strong helpers. About 4 or 5 should do the job nicely.

A good tip is to use a drier concrete mix. Though it is harder to get into the form a drier mix will ultimately lead to a stronger surface that is more crack resistant. Begin by pouring the concrete in sections. This will give you a spot to concentrate on and make for manageable amounts of concrete. While also preventing the concrete from getting too heaving to smooth out at the end. Place the concrete into the section with a concrete placer or a tool that will let you shift the concrete in the form. Use the tapping method to get the wet concrete to place correctly.

In this step other members of the team will manage the initial levelling where a screed board is used. A stretch of wood slightly longer than the width of the form is usually good for a screed board. The purpose is to remove excess concrete. The screed action is slowly moving over the placed concrete with a back-and-forth motion to catch any extra concrete. It would be advisable to repeat the screed board action several times to maximise the results.

Step 8: Smooth the Top

Smooth over the top with a neat tool called a bull float. What a fun name. This is a tool with a long handle and a large flat piece at the end used to smooth the top of the concrete. This does take a little practice and patience. The bull float pushes larger aggregate down away from the surface to prevent chipping. The aim is to remove any marks from the screed session and fill in any low spots. Too much use of the bull float could lead to a weakened surface, so it is recommended not to exceed 5 passes.

Step 9: The Finishes

For the finishes touches you begin by rounding the edges and then using a hand float to smooth out any markings made by rounding off the edges. Then make grooves into the concrete horizontally. This will create a weakened point for the inevitable shrinking of concrete during curing to happen in these spots versus random ones. In this particular example you will want to optimise the surface for traction as it is a driveway. This is done my making a slightly rough finish with a method called brooming. More on that to come in future articles.

I hope you have enjoyed this walk through the steps of how to form concrete with a rebar grid.