Rebar, or reinforcement bar, is perhaps the most widely recognised building material in use – yet whilst the ordinary person in the street might know what it is, many people underestimate just how vital it is to building projects of all sizes. In this article, we’re going to take a look at how rebar and reinforcement mesh are used within concrete slabs, and we’ll answer some common questions about concrete slab reinforcement.
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Perhaps the most widely asked question is whether you need to reinforce a concrete slab at all. The answer to this is that it depends on the depth of the concrete being poured and the purpose of the slab itself. Generally, if you intend to pour a slab that is more than 4-5 inches deep, you should use a reinforcement product such as rebar or reinforcement mesh.
Again, this depends on several factors, including how the slab will be used. If the slab is beneath a small potting shed, for example, where there will be very light use and no significant weight put on the slab, and the slab itself is of a sensible thickness, then serious cracking is unlikely. However, adding rebar can still be a good idea, even in projects that do not technically need it, since steel reinforcement will add significant tensile strength and reduce the chances of cracking. Wire reinforcement mesh is a straightforward alternative to rebar rods in concrete slab projects.
The placement of rebar or reinforcement mesh within a concrete slab depends on whether it is being used for structural strengthening or to mitigate against shrinkage and cracking. If the reinforcement is intended to add structural strength, it will be placed lower down within the slab depth than if its purpose is to reduce cracking because of shrinkage or temperature change.
Rebar and reinforcement mesh should be laid out for consistent coverage of the whole slab area, and should be supported and tied together in order to prevent movement as the concrete is poured. In order to prevent a height buildup where panels of mesh overlap, flying end mesh can be used – this has one length of rebar removed along one edge, so that there is no additional height on the overlap.
There are pros and cons to both types of reinforcement, and the best option may well vary from project to project. Rebar will inevitably take longer to install than reinforcement mesh, so will cost more in terms of labour. However, rebar is generally stronger than mesh, so may well be a better choice for projects that require additional structural strength within the slab.
Calculating concrete slab reinforcement
It’s important to work out exactly how much reinforcement your project needs, to avoid wastage or lost time caused by ordering insufficient quantities for your project. To calculate the amount of reinforcement needed, you’ll need the length and width of the slab, along with the spacings between rebar rods. Obviously if you are using mesh instead of rebar, then the spacings are already taken care of. Once you have these figures, it is a simple process to work out the quantities needed.
As well as working out how much rebar or reinforcement mesh is needed for a project, it can be useful to know how much the total reinforcement will weigh, and our handy rebar weight calculator can help with this, providing accurate figures that can be used to verify deliveries, and to ensure that vehicles are not overloaded.
Whilst some light-use slabs can be built without reinforcement, wherever possible it is a good idea to use mesh or rebar – either to strengthen the slab itself, or to reduce surface cracking. Whether or not to use concrete reinforcement is a decision that needs to be made on a project by project basis.
We are sometimes asked whether it’s possible to use other products in place of rebar or reinforcement mesh. Suggestions have included chicken wire, fencing wire, fiberglass cloth, and plastic mesh. None of these products have the strength, consistency and resistance to corrosion and degradation that rebar and reinforcement mesh have, and they should never be used as a replacement for approved reinforcement products. At best, they will have little to no effect, and at worst, they could compromise the integrity of your concrete slab.