How to Determine the Correct Thickness of a Concrete Patio Slab

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What You'll Need
Concrete Slab
Tape Measure
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2 by 4 timbers

If you want to lay a patio using a type of concrete patio slab, then it is generally a good idea to begin the process by working out the thickness of the concrete slab that you will need for your patio. This can sometimes be a calculation, or it might be learning the type of thickness that your specific patio slab will need to be. However, knowing the thickness of your patio slab is vital to the project, as they can affect the size of the corner brackets and also how much concrete you will have to lay down in order to ensure that the slabs stay in position for years to come.

Work Out the Ratio

Before you can do anything else, you will need to work out the ratio of concrete thicknesses. The thickness of the slab will need to be slightly smaller than the area of the hole that you have dug into the earth to accommodate your slab. The depth of the hole will also have to be filled with gravel, a depth of about 4 inches is the industry norm. It is also considered acceptable to have a patio slab consisting of 50 percent concrete, and 50 percent gravel base. The half-and-half ratio makes it considerably easier to work out the correct ratio of your concrete. While digging the patio, you should also consider other options, such as the position of the concrete slab in relation to grass and soil.

Fitting Concrete into the Ground

Lay a concrete slab completely into the ground so that it is level with either your topsoil or any grass that is above it. The advantage of laying your slab in the ground is that you can add a greater thickness to your concrete slab, as this will be supported not only by the gravel base but also by the surrounding turf. You may choose to add an extra 1-2 inches of concrete to your slab in order to make it better able to support the weight of people standing or sitting upon it.

Fitting Concrete Above the Ground

If your slab is to be fitted above the level of your topsoil, then you should consider a slightly thinner amount of concrete to be used upon it. The concrete can be 3-4 inches high, supported by a gravel base of 4 inches. When you make a concrete slab that is thinner than average, you will need to adjust your ratio of water to cement in order to get the proper denseness to your slab.

Considering Joints

With a larger than average set of concrete slabs, you should consider installing concrete joints. These will support the concrete patio slab and will need to be a quarter of the depth of your slab. For example, a 4-inch patio slab will have a 1-inch concrete joint. When working out the proper thickness of the slab, you should take the appropriate size of any joints into consideration.