Concrete Slab | What is the Tolerance levels for Concrete Slab Thickness

A concrete slab is the most common structural element of modern buildings. Concrete slab is used for flooring, rooftops, foundations etc. The concrete slab thickness is a very important matter when you are building a house or any concrete structure. Thickness of the concrete slab has been a contentious issue for quite some time. The tolerance level of the thickness of the slabs was changed in the year 2006. For on ground slabs there is no maximum tolerance. There is simple minus tolerance, which means that further thicker slabs have not been prohibited by the specifier. According to the official tolerance, that every sample should be more than ¾ inch thicker than the specified thickness and the overall average of all the slabs put together cannot be more than the specified thickness i.e., 3/8 inches. This amendment in 2006 is different from what was mentioned in 1990. From 1990 till 2005 the thickness tolerance was set at +3/8 inch, -1/4 inch. The tolerance which has been set as a yardstick in 2006 is nothing more than an average and a minimum thickness level which has been made the benchmark. Contractors should be careful about how thick the slab should be to ensure that it is not thinner than the specified measurement of ¾ inch.

According to experts, these tolerances give owners, engineers and architects false expectations as there are an extremely limited number of slabs that have ever met these criteria. It has been seen that slab thickness variations usually don’t result in strength problems. It is often seen that in case of slabs on ground a decrease in thickness of the slab is generally made up by in place higher concrete strengths and sub grade k-values than which are considered in the design. Based on current practice contractors provide a concrete slab thickness, which meets tolerances for 50% or more of the slab area.

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