Research and Technology: Slabs on Grade, article available for download

[The following article is a summary of a more complete article by Alan Schambach, PE, FBi Buildings Inc., and Terry Feldmann, PE, Maurer-Stutz, Inc., on the subject of slabs on grade available for free download. CLICK HERE TO DOWNLOAD THE COMPREHENSIVE ARTICLE…]

How thick should I pour my floor? Do I need reinforcing? Which type of reinforcement is best? How much load can I put on it? Will my fork truck crack it? Do I really need joints in my floor? Should I install a polyethylene vapor barrier or vapor retarder underneath the whole slab? What about insulation? Do I need rock underneath? And how much do all these things matter?

Have you ever been asked those questions? Do you have answers to them? If not, where do you turn? This article aims to inform the building designer, contractor and owner about many important issues in the design of a concrete slab on grade.

Understanding the use of the slab is of primary importance. The frequency and size of vehicular traffic can play a significant role in the required size of the slab. The need for the slab to be part of a containment vessel will force a close look at reinforcing, joint detailing and waterstops, among other things.

Like our post-frame buildings, a slab on grade is only as good as the soil supporting it. Learn some dos and don’ts regarding site preparation, drainage, and materials and how the type of fill can affect the required control-joint spacing.

How many control joints do I need? Why do I want cracks in my floor? Concrete will crack, and the role of the designer is to make sure that there is controlled cracking at predetermined locations, as opposed to the random cracking that would occur if control joints were not installed. Learn how the amount of reinforcing in the slab can affect decisions on the number and spacing of control joints.

Proper curing of the slab is also important for long-term performance. How many post-frame builders have had customers complain about their building sweating in the fall? Could it be a result of the concrete floor poured a few weeks earlier?

Can slabs move? They certainly can. In this article you’ll find some points to consider regarding how slab movement will interact with your building, ways to prevent some detrimental movement and a few thoughts on insulation.

Terry Feldmann, PE, is an agricultural engineer at Maurer-Stutz, Inc., in Peoria, Illinois. He can be reached at

Alan Schambach, PE, is a structural engineer at FBi Buildings, Inc., in Remington, Indiana. He can be reached at


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