Concrete Slab Design

In commercial construction concrete slab design is a job strictly done by such professionals as architects and engineers. During slab design process, architects are responsible for the final cement floor finishing, shape, color, and type of finish of such item as concrete patio slab and cement floor slab.

Structural engineers on the other hand determine concrete slab thickness, type, size, and spacing of reinforcements, type of concrete mix, size of gravel, number of cement bags, slump, etc. It is only after the design is completed that the contractor puts together cost concrete slab based on the design.

In residential construction especially home improvement type work, this process is heavily dependent of the contractor’s experience. In most cases the process works like this, a homeowner needs a concrete patio at the back yard. He calls a few contractors for bids, pick the lowest bidder give him half money upfront, as most small concrete contractors require in order to begin working, that’s all the design involvement of the owner. The contractor will then decides or “design” the following: concrete slab thickness, wire mesh reinforcement, bag mix, slump, size gravel in the mix, broom finish, drill dowls into existing house if applicable, etc.

Since typical homeowners know very little about concrete, these design issues are the contractor’s responsibilities and the decisions are solely based on experience which can be very deceiving because it is very difficult to verify contractors that have good experience.

From design perspective here are the answers to design issues mentioned above. Slab thickness, always use minimum of 4 inch thick slab for driveways and patio. For concrete basement floor or any floor slab, use minimum 3 inch thick.

Mix design, use minimum 3000 psi (5 bag mix) for floor slabs and any concrete exposed to weather use 4000 psi (6 bag mix). As far as reinforcements, unless my customers insist on reinforcements I normally pour unreinforced floor slabs, driveways, patio, and sidewalk. For finish, use broom finish for driveways, patios, and sidewalks.

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