Can You Pour Concrete Over Existing Concrete?

One of the most common questions we get is "Can you pour concrete over existing concrete?" The answer is yes but you need a minimum of 5 inches to work with to pour a new slab over an old one.

Obviously this wouldn't work for driveways and most sidewalks. It can work for some patios and porches as an alternative to ripping out and replacing the old one. But in order for this method to work, the thresholds of any doors has to be several inches above the old concrete.

Before pouring new concrete over existing concrete, you need a buffer between the two slabs. A minimum of 1 inch of granular fill, such as sand, is needed to maintain a separation between the two so they can move and shift separately from one another.

The standard thickness for residential concrete is 4 inches. If you're adding a 1 inch buffer and 4 inches of new concrete, then the height of the patio/porch is raised at least 5 inches. With some extra rebar or wire mesh, you can probably get away with 3 - 3 1/2 inches of new concrete.

You can also increase the size of the patio as well. Dig out any grass where the new concrete is to be poured and set forms 5 inches above the old concrete. Fill it in with a gravel/sand base leaving 4 inches for the new concrete. Place rebar every few feet to create a bridge along the outer edge of the old concrete. That outer edge is a good spot for cracking due to the sudden change in the subgrade.

If there isn't enough room to pour new concrete on top, then consider an overlay before replacing the existing slab.

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