Spray in Place vs. Cast in Place

May 3, 2004

by David B. South

Spray-in-Place walls are easier to construct and less expensive than Cast-in-Place walls.

The cost to spray-in-place concrete is approximately the same per cubic yard, as forming and pouring large sections of concrete. The difference is in the volume of material used. The spray-in-place wall will be approximately 3 inches thick. The pour-in-place will be about 8 inches thick utilizing more concrete, rebar and labor and more costly forming materials.

Consider a simple garage wall:

Pouring the footing: In pouring the footing, both systems require approximately the same width and depth (the spray-in-place wall will weigh less), but usually the imposed roof load is the larger weight for the footing to carry.

Forming: Forming for the cast-in-place is to double side form. At a minimum, it requires two layers of form ply and ties and whalers, etc. These forms are at least several times as expensive as a single layer of OSB (oriented strand board -- also called wafer board) for the spray-in-place wall braced with a simple 2' x 4' that can be reused.

Rebar: Spray in place requires rebar. A cast-in-place may not. This decision is made by the engineer, but most walls utilize #3 rebar, 15 inches on center. Since the cost is so minimal, I would use it in either wall.

Note: If the wall is to be insulated we often shotcrete a 3 in. wall, put in cross ties, spray urethane and then shotcrete another layer - forming a sandwich. This is similar to insulated forms with the wire mesh on both sides, yet, in most cases it will be a bit cheaper.

Spray in Place vs. Cast in Place

Consider a simple garage wall:

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