Consolidation vs. Vibration

Question:
Do I need to vibrate my concrete when making countertops?

Answer:
With few exceptions, concrete needs to be consolidated, but not necessarily vibrated.

Consolidation frees trapped air in the concrete and fully encapsulates the reinforcing. During mixing, air is whipped into the concrete, and consolidation helps to remove most of this air. Consolidation is important for structurally sound concrete, and for concrete countertops, consolidation is often done to improve aesthetic quality. What is important to remember, especially with countertops, is that consolidation can occur by means other than vibration.

Vibration is usually used with a high-slump mix and water-tight melamine forms in order to create a surface completely free of voids when the forms are removed. For a stiff mix and when the countertops will have a ground finish, vibration is usually not used. This is because zero-slump, all-sand mixes trap large amounts of air and can require very strong vibration to produce effective consolidation. Even then, the concrete may not become fluid enough to allow all of the trapped air to rise. These types of mixes are usually consolidated by packing them into the forms, rather than by vibrating.

So the answer to “Do I need to consolidate my concrete?” is always “Yes.” The answer to “Do I need to vibrate my concrete?” is “It depends” -- on your mix design and on the aesthetics you are going for.















Large air pockets in the surface of an unvibrated concrete slab.