To get air bubbles out of already laid concrete, it is best to _____.

Vibrating concrete is an effective method for eliminating air bubbles that can become trapped in the mixture after it has been laid. When concrete is poured, air can easily become entrained in the mixture, leading to weak spots and reducing the overall durability of the final product. The vibration process helps to displace these air pockets, allowing the concrete particles to settle more closely together and ensuring that the mixture flows into all corners of the forms.

Using a concrete vibrator, the vibration causes the concrete to flow and compact, pushing out air bubbles to the surface. This improves the concrete’s strength and reduces the risk of defects in the finished product.

Other options, such as brushing, rolling, or stirring, do not provide the same effectiveness in removing air bubbles. Brushing the surface would not affect the depth of the concrete or impact the trapped air beneath the surface. Rolling could potentially lead to further mixing of the concrete but does not effectively displace air bubbles. Stirring may even introduce more air into the mix rather than removing it, which is counterproductive for achieving a solid and durable concrete structure.