When mounting a pump and driver, an acceptable formula for grout consists of:

The correct formulation for grout when mounting a pump and driver is a mixture of one part cement to three parts sand with a minimal addition of water. This ratio offers a balance that provides the necessary strength and stability for the mount without being overly fluid, which could impair the grip and support.

Using one part cement ensures that the mixture has adequate binding properties, while three parts sand contribute to the overall bulk, giving the grout a solid foundation without compromising its integrity. The minimal water included in the mix activates the cement and aids in achieving the desired consistency.

The other formulations presented would not provide the same desirable characteristics; they either result in a mixture that is too wet and lacking in structural integrity or do not harness the right balance of grip and strength necessary for securing pumps and drivers properly.