Antifoam & Defoamer agents prevent or reduce the foaming tendencies of cement when it is mixed. This is necessary because the properties of cement slurries and the set cement depend on the water/cement ratio. Most field mixers determine the ratio by measuring the density of the slurry, so entrained air causes the slurry to be mixed at improper ratios. Some materials can be used as antifoam agents, but not as defoamers. Other materials act as either defoamers or foam preventers.