Admixtures are used generally by addition to the mixing water to alter the fresh and long term properties of cement based mixtures for a specific purpose. The most common admixtures are:

• Plasticisers: Increase the workability of fresh mixes for a given amount of water allowing less water to be used and thus greater long term strength.
• Waterproofers: Reduce the permeability of the mix.

It is essential that the manufacturer’s instructions are followed precisely as overdosing can have serious effects