Complex sentence: If the quicklime is slaked with an excess of water then putty or slurry is produced, if less water is used then the result is a dry material (any excess water escaping as steam in during heating).
Split into simpler sentences: If the quicklime is slaked with an excess of water then putty or slurry is produced. If less water is used, then the result is a dry material (any excess water escaping as steam in during heating).