Plasterers Mate Plaster Retarder is a chemical additive for use with finishing plasters. The additive slows the curing process that causes the gypsum plaster to set or harden. Plasterers Mate is recommended for moderate lengthening of finishing plaster setting times. It will lengthen the setting time by 30-60 minutes depending on the ambient temperature and relative humidity of the environment. Plasterers Mate is suitable for use with the following finishing plasters: Multi Finish Plaster, Finishing Plaster, Board Finishing Plaster