Some people are looking for a gypsum style finish on their lime plastered walls. The temptation for some (especially builders) is just to plaster gypsum onto the lime plaster. This is not a pretty relationship between the two and even LaFarge (main supplier of gypsum based products) state that it should not be used over lime plaster / render. So if you are looking for a silky smooth finish what can you do?
It can be achieved in a couple of ways.
1. When the lime plaster is still slightly pliable push in a top coat of lime putty. This is incredibly fine and will be a really smooth finish. If the plaster has dried out too much then you can still apply it, but you will need to give the surface a once over with limewash first and apply the putty whilst the limewash is still slightly damp.
2. Use a clay plaster. This again is a very fine plaster. You will need to slow its drying down a bit as the lime plaster underneath will suck out the moisture really quickly. Using a primer to do this is the best solution. Clay Works in Cornwall have a lot of advice and information on clay plasters. Eco Home Centre will also be running a clay plaster course in the New Year, so look out for that.
These finishes are really fine and also give excellent breathability to the room. If the surface is rubbed against then the main complaint is that you can get dusting from the clay or lime. However this is easily cured either with painting (use a natural breathable paint like a clay paint) or by glazing (a breathable glaze is available from earthBorn – Wall Glaze)