Repairing plaster

[Nemesis]

http://www.cr.nps.gov/hps/tps/briefs/brief21.htm

Judgement should of course be used to decide what constitutes an appropriate repair method and material for any given building.

 

[Gervase]

Trouble is, I've found the US conservation industry to be far fonder of gypsum than we are in the UK, and the national parks are no exception.
The climate, of course, has a bearing on this. Gypsum is hygroscopic, which in the temperate UK can be a problem, but in parts of the US it doesn't matter so much.

 

[Nemesis]

I believe gyspsum may have been used more extensively in the US in the late 19th century; it is not a modern material:


http://www.buildingconservation.com/articles/gypsum/gypsum.htm

 

[Gervase]

Aye, but the yanks seem to use it as a universual gauge on their float coat, while we reserve it for casting and decorative work where fine edges and crisp reliefs are called for.
And, certainly here in chilly, damp Wales, gauging lime plasters with white gypsum from BPB gives you a coat that will suck in any moisture it can get from the air. Touch it on a humid day a couple of months after it's been applied and it will still feel damp.

 

[Nemesis]

Historically it would appear to have had wider use; further research will prove to be interesting and possibly extend understanding of the craft skills and materials used in past centuries.

http://www.plasterarc.net/essay/essay/Joa.html