[Nhcoll-l] [External] earthen plaster or clay plaster

[Callomon,Paul]

Just another word on plaster: in many older buildings the wall is built of masonry (brick or block) and is first covered on the inside with a thick "scratch layer" of sand and cement. This is "keyed" or "scratched" while it is wet (scored with the point of a trowel) and then, once it has cured, a much thinner "skim layer" of gypsum plaster is applied over it to create a smooth finish. Sometimes when moisture is present the gypsum, being hygroscopic, falls off the more inert scratch layer.


Paul Callomon MSc
Collection Manager, Malacology and General Invertebrates
________________________________
Academy of Natural Sciences of Drexel University, Philadelphia
1900 Benjamin Franklin Parkway, Philadelphia PA 19103-1195, USA
prc44 at drexel.edu<mailto:prc44 at drexel.edu> Tel 215-405-5096 - Fax 215-299-1170


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