The Problem Clinic for April had an article on removing heavy efflorescence. Is it possible to receive any additional information on this method, such as time required, thickness, and how the papier-mache is actually made?
The information we have regarding the removal of efflorescence with papier-mache is more art than science. Pulped paper would really be a more accurate term than papier-mache, since no glue or lacquer is used in the mixture. Old newspaper is crumpled and put into a plaster or mortar mixer with a small amount of water. The mixer is started and additional crumpled paper added one sheet at a time. Proportions of water and paper are adjusted to get the maximum pulping action. When the contents become a pulpy mass they are removed and plastered onto the wetted wall as described in the Problem Clinic article. If the pulp is too wet to stick it can be wrung out by hand, or if too dry it can be moistened further. Any practical thickness is satisfactory - perhaps about one-half inch. Time required before peeling depends on wind, humidity, temperature, and the amount of water absorbed by the wall. One week per application might be a good average in dry weather.