Half an hour before the plasterer came, I took off the light switch and the plaster round the edge fell away. No problem, bit of thinned PVA, out with the old bag (nearly a year) of Wickes one coat plaster and sorted - it sets in 2 minutes ! But I did wonder - why exactly does old gypsum-based plaster set so fast ? Has the plaster changed or has a retarder degraded letting it set at its natural pace ?
Simon.