Having been using my own recipe JB Lime Finishing Plaster for over 3 years now on all sorts of jobs from renovating old multi surface painted walls to new work on lath, stone, woodwool board and plaster board I have now developed a 2 plaster system in which the standard JB Lime Finishing Plaster is levelled and compacted using a felt float
but rather than smoothing this with a steel trowel I apply a final coat of micro fibre reinforced lime putty – anything up to 2mm thick, often in two passes to achieve a really smooth finish. Not perhaps what is required or even wanted all of the time but when patching a lath and plaster ceiling or plastering up against smooth gypsum plastered walls, a really smooth finish is definitely desirable.
In this particular job the walls were damp and the paint peeling off, on investigation it turned out to be that the plasterboard was stuck direct on to a thin cement screed applied to the brick and stone built wall. The damp was travelling through the plasterboard adhesive and damaging the paint as well as rusting the angle beads.
I replaced the effected plasterboard with wood wool board fixed to battens so that the boards are not touching the salty masonry, I then plastered the woodwool board using the technique I describe above. This is a kitchen and the other walls are gypsum.
Now that the plaster is separated from the salty masonry by the woodwool board the salty damp problem should be cured.