Solid walls need to breathe
Most older houses have solid walls with no cavity, built from brick, flint or clay lump. Moisture moves in and out of them. Lime plaster and lime render let that happen.
What goes wrong with modern materials
Gypsum plaster and cement render are less breathable. On a solid wall they can trap moisture, which shows up as damp patches, blown plaster, salts and decay in the wall behind.
Where modern plaster is fine
Newer houses with cavity walls and blockwork, and plasterboard walls anywhere, suit gypsum plaster. Most homes built in the last few decades fall into this group.
Living with lime
Lime takes longer to cure and must be protected from frost and from drying too fast. It's a slower job, but it lasts on the right building.
Listed buildings
If your home is listed, check with your council's conservation officer before work starts, as listed building consent may be needed.