Normally this is caused due to insufficient cement being mixed into the plaster. It can also been caused by too much moisture in the substrate that has not been allowed to escape.
Solution:
- Ensure that the surface is dry.
- Brush the friable plastered areas with a soft bristle broom, to remove the bulk of the loose cement plaster.
- Apply two coats of Prominent Surface Restorer, the first coat diluted 15% with turps, allow to dry for 8 hours and apply the second coat undiluted,
- Allow drying for 24 hours.
- This system must not be used on floors. The topping will have to be redone.
- Apply the selected Rainbow Paints topcoat.