Permeable lime-based materials for conserving or treating porous building materials including limestone, soft brick, and calcareous sandstone. Sheltercoats are individually designed to match the colour of the material to be treated, and are sacrificial coatings with the primary function of protecting the masonry beneath. Properly applied to appropriate materials they prove durable in sheltered locations. They comprise lime putty and fine stone-dusts, and occasionally natural pigments. Lactic acid casein, a natural glue, is added to improve adhesion and durability. Internal and external use.