Heritage ceiling renovation job today. This ceiling is under the second storey of a gatehouse leading to a grade1 listed Manor house. Although under shelter, it’s open on one side and has a large open gateway on the other so almost open to the wind and rain. As with many surfaces in this property, the original distemper, or in this case limewash, has been painted over with a basic white masonry paint. Modern and traditional paints don’t mix.
Modern masonry paints dry to form a fairly moisture-impervious film, they also shrink slightly and this film is then under tension. Modern masonry paints work well when painted on something strong and stable like a cement rendered block wall.
Traditional paints like limewash and distemper are soft finishes that allow moisture to pass through pretty freely.
When a modern coating is painted on top of a traditional one, there is not much for the new paint to grip onto, especially as traditional coatings tend to have a dusty surface. Also, any moisture getting behind the paint film will tend to push the impervious layer of modern paint off.
In the case of today’s job, hairline cracks had appeared in the old ceiling (quite normal in a ceiling of this age) and this probably allowed moisture from the outside air to get behind the paint film and loosen its grip on the ceiling. The masonry paint being under tension has peeled itself back away from the cracks.
The solution in this case is to scrape back the loose and flaking paint and then spray two coats of Elite Heritage, a Swiss-made all-in-one renovation paint designed for churches and historic buildings. Although a solvent-based coating, it’s micro-porous and so will allow moisture to escape. More importantly it dries to a zero-tension film, so if any cracks reappear, the new coating is dimensionally stable and shouldn’t peel.
(In the picture at left, the new coating hasn’t dried yet)There is a slight risk that the masonry paint that is still underneath will fail again in future, but living with this risk has to be considered against the cost of stripping the whole ceiling before painting. I’m fairly confident that now it has been coated with this paint it won’t be a problem.
Published by: Colin Taylor on: Feb 23rd 2016