I would say that it hasn't increased 20% because 1. if the starting percentage was 18%, you would see a larger precentage but that isn't the case.
The process of “tearing” the fresco off the original wall is called Strappo. Fresco means “wet”. Paint is applied to wet plaster and becomes part of the plaster. This allows the fresco to look virtually the same for over a thousand years, so long as it is not exposed to water or sunlight.
