Key concepts in sustainable building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 80

It can be seen, then, that natural materials' 'breathability' maintained the structure of the
building in good 'health' and ensured that the thermal performance of the fabric was not
compromised. Unfortunately, in the second half of the twentieth century, the cheap availab-
ility of synthetic materials - which are usually not vapour permeable - and the widespread
use of very hard cement renders and mortars externally, and gypsum plasters and non-
vapour-permeable paints and varnishes internally, led to some ill-advised 'repair' work to
older buildings. The application of inappropriate materials often stopped the 'breathing'
wall from working properly and resulted in damage to the structure. Only in recent years
have we understood the damage done to our older buildings in this way, and begun to put
right the mistakes of the past.
Figures 1 and 2, on the following two pages, show a traditional breathable solid wall in
good working condition and what happens when things go wrong.