Older and Newer Buildings

Older and Newer Buildings

Older and newer buildings have been built very differently.

Using Newer Materials on Older Buildings

As a result of these fundamental design and construction differences, using non-breathable newer materials on older buildings can have detrimental effects, leading to the rapid decay of the weaker, older fabric for the following reasons:

• Moisture: the fabric of old walls can naturally contain significant amounts of moisture. The moisture can originate from multiple sources commonly from the ground (e.g. rising damp, water splashback) or the air (e.g. rain, sea-spray etc.).
• Salts: the fabric of older buildings often contains significant amounts of salts, especially near ground level. Water dissolves the salts from the environment and transports them into the building fabric. Most common sources of salts are rising damp (salts absorbed from the ground), leaks/water ingress (running water washing salts into the fabric), the chimney soot (which contains high amounts of sulphate salts), as well as the air (from sea spray, salty winds or pollution from cars or nearby factories). These salts accumulate over time in the wall fabric and the older the building the higher its salts content.
• Modern non-breathable materials: act as moisture barriers trapping moisture, which can lead to significant moisture accumulation inside the wall fabric. Some modern materials, such as cement, contains lots of additives and salts, which contributes to the damages. The combined effect of moisture + salts through multiple mechanisms start an irreversible degradation of the old wall fabric.

Restoring breathability of the old fabric reduces the moisture content of the masonry which often results in a significant improvement. However, the removal of non-breathable materials does not always fully reverses the masonry's condition to its original condition as damages caused by salts are to a large extent irreversible.

Thus, as a general rule, older (pre-1940s) building should be renovated with traditional breathable building materials. Cement plasters and plastic membranes should be avoided if possible, and for replastering or re-rendering works breathable lime alternatives should be sought.