Important Renovation Points for Old Buildings

Due to their design, age, lack of damp proof courses etc. the fabric of old buildings always contains moisture. In order for the wall fabric to stay healthy and dry, it has to be able to eliminate its moisture. This function is achieved by design by the conscious use of specific building materials which are breathable or vapour permeable. Virtually all traditional building materials - e.g. bricks, timber, lime plasters - are breathable, allowing the natural evaporation of moisture from the damp fabric.

From the second part of the 19^th century (also known as the Industrial Revolution) a gradual but major shift occurred in building materials. Older, breathable traditional materials have been gradually replaced by modern non-breathable materials. One of these materials was Portland cement. During the late 19^th century, this new material with much shorter drying times carried the promise to revolutionize construction, allowing a much faster completion of building projects. However, a 100 years history of this material has taught us that modern cements do not work well in aging or old buildings. They trap moisture leading long-term to severe dampness problems. During the past few decades an increasing number of plastic membranes have also been used in construction, making moisture damages even worse.

Today, most mainstream renovation materials available are modern, non-breathable materials primarily designed for newer buildings, which do not work well in old buildings. They trap moisture, leading to many dampness problems.

In order to prevent such problems and make long-lasting renovations, old building owners must educate themselves in these matters, understand the importance of breathability, the differences between breathable and non-breathable materials and make conscious choices of renovating old buildings with traditional breathable materials. Avoid cement plasters and plastic membranes and use lime plasters instead.

With the increase of energy prices there is higher demand for thermal insulation than ever before. The thermal insulation of older buildings however is a completely different proposition from the insulation of newer buildings. Here is why.

The insulation of newer buildings is only about thermal installation, so any good thermal insulation material will do it.

The insulation of older buildings however is about thermal insulation and moisture management. Because the fabric of older buildings contains moisture, consideration must be given to the moisture management aspect of thermal insulation. 

There are a multitude of thermal installation materials and solutions on the marketplace however most of these have been developed for newer buildings with a dry fabric with no need for moisture management. Hence, modern thermal insulation solutions are non-breathable. When they are applied onto old buildings they block the evaporation of moisture, causing future moisture problems and potential mould growth under the thermal insulation.

The topic of salts and problems caused by it are probably one of the most overlooked and unknown aspects of building conservation. Conservation professionals talk a lot about dampness and very little about salts. The interesting fact is that a lot of dampness problems are in fact a combined dampness and salts problem. This is a very important technical point that can be very easily overlooked, resulting in some very costly repair mistakes.

Often water that looks like water is not just water. Water often carries dissolved minerals known as salts. Water rarely causes damages on its own. It comes in then from a breathable fabric it evaporates without a trace. However, salts change the game. When water evaporates, the salts stay behind and crystallise. During crystallisation salts expand 5 - 10 times in volume and the physical expansion breaks down the wall fabric. Crumbling is caused by salts not high humidity. 

Water on its own is mostly harmless. Water mixed with salts becomes a deadly weapon, irreversibly damaging the historic building fabric. It is not commonly known that modern cement plasters also contain salts. Salts are added to cement plasters during the manufacturing process to slow down its drying time, to keep cement workable for longer. The high salt content of cement is another reason to stay away from it.

The whole topic of salts is discussed in great detail here, however, as a quick summary, here is how salts can affect (negatively) old buildings:

• Salts make the masonry damp: salt molecules can easily attract water, bonding moisture from the environment electrochemically through hydroscopic (water-attractive) action. Thus, under the same conditions, a salty masonry can accumulate and contain much more water then a non-salty masonry.
• Salts keep the masonry damp by reducing breathability and limiting evaporation: due to their electrochemical charges, salts trap moisture and do not let it go easily. It takes a significant amount of energy to separate water from salts, a salty masonry this staying damper for longer and drying much slower than a non-salty masonry. 
• Salts make the masonry crumble: during drying, when the water evaporates and the masonry dries, salts recrystallise and expand, causing crumbling, delamination and irreversible damages to the historic masonry. The damages shown below are all caused by water and salts, not just plain water.

As we can now see, the topic of salts is very closely related to the topic of moisture. Salts make moisture problems significantly worse than they would otherwise be. Thus, the effect of salts must be well known, understood and mitigated with special plasters developed for this purpose - which brings us to our next important point.

Although regular lime plasters are breathable and suitable for a wide range of plastering and decorative applications, they have limitations. In the presence of increasing dampness and salinity the life expectancy of lime plasters decreases quickly. Hence, in damp and salty environments, despite their breathability, regular lime plasters won't last very long.  

By adding volcanic sands and ashes (natural pozzolans) to the lime, the Romans have developed a wide range of lime plasters for a very wide range of specialist applications - including waterproofing applications which today are commonly solved with modern Portland cement. These special lime  plasters present a building-friendly alternative to cement plasters. Some of these Roman lime plasters were able to set underwater, being suitable for very damp environments. The longevity of these plasters was also outstanding, many of them lasting for centuries.

The Rinzaffo MGN lime plaster, based on an old Roman recipe, uses lime and a variety of volcanic sands and ashes. The resulting mix retains the open pore structure of lime resulting in high breathability. The volcanic ingredients make the plaster highly resistant to dampness and salts, making these Roman mortars perform extremely well in damp and salty environments.

Using these Roman specialist lime plasters in damp, humid or salty environments results in significantly longer lifecycle of the lime plastering without affecting the breathability of the wall fabric. These lime plasters have been used for centuries in marine and coastal areas, including Venice, and are heritage and listed-building compatible materials.