Surveying for Damp Issues with Historic Buildings.

Building’s fall into two categories for the purposes of surveying for damp. Modern buildings built with a damp proof course and barriers to rainwater penetration, and old buildings built prior to mid to late 19th century depending on the region of the country. Old buildings relied on the walls breathing and shedding moisture before damp became a problem.

In old buildings, walls were built thick enough so that damp could not penetrate to the inside. The masonry bedding materials were always lime mortars or earth. When constructing buildings, the joints were often more porous than the rest of the building elements such as brick or stone. This was so that the joints would drain and shed water by evaporation, preventing long term damage to the masonry. Of all the elements found in a building, the joints were the sacrificial element. As lime and earth mortars are so porous, timber that are in contact with lime mortar is less prone to decay as opposed to when timber is bedded inside of cement mortar.

When built, historic houses did breathe and shed water compared to modern buildings. They were also heated by coal or log fires in an open fireplace which promoted rapid air changes within the building, through air being drawn out through the chimney. Windows and doors were not sealed as they are today which allowed air movement through the building. Internal finishes were lime wash which allowed surfaces to “ breathe “. Although it would discolour when damp, it would not peal from the wall like wallpaper or blister like modern impervious paint.

Over the year’s most historic houses and buildings have been altered to suit our modern lifestyle, nearly always to the detriment of the building. The heating has been changed so we don’t have the same type of air changes. Windows and doors have now been sealed and draught proofed changing the way air flows through the building.

Some of these buildings  have had water from the ground rise into the walls through capillary action. Water from the ground contains salts. Initially for many years the moisture in the walls would evaporate off harmlessly outside during fine dry weather, and inside, because of the rapid air changes induced by the open fire heating drawing air rapidly up the chimney.

When water from the ground evaporates, the soluble salts it previously contained are left in the walls at the point from which it had evaporated. This would be within the surface of the masonry or inside of plaster finishes.

This as an aside is the proof that damp rises. The rising damp deniers  acknowledge that salt bands are found in walls, as do leading and revered conservationists such as John Ashurst and SPAB the society for Protection of Ancient Buildings but none of them can explain how the salts get into the walls other than by moisture rising up the wall and depositing salts when it evaporates.

In time salts block the pores and cause damp to rise further up the walls to evaporate.

A proportion of salts are also hydroscopic and, in humid conditions  will attract moisture to the wall causing a damp area. Sometimes there is a visible salt band and blistering and staining of finishes and plaster caused by salts.

In many old buildings, floors have been concreted over the top of a plastic sheet. This reduces the area of evaporation for moisture from the floor, this can possibly cause more moisture to rise into the walls.

Modern paints and finishes are often applied in place of lime wash further reducing evaporation and compounding the damp issues.

Ground levels are often raised higher than the original, often above the plinth in earth structures, and sometimes above the level of the internal floors. These problems along with defective Drainage, roofing, joinery, rainwater goods, chimneys’, pointing etc., can cause excessive damp in old properties. To compound this problem houses were often painted or rendered externally with inappropriate materials.

Rendering and painting reduce evaporation significantly from the outside surface of the wall, and cause damp to rise further up the wall and to appear on the inside.

Renders crack and allow water to penetrate through, either by capillary action into fine cracks or directly as penetration into larger cracks and de bonded areas. The water is then trapped behind the render and can penetrate to the inside.

 All the above means that by the 21st century a great many old traditionally built houses have damp problems often caused over the last 100 years, by changes in heating and finishes, these damp problems have not been addressed due to a lack of knowledge and understanding of older buildings, traditional materials and the way they work together.

Conservation vs Preservation of Historic Buildings

People buying houses, for the most part, expect the house to be weatherproof with a dry interior. Conservation of houses means they must be owned and lived in to be cared for, which also means they must be fit for this purpose.

How to conserve these houses and make them fit for purpose.

Conservationists want as little intervention into the property as possible, this is so that they maintain any historic fabric and features of the original property. The house and its features can then be preserved and passed down to future generations, which is commendable, but it does mean living in a damp house and most people will not do that.

Many firmly believe when a property is damp, lime plastering and the application of lime wash can reverse the damp problem by allowing the wall to ”breathe”.