Building Pathology is a catch-all phrase used to describe the problems which happen to a building as it weathers. A huge industry of misinformation has built up around the subject. The Timber and Damp industry, headed by the Property Care Association has defrauded Britain's public since the 1960's with it's use of damp proofing and chemical application, rather than promoting a sensible understanding of why problems occur.
Building Pathology revolves around two main variables: Temperature, and Moisture. The interaction of these seemingly innocent variables can wreak havoc with a building - old or new. We have undertaken extensive research ourselves, building on a huge database of surveys and personal experiences - this, together with our scientific knowledge and experience, makes us some of the most capable building pathology experts in the country. We use a variety of equipment to help us understand what is happening to buildings: Infrared Thermography - using FLIR Thermal Imaging Cameras shows even the smallest variations in the temperature of building fabric. Thermo Hygrometers from industry leaders, Vaisala - are used to analyse the actual moisture content of the air in and around buildings. We monitor the environment of a building to build an understanding of where moisture is coming from, and why.
We do NOT use damp meters. Some so called experts claim that damp meters have a place in building pathology. They do not. They measure conductivity of materials - NOT dampness. The ONLY thing a damp meter can tell you is that something is totally non-conductive, and therefore dry. A zero reading means there is no moisture. A 100% reading can also in all likelihood mean there is no moisture as well - but that the substrate being tested is conductive - this might be chemically treated timber, salt contaminated plaster or mortar, foil backed wallpaper, lead based paint, or organic materials like hair or straw.
Chemical or gravimetric analysis of building materials also gives us total moisture content - brick, stone, mortar and plaster can be analysed in this way to gain an understanding of how much water is present. It does not tell us where the water is from - generally this diagnosis comes from an in-depth understanding of the entire building environment.
To understand what is happening to a building, we need a thorough knowledge of the original construction, the materials used, and their performance characteristics. This leads us through a sometimes complex detective investigation to record and understand the changes that successive generations have made to the building. As modern materials have been introduced, breathability (vapour permeability) is reduced, resulting in entrapment of moisture, and start of the decay cycle.
BS 7913: 2013 is a basic guide to some of the principles involved - it sets out some of the cornerstones of any Building Defect survey - but is no subsitute for thorough, in-depth knowledge of the issues.
A good working knowledge of geochemistry is essential to understand the reactions taking place in old buildings as water affects various building materials and contaminants. These days, we have to deal with pollution not just from traditional sources - such as fossil fuel fumes in chimneys, but the extensive damage caused by nitrates from diesel vehicles which cause much of the crumbling stone and white staining we now see at low level on buildings in towns and cities.
Much has been written about moisture 'rising' in buildings. This almost never happens - nor does the oft repeated 'capillary' rise. The real process which underpins moisture movement is diffusion. The air around us contains water, oxygen and nitrogen - of which water is the lightest. These molecules can move through the smallest of gaps in building materials with ease - it is why doors stick in their frames, and timber floors become uneven. It is not a problem until this water changes from being a gas, to a liquid - it condenses. Condensation is driven by 'Dew Point' - the temperature at which water as a gas turns to water as a liquid. If a wall is cooled below Dew Point - it becomes damp - water forms in pore spaces just as fog forms. If no barrier to evaporation is present, this water can easily evaporate as conditions change. If the wall has modern impermeable coatings - cement, gypsum plaster, tanking, varnish, plastic paint - it stays wet, and the wall starts to degrade, with salts rapidly forming which accelerate the decay.
It's not all about bricks and mortar - timber also decays - and we know a lot about timber and how to prevent decay. The same principles apply - let it breathe, and it stays dry and will not rot. Trap moisture into it - by painting with gloss plastic paints, or varnishes - and timber will rot rapidly. Expose floor joists to high levels of humidity from an unventilated cellar, and they will be vulnerable to beetle attack.