Gwynne Anthony 2020

ART506 Dissertation 2019. Anthony Gwynne . 123 Appendix K: Damage caused by the trapping of water K1: Efflorescence (Everett and Dean. 2000. Finishes- Mitchells Building Series . Oxford: Routledge). Efflorescence is a crystalline deposit of salts that can form when water is trapped in or on brick, concrete, stone, stucco or other building surfaces. It has a white or greyish tint and consists of salt deposits left behind when water evaporates. In addition, efflorescence can appear as a powdery substance on floors and walls and requires special care to treat. The movement of moisture upward through permeable building materials by capillary action is called rising damp and it becomes a problem if the moisture penetrates vulnerable materials or finishes, particularly in the occupied parts of a building. This moisture can dissolve soluble salts from the building materials such as calcium sulphate and may also carry soluble salts from its source. If the moisture evaporates through a permeable surface, these salts will be left behind and form deposits on or within the evaporative surface. Where there is a large evaporative surface, salt crystals are deposited as a harmless flour-like dusting on the surface and this is termed efflorescence. If evaporation is restricted to localised areas such as defects in an impermeable paint finish, then salt deposition is concentrated, forming thick crystalline deposits with the appearance of small flowers; hence the term 'efflorescence'. K2: Crypto fluorescence (Everett and Dean. 2000. Finishes- Mitchells Building Series . Oxford: Routledge). When evaporation of trapped moisture occurs within the material, salts can be deposited within the pores. The expanding salt crystals in these locations may result in fractures forming in the material and spalling of the surface. This is termed crypto fluorescence. This type of decay may be seen in porous brickwork or masonry. When there has been a long-term problem with moisture penetration, evaporation at the edge of the damp area leads to a distinctive 'tide mark' as a result of salt deposition. Where this occurs at the base of a wall, the tide mark is often taken as a typical diagnostic feature of 'rising damp'. However, these salt accumulations may remain even when the water penetration that originally caused them has long gone. Similarly, water penetration may have occurred from causes other than 'rising damp'.