پديد آورندگان :
پيرك، مهدي دانشگاه آزاد اسلامي، واحد تهران مركزي - دانشكده هنر و معماري , عبدالله خان گرجي، مهناز موزه ملي ايران , وحيدزاده، رضا دانشگاه آزاد اسلامي، واحد تهران مركزي - دانشكده هنر و معماري - گروه رشته مرمت , بهادري، رويا پژوهشگاه ميراث فرهنگي و گردشگري
كليدواژه :
بناهاي تاريخي , شوره زني , نهان شكفتگي , عارضه ي نمك , آسيب شناسي , حفاظت و مرمت
چكيده لاتين :
This paper is based on a research on the problems of salt attack and rising damp in heritage
masonry buildings. Amongst common building defects occurrences in heritage buildings, salt attack
and rising damp are considered as the most challenging, particularly in building conservation. Rising
damp and salt attack, a worldwide phenomenon, are major causes of decay to masonry materials.
Moisture and salts in masonry walls can result in damage. The presence of water-soluble salts in
porous building materials is one of the principal problems of conservation. Salt attack and rising
damp together pose a serious threat to buildings especially with regard to load-bearing walls
constructed of brick, stone and mortar. The problem of salt attack is closely associated with rising
damp. On its own, rising damp can make buildings unsightly and unpleasant to occupy. The
situation is made much worse if there are appreciable quantities of soluble salts present, because the
rising damp will carry salts up into the masonry to where the damp evaporates. Moisture from the
rising damp makes the salts existing in the building material soluble, or the ground water which
contains salts finds its ways through the building wall. Salt damp is caused when moisture from the
ground is carried up into the wall of a building. This process involves the movement of water from
a high concentration, being the ground, to a low concentration, being the porous wall, which is
called capillary action. Rising damp occurs as a result of capillary suction of moisture from the
ground into porous masonry building materials such as stone, brick, earth and mortar. They may
cause unsightly deterioration of building exteriors and interiors as well as possible building structure
failures if left untreated. Their crystallization is in fact the cause of those phenomena of deterioration
that so often appear on surfaces: lack of cohesion, scaling, flaking and bulging. When the water
transporting the salts through porous materials evaporates, due, for example, to changing climatic
conditions, the solution becomes more concentrated. As soon as it becomes supersaturated, the
salts crystallize giving rise to both efflorescences on the surface and/or sub-efflorescences below the
surface layer. The impact of salt damp is often worse on external wall surfaces, especially those
exposed to direct sunlight, where evaporation is higher. This moisture then evaporates on or just
below the wall surface leaving the salt residues behind. There the salts are left behind and can often
be seen as a white efflorescence on the wall surface. When these salts grow as crystals within the
pores of the masonry they can disrupt even the strongest material, leading to fretting and crumbling
of the surface. These formations gradually contribute to building dilapidation and reduce the
building aesthetic values. The telltale signs of salt attack in a wall are: fretting mortar or stone or
brick, bubbling paint, crumbling plaster, and the presence of moisture on the surface of the wall. It
is very important to know the salt content of deteriorated surfaces both to understand the causes
of decay and plan conservation strategies. The nature of the salt provides us with information about its origin and therefore, indicates the possible conservation treatment to adopt. Sources of
salts can be the building materials themselves (sand, bricks, mortar), or external sources (soil,
materials used for conservation treatment, pollutants in the atmosphere, sea spray, de-icing salts
scattered on roads in winter, and products generated by the metabolism of micro- organisms). The
results of this research showed that almost all masonry contains soluble salts, principally sulphates,
nitrates, chlorides and carbonates of sodium, potassium, calcium, magnesium and ammonium and so, all
liquid water present in walls is more or less a diluted salt solution. Sources of these salts may be
natural or human induced. But, not all salts generate decay. This depends on their solubility,
hygroscopicity, mobility and the hydration level of their crystalline form.
