|Color code :||
|Translations :||NC, NC, croûte, NC, NC|
|Definition :||Generally coherent accumulation of materials on the surface. A crust may include exogenic deposits in combination with materials derived from the stone.
A crust is frequently dark coloured (black crust) but light colours can also be found. Crusts may have an homogeneous thickness, and thus replicate the stone surface, or have irregular thickness and disturb the reading of the stone surface details.
|Relationship with the substrate :||A crust may be weakly or strongly bonded to the substrate.
Often, crusts detached from the substrate include stone material.
|Equivalent terms to be found in other glossaries :||NA|
|Other orthograph :||NA|
|Sub-type(s) :||- Black crust : Kind of crust developing generally on areas
protected against direct rainfall or water runoff in urban environment.
Black crusts usually adhere firmly to the substrate.
They are composed mainly of particles from the atmosphere,
trapped into a gypsum (CaSO4.2H2O). matrix.
- Salt crust : Crust composed of soluble salts, which develop in the presence of high salt levels, and form from wetting and drying cycles.
|Not to be confused with :||- Encrustation, witch is also a coherent layer, but is always adherent to the subsrate. The term encrustation is preferred to crust when the accumulation clearly results from water infiltration followed by precipitation.
- Alga : Algae often have a dark colour during the dry season and may be confused with black crusts. Oppositely to black crusts, algae do not adhere to the substrate, and are usally located, in outdoors situations, in area exposed to direct rain impact, or on water pathways. These two characteristics differenciate algae from black crusts.
- Patina : Black iron rich patinas, which develop usually as a thin layer enriched in iron/clay minerals on iron containing sandstones, and are located on all exposed parts of the building/sculpture, not only on parts sheltered from the rain impact.
|Other remarks :||NC|
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