Environmental Engineering Reference
In-Depth Information
Salt
Possible origins
Antarcticite, CaCl
2
.6H
2
O
De-icing salt
Arcanite, K
2
SO
4
Degradation of potassium-containing stained glass
window, potassium silicate treatments (waterglass)
Calcite, CaCO
3
Leaching of limestone, leaching of lime or cement
mortars, reaction between salts*
Ettringite,
K
2
Ca
6
Al
2
(SO
4
)
3
(OH)
12
.26H
2
O
Cements, reaction between cement and gypsum-containing
materials
Gypsum, CaSO
4
.2H
2
O
Atmospheric pollution, gypsum plasters, certain rocks,
cements, cement-containing mortars, sea spray
Halite, NaCl
Sea water, sea spray, de-icing salts, conservation salts
Kieserite, MgSO
4
.H
2
O
Epsomite, MgSO
4
.7H
2
O
All rocks or mortars containing Mg; interaction
atmospheric pollution/dolomitic rocks
Natron, Na
2
CO
3
.10H2O
Cements, mortars, washing powders, chemical cleaning
products, mortars prepared with sea water
Sodium nitrate, NaNO
3
Decomposed organic matter, soil
Potassium nitrate, KNO
3
Decomposed organic matter, soil, fertilizers
Nitrocalcite, Ca(NO
3
)
2
.4H
2
O
Atmospheric pollution, decomposed organic matter, soil
Sylvite, KCl
Soil
Thaumasite,
Ca3Si(CO
3
)(OH)
6
(SO
4
).12H
2
O
Cements, reaction cements/gypsum plaster
Thenardite, Na
2
SO
4
Mirabilite, Na
2
SO
4
.10H
2
O
Cements, cement mortars, washing powders, bricks
Table 8.5.
Salts that can be found on monuments and their origins
[ASH 89, BER 95, BER 96]
8.3.2.2
. Properties of salts
The chemical and physical properties of salts determine their behavior and, to a
certain extent, their harmfulness. Some salts such as natron have an alkaline pH and
are thus able to the attack silicate minerals in granite [BER 95], or sensitive
pigments in polychrome items. Such chemical attacks are quite rare though. Physical
properties are far more important in determining the nature and distribution of salt-
related degradation patterns.
