THE SOLUBLE SALTS IN THE BUILT HERITAGE

Transcription

1 THE SOLUBLE SALTS IN THE BUILT HERITAGE Stone materials and conservation of the built heritage The soluble salts _ BR /1 Principal ions of the harmful soluble salts: Cations Na + (sodium) K + (potassium) Ca ++ (calcium) Mg ++ (magnesium) NH 4+ (ammonium) Anions CO -- 3 (carbonate) HCO 3- (hydrogencarbonate) SO -- 4 (sulphate) NO 3- (nitrate) Cl - (chloride) C 2 O 4 (oxalate) Stone materials and conservation of the built heritage The soluble salts _ BR /2 Principal soluble salts in building stones (in CH): English French halite " NaCl Chlorides sylvite sylvine KCl niter salpêtre, nitre KNO 3 Nitrates nitronatrite ", nitratine NaNO 3 ammonium nitrate nitrate d'ammonium NH 4 NO 3 (ph<7) thenardite thénardite Na 2 SO 4 mirabilite " Na 2 SO 4.10H 2 O Sulphates gypsum gypse CaSO 4.2H 2 O epsomite " MgSO 4.7H 2 O arcanite " K 2 SO 4 calcite " CaCO 3 (ph>7) Carbonates natron " Na 2 CO 3.10H 2 O (ph>7) thermonatrite " Na 2 CO 3.H 2 O (ph>7) trona " Na 3 H(CO 3 ) 2.2H 2 O (ph>7) Oxalates weddellite " Ca(C 2 O 4 ) 2(H 2 O) whewellite " Ca(C 2 O 4 ) (H 2 O) Complex salts ettringite " Ca 6 Al 2 (SO 4 ) 3 (OH) 12.26H 2 O darapskite " Na 3 (SO 4 )(NO 3 ) H 2 O Stone materials and conservation of the built heritage The soluble salts _ BR /3 1

2 Origin of the soluble salts: Natural origins: Sea water (all ions NO 3-, NH 4+ ) Groundwaters (all ions ) Fresh waters (all ions) Organic origin (NO 3-, NH 4+, oxalates C 2 O 2-4, HC 2 O 4- ) Natural building materials: ex. : sandstone of Berne ( 0.1% Ca 2+ et SO 2-4 ) Stone materials and conservation of the built heritage The soluble salts _ BR /4 Origin of the soluble salts: Restoration materials: - cleaning products (formic acid, ammonium carbonate) - conservation products (oxalates) - additives of the conservation products (ammonia) Air pollution (sulphate, nitrogen oxides, etc.) - dry deposition - wet deposition Stone materials and conservation of the built heritage The soluble salts _ BR /5 Origin of the soluble salts: De-icing salts - NaCl, CaCl 2, Alkali building materials - Cement (Na +, K +, SO 2-4, ) - Soluble glasses (Wasserglas) (K + ± Na + ± Li + ) - Trass (Na +, K +, Mg 2+, ) Fireproof materials - Boron salts - Wasserglass Stone materials and conservation of the built heritage The soluble salts _ BR /6 2

3 The crystallization problem Stone materials and conservation of the built heritage The soluble salts _ BR /7 Fribourg, Stone materials and conservation of the built heritage The soluble salts _ BR /8 Nancy, Black crust of gypsum on the Euville limestone Stone materials and conservation of the built heritage The soluble salts _ BR /9 3

4 From: Arnold, A.; Zehnder, K. (1991): Monitoring wall paintings affected by soluble salts.- The Conservation of Wall Paintings. Proc. Symp. Courtauld Inst. Art & Getty Conservation Inst., London, July 13-16, 1987, The Getty Conservation Institute. Stone materials and conservation of the built heritage The soluble salts _ BR /10 Nancy, rampart, (photo: C. Bläuer) Stone materials and conservation of the built heritage The soluble salts _ BR /11 Paint layer on a ceramic with halite (NaCl) efflorescences (Laborexperiment) Photo Konrad Zehnder Stone materials and conservation of the built heritage The soluble salts _ BR /12 4

5 aus: Arnold, A.; Zehnder, K. (1991): Monitoring wall paintings affected by soluble salts.- The Conservation of Wall Paintings. Proc. Symp. Courtauld Inst. Art & Getty Conservation Inst., London, July 13-16, 1987, The Getty Conservation Institute. Stone materials and conservation of the built heritage The soluble salts _ BR /13 Photos: Konrad Zehnder Nitronatrite (NaNO 3 ) in ceramic (lab. experiment) Stone materials and conservation of the built heritage The soluble salts _ BR /14 Condensation (internal & nord) Origin of salts and water in buildings infiltrations mortars, concrete stones ground déjections liquid water supplies rain de-icing salts treatments smog, dust fertilizer, déjections Stone materials and conservation of the built heritage The soluble salts _ BR /15 5

6 Evolution of water and salts in case of slow drying liquid transfers little or no wind little or no insolation => efflorescences, patinas, crusts => not very harmful Stone materials and conservation of the built heritage The soluble salts _ BR /16 Evolution of water and salts in case of fast drying vapour transfers liquid transfers wind intense insolation => scaling, blistering, granular disintegration, differential weathering => very harmful Stone materials and conservation of the built heritage The soluble salts _ BR /17 The hygroscopicity (or deliquescence) problem Deliquescence humidity: the relative humidity above which a material absorbes humidity from the air and dissolves Stone materials and conservation of the built heritage The soluble salts _ BR /18 6

7 Fribourg, Notre-Dame basilica, Stone materials and conservation of the built heritage The soluble salts _ BR /19 Kaysersberg castel, Alsace, France, Vincent COURCELEAUD ( Stone materials and conservation of the built heritage The soluble salts _ BR /20 Deliquescence humidity & temperature Steiger, M. Stone materials and conservation of the built heritage The soluble salts _ BR /21 7

8 Stone materials and conservation of the built heritage The soluble salts _ BR /22 8