Connecting to Collections Care

Hi all –

Has anyone had experience with removing efflorescence  from granite and if so, would you be willing to share advice and/or cut sheets of the products used? We're in the process of finalizing an historic iron gate + granite archway restoration and have received bids from two contractors to handle the granite component but their recommended treatments are slightly different.  Hoping to check against another source.  Also curious if anyone has chosen to seal a cleaned granite surface and if that was successful as a long-term preventative. Thanks.

Deb Wold

Senior Collections Manager

Longyear Museum

Chestnut Hill, Massachusetts 

T: 617.278.9000 x 320

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As Lorraine Schnabel explained, the source of the water ingress which has resulted in the efflorescence needs to be tackled. 

In Egypt we found the problem is often salt-rich groundwater, exacerbated by hygroscopic salts and clay particles in the salty soil at ground level. Previous attempts to wash off the efflorescence, had resulted in repeated wetting of the granite, followed by evaporation which drew up more salty groundwater and resulted in more efflorescence. This also led to the breakdown of the structure of granite, with large crystals spalling off the surface.    In one instance the granite had been placed on a concrete plinth to raise it off the ground, but without any impermeable barrier. Groundwater rose through the concrete and the resulting damage was even more rapid and severe because of the presence of alkaline compounds leached from the cement. The only remedy was to keep the surface dry (gently brushing off the efflorescence) and arrange for a barrier layer between the granite and the source of the groundwater. Ideally this should be between the granite and any plinth, especially if it is made with cementitious material.

As long as moisture can enter the granite from one surface, sealing all the other surfaces is likely to lead to accelerated deterioration. Granite is porous, brittle and inherently unstable but its size and mass mean we think of it as strong and robust.

Sorry not to have more simple, positive solutions!

Best wishes

Helena

Helena Jaeschke

Conservation Development Officer

South West Museum Development

https://southwestmuseums.org.uk/