Adhesive for stone

Olaf Pung posted a query regarding reassembly of a small Egyptian
limestone statuette which had been dowelled.

Removal of the dowels is probably necessary, as Olaf suggested.
Sometimes they are loose and can be easily removed. Some will have
corroded and become attached to the stone and may need very careful
mechanical cleaning to enable them to be detached.

The stone may need consolidation before any attempt is made to join
the fragments. For this we have found Paraloid (Acryloid in the USA)
B72 dissolved in acetone to be simple and effective. Concentrations
vary according to the porosity and fragility of the stone, between
5% - 25% weight/vol. The solution is applied from a pipette and
allowed to flow on to the surface as it is absorbed. The freshly
consolidated stone is then at its most fragile and must not be
handled until the solvent has evaporated and the resin is hard
throughout.

A more viscous solution of the same copolymer will act as an
excellent adhesive. Alternatively an acrylic copolymer soluble in a
different solvent may be preferred so that joins can be taken down
in future without softening the consolidant in the body of the
stone.

On no account use an aqueous solution on dry limestone unless you
are certain that the stone does not have a problem with salts and
does not contain iron compounds or the organic substances which many
Egyptian limestones do. Bringing moisture in contact with the stone
(by using a colloidal dispersion, an emulsion or a water-based
adhesive) can cause efflorescence of salt-crystals, yellow or orange
staining, solution of fragile areas of limestone and other problems.
Water can be used with limestones of course (for example some
limestones require desalination by immersion in water) but they must
be very carefully tested first and such treatments should not be
undertaken by the inexperienced without supervision. Good luck,

Helena Jaeschke
Archaeological Conservator

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                  Conservation DistList Instance 11:74
                   Distributed: Friday, March 6, 1998
                       Message Id: cdl-11-74-004
                                  ***