Consolidation of sepiolite-rich armorial panel

I am seeking advice on how to consolidate a dark grey fine-grained
sandstone with distinctly pale and brittle sub-surface laminae.  XRD
analysis has identified the latter to be a sepiolite-rich sediment.
Sepiolite is an expansive clay (through hydration) and this appears
to have led to the lifting and sub-surface detachment of the surface
in the past.

However, previous consolidation attempts through injection of 10%
(w/v) Paraloid B72 dissolved in acetone have resulted in further
expansion of these layers and distortion of the surface.
Subsequently, I am looking for a reversible adhesive mixed with a
solvent that does not cause sepiolite to swell and which can be
mixed with micro-balloons or similar inert material to form a
filler, allowing us to re-adhere the surface in its correct shape.

The paper "The role of sepiolite-palygorskite in the decay of
ancient Egyptian limestone sculptures" by Rodrigues-Navarro et al
discusses a similar problem and offers preventive conservation
suggestions.  However, has anyone dealt with the remedial
consolidation of such stones?  Any practical suggestions would be
gratefully received.

The medieval armorial panel has been stored indoors and, together
with a collection of many exquisitely carved stones from the ruined
13th century cathedral, will form part of a new visitor display
inside the remaining towers of Elgin Cathedral.

Christa Gerdwilker
Stone Conservator
Historic Scotland


                                  ***
                  Conservation DistList Instance 29:19
                Distributed: Sunday, September 27, 2015
                       Message Id: cdl-29-19-014
                                  ***