Infilling outdoor marble sculpture

Vanessa Wiggin <vanessa [at] artworksconservation__com> writes

>I have been asked to quote on the retreatment of an outdoor
>sculpture made of black and white marble.  The sculpture is subject
>to vibration due to its positioning and is heavily used by
>skateboarders.  This has resulted in extensive chipping to edges and
>corners.  The sculpture is located in a hot and sunny area.
>
>The losses were previously infilled with an epoxy resin and marble
>dust mixture.  While the result was aesthetically pleasing, the
>infills began to fail almost immediately.  Now two years later,
>almost all the fills have been lost or are pulling away from the
>stone.
>
>Can anyone suggest a more flexible fill material that will stand up
>to these conditions?  Discouraging all skateboarders is not
>currently on the agenda.

The original posting and subsequent responses have focussed on the
use of epoxy resin. The original posting states that this has
already failed after 2 years. Epoxy has a remarkable ability of
declaring itself unsuitable for outdoor use. Had this material not
failed so soon it would have continued to discolour and make its
presence increasingly obvious.

I am aware of the sculpture to which this treatment has been
applied, having made an inspection of it myself for the client prior
to the ill fated fills that are now failing. If the issue is that
fills are being dislodged through skateboarding or other external
forces then, simply stated, this does need to be put on the agenda.
The conservator must insist on this and seek professional support to
have the client understand that conservation is not an iron shroud
that can in any way counteract such adverse use. If we allow a
client to dictate such restrictions we are constantly forced to
adopt inappropriately hard technologies to counteract a lack of
responsibility to remove adverse impacts. This approach is akin to
waterproofing a floor because the client will not fix the roof.

But the main issue here is the use of epoxies in the outdoor
environment. They simply are unsuitable when exposed to UV. I use
epoxy quite extensively for outdoor repairs to stone and may have
even recommended it in my notes to the owner of this object but
certainly not as an exposed patching material.

The object consists of a black and white marble and each of these
can be readily matched using lime based repair materials, which
themselves will remain compatible with the marble and not impose
excessive strength. The two marbles present are reasonably
monochrome but I have matched quite complex colour variations using
pigmented lime based fills in the tradition of the scagliola
technique, where the various colours are blended and pigmented
throughout the entire depth of the fill.

The only remaining issue to resolve is gloss level, which of course
changes in time and separately for marble and fill. To achieve the
initial gloss a UV colour stable acrylic is incorporated at low
levels and does not act substantially as a binder. The surface is
then fine sanded to produce the desired gloss level. Having built a
scagliola fill permits such sanding without loosing surface colour.
The fill can be reworked in future years to re-match changing gloss.
Incorporating acrylic into lime mortars generally induces shrinkage
cracks but these tend not to overly weaken the fill. In fact in some
cases such cracks have been filled with contrasting colours to
produce very convincing veining.

I have recently inspected a fill in the described technique ten
years after application. It is a complex marble and hence much
easier to disguise but the results remain very acceptable with only
a margin of discolouration at the join. Repair to a Carrara marble
component on the same monument remains intact after ten years but
has discoloured due to its increased support for biological growth.
This repair is in the high moisture zone within a cornice and would
benefit from more regular cleaning.

In summary it is important for the conservator to lead the
discussion on protection and there are ways on this particular
object to modify it to some extent to reduce skateboard traffic.
Having worked with the artist's other works before his death I know
that modifications to the paving area around the marble forms would
have been seen as a necessary and acceptable compromise. Keep epoxy
away from light. Good luck,

Andrew Thorn
ARTCARE
614-1926-9326
Co-ordinator ICOM-CC Stone Working Group
Assistant Co-ordinator ICOM-CC Mural, Mosaic, Rock Art Working Group


                                  ***
                  Conservation DistList Instance 21:61
                  Distributed: Saturday, May 17, 2008
                       Message Id: cdl-21-61-007
                                  ***