Colloidal silica

Elsa Bourguignon <ebourguignon [at] getty__edu> writes

>I am interested in hearing from conservators who have experience of
>using colloidal silica (brand names Syton, Ludox...) in stone
>conservation, both as a binder in a grout and as a consolidant for
>surface applications.

The material is used in Germany since the late 80s. It was modified
by Thomas Lehmkuhl; in his diploma thesis (Koeln, 1990), he added
fumed silica and used a kind of "dispersive mixer" to get the
mixture homogeneous. The grouting had improved flow properties.

During the years, German conservators had bad experience with these
groutings and fillings: They discolored after a few years. As far as
I know, the cause of this phenomena in still unknown.

Recently, German conservators are more and more shifting to a
alkoxysilane named Funcosil 500 STE (manufactured by Remmers,
Loningen, Germany). It is delivered with a siliceous filler. In my
experience, the material was easy to handle and showed perfect flow
properties. The mass had sufficient hardness after curing. It is
compatible with other alkoxysilanes. In contrary to SYTON, the
alkoxysilane does not contain water, there is no danger of salt
efflorescence.

There are lots of papers in German on this subject. If its useful to
you, I can give you the references.

Olaf Pung
Stone conservator
Berlin


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                  Conservation DistList Instance 15:55
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