Problems with epoxy in stone conservation

I used ground limestone as a filler in Araldite AY103 in order to
fix stones with stainless steel dowels. This caused cracks in the
stone, parallel to the steel rods. Here are some more details:

    Object: posts of a fence around a grave monument. Measures:
        20/20/140 cm
    Steel rod: diameter 1cm
    Stone material: oolithic limestone (oospatit)
    Origin: Savonnieres, Lorraine, France (west of Nancy)
    Geologic classification: Jura, Portlandium
    85-90% CaCO3, 0.3% Goethit (Fe-oxide-hydroxide), gypsum.
    Porosity: 20-25% (stone is very "soft")
    The same stone, ground, was used to fill the epoxy.

A geologist, engaged in the treatment of Savonnieres-limestone, told
me about difficulties in treating this stone with PMMA. He thinks
that organic components in the stone are responsible for this.

Petr Kotlik, Czech Republic, who has experiences with "artificial
sandstone" (epoxy, quartz sand), reported of epoxy filled with much
sand destroyed by swelling in water after hardening. I tried this,
too, but found that my epoxy-mass had no porosity and didn't take
any water.

At last I suppose that a chemical reaction between the epoxy
components and the CaCO3 caused the expansion; maybe heat caused
expansion of the steel? I wonder if anybody has an idea.

Olaf Pung,
Stone conservator in education at Fachhochschule Hildesheim, Germany

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                  Conservation DistList Instance 11:72
                Distributed: Tuesday, February 24, 1998
                       Message Id: cdl-11-72-014
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