Fiberglass sculpture

Barbara Appelbaum <aandh<-at->mindspring<.>com> writes

>I am working on a resin/fiberglass sculpture.  The basic structure
>is two hollow spheres, each about 1-2 feet long, that were attached
>at an area about two inches in diameter.  It broke at the neck,
>leaving only small areas of contact where an adhesive could go.  In
>order to make the repair strong, we have been thinking about filling
>one of the spheres so that we could establish something solid to use
>to increase the area of adhesive contact.  Does anyone know of an
>injectable foam with decent aging properties?

I have been foaming epoxies for conservation use for many years and
am compiling data on the properties, especially in relation to aging
and the rheology of foaming levels. I agree with Robert that foamed
epoxy alone will be heavy, particularly if you use the commercial
formulation. In industry these are referred to as blown resins and
one option, when working in a contained space is to blow the resin
even more. This produces a weak structure and I feel is not the
right approach.  I would also do what Robert suggests and reduce the
placement using balloons or similar. I have also used prophylactics
in one situation where I needed to inject and hold the resin in a
particular point inside a wall cavity.

I just want to add that tailor making your own system is infinitely
better than relying on commerce. They generally formulate a 3%
foaming addition that gives 300% +/- expansion and reduces the
strength from approximately 20 to 4 MPa. In conservation you may
want to have a strong ring at 10MPa, spaced with overblown resin
filling, etc. The critical thing is that by formulating and
controlling the expansion you can put the tensile strength where you
need 1it and fill with lighter weight material elsewhere.

I would also look at alternative weight reducers. The commercial
product relies on gas generation and the use of glass
micro-balloons. For much of my work, where I want a more flexible
foamed resin, I omit the micro-balloons and thicken entirely with
fumed silica. I also incorporate fire suppressants where necessary,
in roof spaces etc, where the raw epoxy contributes to the
combustible fuel load. You might consider larger air spacers such as
ping pong balls or polystyrene balls etc. If they deteriorate you
are left with a perfectly stable air void with no reduction in
strength.

Having read your brief discussion however I feel there are more
significant structural issues that need to be addressed by means
other than foaming resins.

If you want more information on a controlled flexible system post a
reply here and I can correspond through email.

Andrew Thorn
ARTCARE


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                  Conservation DistList Instance 27:19
                Distributed: Wednesday, October 30, 2013
                       Message Id: cdl-27-19-002
                                  ***