Adhesive for exterior woodwork

Rian Deurenberg <rdeurenberg [at] philamuseum__org> writes

>I am investigating adhesives to be used in the treatment of four
>exterior ionic capitals (attr. to Bernard and Jugiez, ca. 1765),
>carved in vertical grained southern yellow pine. ...

I've had very good success using ConServ flexible epoxy (ConServ
Flexible Epoxy Patch 200). It is more of a filler than an actual
adhesive although bonding properties are excellent.  I've got fills
in place outside in exposed conditions for more than ten years now
with no sign of failure--no separation at the interface or
degradation of the material itself. Workability is decent but not
what I would call easy although I have worked molded surfaces on it.
It is very slow setting (several days depending on temp and RH).
Gap-filling qualities are excellent as you might expect being a
filler.  The material comes with both fumed silica and also a
cellulose-based material for bulking it up which can be done more
less according to application. The cellulose helps with
"carvability".   I probably don't need to warn you about fumed
silica but will anyhow--nasty stuff--*extremely* fine--I sometimes
refer to it as "weaponized" silica because it becomes air-borne so
readily. I use a respirator when mixing it in.

It takes paint very well, I have had no problems with paint
adherance using either oil-based or acrylic latex.  The material is
intended to be used with a flexible epoxy consolidant and the
instructions state that any fill applications should be preceded by
treatment with their consolidant(ConServ Flexible Epoxy Consolidant
100. However, if no consolidation is required, I've found that
applying the filler in the mixed, liquid state (before bulking up)
to the surfaces provides a good bond by allowing the material "wet
in" when the filler is applied. This saves mixing up two different
materials as the consolidant epoxy is a different formulation than
the filler. As far as reversibility is concerned--as with any
epoxy--it is limited although being flexible it would be easier to
dig out than the harder epoxies.  Speaking of which, I have used
other epoxies bulked up with fumed silica as fillers notably Abatron
and West System and have found them to be poor filler materials with
separations typically occurring at the interface rather quickly,
allowing water infiltration than then leads to more problems
developing in a predictable fashion. I have also found the same to
be true of polyester resin based materials (body filler) when used
outside.

Robert Self
Architectural Conservator
Monticello
Charlottesville, VA 22902
434-984-9851


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                  Conservation DistList Instance 16:75
                  Distributed: Thursday, May 29, 2003
                       Message Id: cdl-16-75-005
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