Filling termite galleries

Daniel Cull <daniel.cull [at] themim__org> writes

>I am currently treating a wooden object from Papua New Guinea, that
>has damage from termites.
>
>I am looking for a method of filling the termite galleries in such a
>way that they will provide structural support for the now fragile
>overlying wooden surface. The fills need to be structural because
>the object will be on open exhibit, so more simple cosmetic repairs
>will not suffice.

I have worked on exactly this problem a few times where termites had
eaten a painted wooden building feature right through to the painted
surface in some places. Ignoring issues of retaining the surface
contour which doesn't seem to be an issue here, I approached this
problem using foamed epoxy. There is some literature within
conservation on this material but commercial formulations are no
longer available. While chatting with a former Ciba chemist he
spilled the beans on the foaming agent and so it is possible to
formulate this product to precise requirements much better by using
selected epoxy components.

The foaming agent is hydrogen functional siloxane, readily available
as the water repellent used in Wacker H and other hydrophobic ethyl
silicate based stone consolidants.

The commercial foamed product was formulated for a specific
industrial application that obviously did not list durability as one
of its key requirements. By taking as pure a Bisphenol A resin as
possible (that's almost impossible as epoxies use Bis E and others
to modify and flexibilize) and simply follow the correct
stoichiometric ratio, the foaming can be controlled by adding up to
1% siloxane. This will produce a 300% expansion and reduction in
strength to around 4MPa. Less siloxane reduces foam and increases
strength. Adding more than 1% is more like making pop corn but it
can allow further strength reductions. Epoxy strength is isotropic
so achieving compressive and tensile strength is simply a matter of
knowing which matters more. Flexural strength is not great which
only becomes a factor when working on long thin architectural
features such as skirtings and architraves. Generally bis A with
hardener will be too thin to foam so it needs to be thickened with
fumed silica and this can also include glass or ceramic spheres at
the risk of reducing penetration into smaller voids. The spheres
give a less flexible resin which is closer to the brittle nature of
the termite carton you have.

If unfamiliar with the foaming action of epoxy, this is a very
gentle action that continues to increase in volume over about 60
minutes at 20-25 deg. C. You can use solvents to slow it down and I
am happy to discuss the details of this direct. The great advantage
of the foaming action is that it delivers the resin through the
tunnels which are long and continuous. Having recently worked with
termite tunnels from Papua I know you have generous dimensions to
pass the resin through but it can be made to naturally infiltrate
0.1 mm voids without difficulty or force, other than its inherent
foaming action. You may have limited access to the tunnels as the
subterranean termites from this region do not emerge from the
structure willingly and so do not create great numbers of surface
openings.

Epoxies have earned themselves a bad reputation but alas this is all
down to poor use and decision making. This is one of at least two
applications where I believe it stands out as an ideal candidate.

If you want to know more about how to formulate this resin I am
happy to correspond as I am currently putting together some notes on
its other positive application. If you want to know more on PNG
termites I can put you in touch with the expert on that topic too.

You will also need to consider consolidation of the material which
will be more termite carton than wood. It will be extremely brittle
but consolidation with B72 or similar can improve this condition and
serves to isolate the carton from the epoxy. Foamed epoxy is
amenable to removal with gentle heat but you will need the termites
to go in and do that for you.

Andrew Thorn


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                  Conservation DistList Instance 23:19
                 Distributed: Sunday, November 29, 2009
                       Message Id: cdl-23-19-005
                                  ***