pore volume completely) with a solution that contains 10% Butvar B98 by
volume. With a relative density of cell-wall substance of 1.5 and a relative
density of the bound water of 1.014 (note that 12% is less than the fiber
saturation point in wood so that no free water will be present), the frac-
tional pore volume can be calculated as: V 512 0.5 (1/1.5 1 0.12/1.014) 5
0.61 (Kellogg 1989). Butvar B98 has a relative density of 1.1. Of the total
pore volume, 10%, or 0.061, is occupied by resin. Since a relative density of
1.1 corresponds to a density of 1100 kg m^23 , this converts to 67 kg m^23 ;
and when this is added to the wood density of 500 kg m^23 , it represents
an increase, or resin loading, of 13.4%. The relative density of 0.5 corre-
sponds to the high end of the range for typical softwoods in their original
state. As the wood deteriorates, the relative density decreases and the
porosity increases, making higher loading possible. In impregnation of
wood with monomers, with subsequent curing in situ, much higher load-
ing is possible—even when the polymer shrinkage during curing and the
loss of monomer due to evaporation are taken into account (Simunkovà,
Smejkalovà, and Zelinger 1983; Schneider 1994).Methods of application
The most simple and straightforward way to apply consolidant is by
brushing. In most cases it is quite difficult to get substantial penetration
bybrushing, but an adequate treatment can result ifonly the surface lay-
ers need to be strengthened. For catalyzed systems (i.e., thermosetting
resins or resins polymerized in situ), brushing is probably the least effective
method because the treatment is limited to a single application. Consolidant
solutions, however, offer a somewhat better prospect, since it is possible to
make more than one application. Grattan found that better results could
be obtained by applying many coats of consolidant solution of low resin
concentration, whereas solutions of high concentration can lead to the
early development of an objectionable gloss on the artifact surface
(Grattan 1980). Barclay was able to use a brush treatment of 5% solution
of Butvar B98 in ethanol on portions of an English fire engine with good
results (Barclay 1981).
To improve on the penetration achieved by brushing, some form
of treatment that keeps the object in contact with consolidant solution over
a period of time without allowing any intermediate drying can be very
effective. This procedure can take the form of soaking in consolidant solu-
tion, as with two canoes treated with PVA in toluene in Japan (Chemical
Section and Section for Repairing Technique 1968). However, considerations
of cost, safety, and eventual disposal problems may speak against the use of
the large quantities of solution that would be required for large objects. The
alternative approach is to use a continuous or intermittent recirculating
spray system within an enclosed space. A California Native American
dugout canoe was treated in this manner. The treatment used a 13% solu-
tion (weight basis) ofAYAT, a PVA, in methanol within a temporary enclo-
sure, and achieved complete penetration of the wood (Schniewind and
Kronkright 1984). A somewhat different approach was used by Nakhla
(1986): consolidant solution was applied in drops onto the objects being
treated. As long as the rate of application is consistent enough to keep
the object wet with solution, this can also be a very effective method.
Consolidant may also be injected selectively (Wermuth 1990).94 Schniewind