Wood-based panel products are often found among the supports for paint-
ings of the twentieth century. In particular, these include fiberboard, hard-
board, particleboard (also referred to as pressboard and chipboard), and
plywood. All of these consist of wood elements and some type of binder
oradhesive. A survey of wood-based composite materials used in twentieth-
century furniture and the problems they represent have been discussed
by Klim (1990).
Since the adhesives used may not be moisture resistant and
because extreme moisture conditions can create significant internal stresses
in the material, there is always the danger of failure of the adhesive bonds
and subsequent disintegration of the panel material. Particleboard is par-
ticularly subject to recovery of the large deformations of the particles
incurred during the original pressing process, when it is exposed to high
relative humidity. This is known as springback, a condition that may result
in thickness swelling of 20% or more, as well as in a disruption and rough-
ening of the surface (Moslemi 1974). For this reason, particleboard has to
be considered one of the most unstable painting supports. Prolonged con-
ditions of high moisture may lead to complete disintegration; thus fungal
decay is not likely to be a problem with particleboard, because it will dis-
integrate at moisture contents sufficient to support decay—before the
decayitselfcan do much damage.
In plywood, moisture problems can lead to surface checking,
which could easily disrupt thin paint layers (Minor 1993), or to delamina-
tion (Williams and Creager 1993). Neither of these problems lends itself to
being solved by a bulk treatment such as impregnation. There are no readily
apparent methods of dealing with surface checks, especially if they are
numerous and the conditions leading to the checking are likely to be per-
sistent (Minor 1993). Williams and Creager have outlined some approaches
to dealing with delamination, ranging from local repairs to a partial trans-
fer (i.e., discarding all but the face ply bearing the image and attaching it
to an alternate support) (Williams and Creager 1993). The permeability
of these new wood-based panel materials additionally differs from that of
solid wood. In plywood, the lathe checks can serve as pathways for fluid
transport along the grain within a ply, so that the wood is very permeable
from its edges. Because of the adhesive layers, however, permeability
through the thickness is quite low (O’Halloran 1989a). This factor could
make plywood more difficult to treat if there is deterioration of biological
origin that does not involve delamination. Particleboard and fiberboard are
more permeable than solid wood because they contain interconnected
void spaces (O’Halloran 1989b). As in the case of solid wood, whatever
type of deterioration takes place will increase permeability, a factor that
serves to facilitate treatment by impregnation.Acryloid B72, Rohm and Haas Company, Independence Mall West, Philadelphia, PA19105.
AYAT,Union Carbide Corporation, Old Ridgebury Road, Danbury, CT 06817.
Butvar B90 and B98,Monsanto Plastics and Resin Co., 800 N. Lindbergh Blvd., St. Louis, MO 63166.Anderson, A. B., E. L. Ellwood, E. Zavarin, and R. W. Erickson
References 1960 Seasoning stain of redwood lumber. Forest Products Journal10(4):212–18.
Materials and Suppliers
Special Problems with
Wood-Based Panel
Products
C W P 103