Series editors' preface - Wood Tools

Hammer veneering with animal/hide glue is
another example, but in this case the veneer
should be flexible enough to be fitted closely
to the carcase as the glue cools and gels.
Cyanoacrylates, which cure very rapidly, may
also function as self clamping adhesives.
Distribution of clamping pressure is an
important consideration in achieving optimum
results. If a wide flat component is to be
clamped, the clamps must be spaced closely
enough together that the adherends cannot
bow away from each other between pressure
points. A rigid material shaped to the adherend
surface, known as a caul, can be employed to
distribute clamping pressure evenly on curved
surfaces or components (Figure 10.4). Cauls
can be as simple as a flat board or as complex
as the inversely shaped and metal-covered
heatable cauls used traditionally to veneer
mouldings and complex surfaces. Some
conservators make cauls for laying/flattening
veneer from 18 mm ( 3 ⁄4 in) chipboard lined with
lead, zinc or brass sheet. Brass sheet (e.g. 16
SWG) may be screwed and countersunk into
the board and can be warmed on a hot plate
before use. It may be helpful to line a shaped
caul with bandsawn veneers of varying thickness
in order to facilitate adjustment of the final
shape of the caul. Such linings may also be
made from balsa or fibreboard depending on
the desired compressibility. All these linings
may be attached with a contact adhesive and
faced with foam or Melinex/Mylar. Hot sand
bags may also be used to veneer complex
surfaces, functioning as self-shaping cauls.
Small pieces of acrylic or polycarbonate sheet
make excellent cauls for regluing small parts
and veneers because the squeeze out of the
glue can be observed through them, indicating
the degree of conformity to the surfaces, and
because they shear away cleanly from the
surfaces after the glue is hard. They can also
be pre-warmed by immersing them in hot
water. Cauls have the additional important
purpose of protecting show surfaces from
damage by clamps. Cauls should be inspected
before use to ensure they are free from old
dried glue and the like, which would damage
an original surface. Cauls that do not cover the
entire surface may need to be softer than the
surface of the object and have rounded edges
to avoid denting the surface that is being
veneered.
Principles of conserving and repairing wooden furniture 445
(a)
(b)
Figure 10.4 Cramping curved surfaces
(a) Cramping a curved chair back. Scrap wood is
shaped to fit the curved crest rail. Thin foam can be
used as softening to prevent damage. Supports can be
screwed to the shaped cramping block to prevent lateral
movement when pressure is applied
(b) Cramping a semi-circular table top
The clamping pressure required will depend
on the nature and porosity of the adherend, the
viscosity and gap filling ability of the adhesive
and the density of the wood. More pressure
may be required for non-porous substrates,
viscous adhesives and high density woods.
Heavy cramping pressure is not necessary for a
well made joint and the conservator should aim