Building Design and Construction Handbook - Merritt - Ventech!

4.50 SECTION FOUR
pumped in under pressure against the back pressure of the compressed air in the
wood. When the pressure is released, the air in the wood expands and forces out
excess preservative, leaving only a coating of preservative on the cell walls.
Retentions of preservative depend on the application. For teredo-infestation, fullcell
creosote treatment to refusal may be specified, ranging from 16 to 20 lb per
cubic foot of wood. For ordinary decay conditions and resistance to termites and
other destroyers of a similar nature, the empty-cell method may be employed with
retentions in the vicinity of 6 to 8 lb of creosote per cubic foot of wood. Salt
retentions generally range in the vicinity of 1 1 ⁄2 to 3 lb of dry salt retained per
cubic food of wood.
Solvent-soluble organic materials, such as pentachlorphenol, are commonly employed
for the treatment of sash and door parts to impart greater resistance to decay.
This is commonly done by simply dipping the parts in the solution and then allowing
them to dry. As the organic solvent evaporates, it leaves the water-insoluble
preservative behind in the wood.
These organic materials are also employed for general preservative treatment,
including fence posts and structural lumber. The water-soluble salts and solventsoluble
organic architects leave the wood clean and paintable. Creosote in general
cannot be painted over, although partial success can be achieved with top-quality
aluminum-flake pigment paints.
Treatment against fire consists generally of applying salts containing ammonium
and phosphates, of which monoammonium phosphate and diammonium phosphate
are widely employed. At retentions of 3 to 5 lb of dry salt per cubic foot, the wood
does not support its own combustion, and the afterglow when fire is removed is
short. A variety of surface treatments is also available, most of which depend on
the formation of a blanket of inert-gas bubbles over the surface of the wood in the
presence of flame or other sources of heat. The blanket of bubbles insulates the
wood beneath and retards combustion.
See also Art. 10.6.
4.37 GLUES AND ADHESIVES FOR WOOD
A variety of adhesives is now available for use with wood, depending on the final
application. The older adhesives include animal glue, casein glue, and a variety of
vegetable glues, of which soybean is today the most important. Animal glues provide
strong, tough, easily made joints, which, however, are not moisture-resistant.
Casein mixed with cold water, when properly formulated, provides highly moistureresistant
glue joints, although they cannot be called waterproof. The vegetable glues
have good dry strength but are not moisture-resistant.
The principal high-strength glues today are synthetic resins, of which phenol
formaldehyde, urea formaldehyde, resorcinol formaldehyde, melamine formaldehyde,
and epoxy are the most important. Phenol, resorcinol, and melamine provide
glue joints that are completely waterproof and will not separate when properly made
even on boiling. Urea formaldehyde provides a glue joint of high moisture resistance,
although not quite so good as the other three. Phenol and melamine require
application of heat, as well as pressure, to cure the adhesive. Urea and resorcinol,
however, can be formulated to be mixed with water at ordinary temperatures and
hardened without application of heat above room temperature. Waterproof plywood
is commonly made in hot-plate presses with phenolic or melamine adhesive. Re-