BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

20 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 207
from 1 to 3 years to the life of wood placed
in the ground. However, exposure to the weather
or contact with soil or water will quickly leach
out a waterborne preservative applied by brush.
Such superficial treatments are most successful
in those timbers that have little resistance to
impregnation.
Other nonpressure methods are used with considerable
success, depending on the preservative,
the permeability of the timber, and the use of the
treated material. Wood can be impregnated as
successfully with the hot-and-cold-bath processes,
cold soaking and steeping, or some of the other
nonpressure methods, as with the pressure processes,
if the wood has a low resistance to treatment.
The value of preservative treatment depends
on the retention and penetration achieved
and not on the process used. But, if the wood
resists treatment, one of the pressure processes
will give better results for they have the advantage
of giving more uniform and dependable
treatment.
Many preservatives are used with good results.
Coal-tar creosote, the most important and most
extensively used, is considered the best preservative
for general outdoor use in structural timbers
and for marine use, but it is not adapted for material
that will be painted or where its odor is
objectionable. Where creosote is unsuitable,
pentachlorophenol and copper napthenate in
petroleum oil solutions are substituted extensively.
Pentachlorophenol in mineral spirits or other
volatile light-colored solvents is gellerally used
for window sash, millwork, interior trim, and
other material requiring clean, paintable surfaces.
Copper naphenate and pentachlorophenol in
various grades of petroleum oil are also used extensively
for the commericial treatment of lumber,
posts, and poles. Both preservatives provide a
high degree of protection against decay and termites,
but are less effective than creosote against
marine borers.
Paintability of wood is affected by the type of
petroleum oil used in the treating solutions;
usually, the heavier oils of low volatility give the
best preservative service but are most likely to
interfere with painting. The use of “bloom” preservatives,
such as ester gum, is required when
pentachlorophenol solutions are used with volatile
solvents; bloom preservatives prevent the formation
of crystals on the surface of the wood after
treatment.
In the United States, several water-repellent
preservatives are sold under various trade names
for the treatment of millwork and other interior
work. Containing either pentachlorophenol or
copper napthenate, they are valued for retarding
moisture changes in wood and for protection
against decay and insects.
Wood preservatives used in water solution are
also effective against insects and decay, but are
acceptable only n-here the wood will not come in
contact with the ground or water. Preservatives
of this type include zinc chloride, chromated zinc
chloride, Tanalith (Wolman Salts), acid copper
chromate (Celcure), and chromated zinc arsenate
(Greensalt or Erdalith). These preservatives
leave the surfaces clean, paintable, and free from
any objectionable odor, but, in general, they are
more subject to leaching when exposed to the elements
than the oilborne preservatives. However.
they are generally more acceptable for inside use
than creosote and other preservatives in heavy
petroleum oils, and give long service when not
exposed to the elements.
WOOD USES
The most common uses for each timber in the
countries of origin and in the importing countries
when applicable are included in the timber descriptions.
The recommended uses for each timber
are also discussed in the descriptions and summarized
in table 9. These recommendations are
made on the basis of the timber’s combined physical,
mechanical, and machining properties. Only
those timbers most suited for each use are cited.
although other Caribbean species could be utilized
for the same purposes with some success.
The use made of timbers in the countries of their
origin is generally a good indication of their usefulness
and qualities, but often includes uses for
which they are not suited and may omit others
for which they are most suited. Timbers are often
utilized for many purposes simply because they
are readily available in good quantity at moderate
prices. Despite the many species growing in most
areas of the Caribbean, relatively few are produced
in commercial quantities. As a result, some woods
are used for certain purposes only, because other
timbers better qualified for those uses are not
readily available. Nevertheless, the local acceptance
of a timber for any specific use over a long
period indicates reasonably good service given for
that purpose.
SUPPLY
The paragraph on supply in each timber description
is based largely on information furnished by
interested governments in the Caribbean area.
This in no way implies that the timbers are not
available from other Central and South American
countries. Countries or areas having exportable
quantities of the different timbers are listed in
this section. Moderate quantities of some timbers
many become available from certain other Caribbean
islands and countries as the export demand
develops, but these are not listed as exportable at
this time.