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Aspen Bibliography Aspen Research
5-1948
The Preservative Treatment of Aspen The Preservative Treatment of Aspen
Frank H. Kaufert
University of Minnesota
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Recommended Citation Recommended Citation
Kaufert, F.H. 1948. The preservative treatment of aspen. United States Department of Agriculture, Forest
Service, Lake States Forest Experiment Station, Minnesota Agricultural Experiment Station, University of
Minnesota. Report No. 19.
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LAKE STATES ASPEN REPORT
NO.
19
THE
PRESERVATIVE
TREATMENT
OF
ASPEN
BY
FRANK
H.
KAUFERT
MINNESOTA
AGRICULTURAL
EXPERIMENT STATION
UNIVERSITY OF
MINNESOTA
AUG
3
11348
MAY 1948
PROCESSED
BY
U. S.
DEPARTMENT OF AGRICULTURE
FOREST
SERVICE
LAKE
STATES
FOREST EXPERIMENT
STATION
FOREWORD
During and
since World War II,
there
has
be on
increasing interest
in
aspen
(
Populv.s
trenuloides
)
in
the Lake States,
its
availability and supply,
properties
and
uses, and management;
Aspen is
a
tree of primary
importance
in 20 million
acres or
40 percent of
the total forest
area of
the
three
Lake
States
-
Michigan,
Minnesota, and
Wisconsin.
At an informal
meeting
at
Madison,
Wisconsin; in
January,
1947,
forestry
representatives
of several
federal, state,
and industrial groups in
the
Lake
States
agreed
that
it would
be desirable
to bring up
to date what is known
on aspen
and make it
available to
anyone interested. The job of preparing
this information in
the form
of reports
was assigned
to each of
the groups
listed below.
The reports will be
duplicated as rapidly as completed,
and
the entire project
should
be
finished by
the
end
of 1947. Each report will
concern one
aspect of the subject.
Copies will
be
available from
the
Ls.ke
States Forest Experiment
Station or from each
contributor.
Report
llumber
Subject
1
Aspen Properties and Uses
2 Aspen
Availability and Supply
3
Logging
Methods and Peeling of Aspen
4 Milling
of Aspen into Lumber
5
Seasoning of Aspen
6
Aspen Lumber
Grades and Characteristics
7
Mechanical
Properties
of Aspen
8
Machining
and Related
Properties of
Aspen
9
Aspen
Lumber
for 3uilding Purposes
10 Aspen for
Containers
11
Aspen for
Core Stock
12
Small
Dimension
and
Other Industrial Uses of Aspen
IE
Aspen for Teneer
14
Aspen for
Pulp
and
Paper
15 Aspen for
Cabin Logs
16
Aspen for Excelsior
17
Aspen
Defiberization
and Refining of
Product
18
Chemical Utilization of Aspen
19 Preservative Treatment of
Aspen
20
Marketing
of Aspen
21 Possibilities of
Managing Aspen
Contributors
to
Lake States Aspen
Reports
Lake
States
Forest Experiment Station, St.
Paul
1,
Finn.
Forest
Products Laboratory, Madison
5,
Wis.
Uorth
Central Region,
U.
S.
Forest
Service, Milwaukee
3,
Wis.
Div. of Forestry,
Univ. of Minnesota,
University Farm,
St.
Paul
1,
Minn.
School of Forestry and Conservation,
University
of
Michigan, Ann Arbor, Mich.
Department of Forestry, Michigan State
College, East
Lansing, Mich.
Michigan College of Mining
and
Technology, Houghton, Mich.
Superior Wood
Products, Inc., Duluth
2,
Minn.
Forestry Agent,
Chicago
&
ITorth
We
stern Railway System, St. Paul
1,
Minn.
REPORT
NO.
19
THE PRESERVATIVE
TREATMENT
OF ASPEN±
By
Frank
H. Kaufert
Division of Forestry
Agricultural Experiment
Station
University
of
Minnesota
1/
Aspen
is
one of
our least
durable woods and is known to deteriorate or
rot
rapidly under conditions favoring decay.
Records on aspen used under
moist
and severe decay conditions have shown that serious
decay and
failure
of
the
product may
develop in three
to four
years.
Some
present and potential uses for aspen involving
conditions favorable to
decay
and in which
this
lack of natural durability is a factor are:
(l) fence posts,
(2)
railroad cross ties,
(3)
mine timbers,
(h)
plank- .
ing for secondary
bridges,
(5)
sills
and other construction members in
buildings,
(6)
the lower logs of log cabins, and
(7)
small items as
pickets, stakes,
etc.
In all of these uses the wood in service
is either
in
contact
with the
soil
or is exposed to moisture for considerable periods, conditions that
result in rapid deterioration or development of decay in
woods lacking
natural durability
and
not protected by an effective preservative treat-
ment. Actually, aspen does not differ greatly from such hardwoods as
black ash, green
ash,
basswood,
hard maple, soft maple,
paper
birch,
yellow
birch,
and
Cottonwood in durability or behavior under conditions
favoring
decay.
None
of
these woods possess heartwood that
differs
appreciably from sapwood in decay resistance, and all of them
are
classed as species of low
durability. Although there
is
considerable
prejudice against aspen
for
uses
in
which decay
is not
a
factor
when
good
construction practices are followed,
for
such uses as siding,
roof
boards, sheathing, rafters, etc., experience has shown that aspen
is
as
durable as any wood, either hardwood or softwood,
under use
conditions
where it remains dry
or
is
exposed
to moisture for rela-
tively short periods.
The preservative
treatment
of aspen Is important only
for products
used
under conditions favoring decay, such as the products listed in
the
first paragraph,
which
are used in
contact
with
the
soil or which
may become moist
and
remain
moist for considerable periods. Unfortunately,
there is relatively little
published information on the treating char-
acteristics
of
aspen treated by different
processes and with different
preservatives.
Consequently,
most
of the information on
treating
char-
acteristics on which this report is based
was
obtained from discussions
with operators of wood preserving plants in Minnesota
and
Wisconsin, who
have
had
experience
with aspen, and from the unpublished results of
treating
l/
Published as University
of Minnesota Agricultural Experiment
Station
Misc. Journal Series
No.
623
tests made
at
the Forest Products
Laboratory and the
University
of
Minnesota. The service records
included in this
report
were
summarized
from
a
number of volumes
of the Proceedings
of the
American
Wood
Preservers' Association.
This report
includes
discussions
on the
wood
rotting fungi
responsible
for most
of
the
decay
of aspen
products,
decay
losses that occur during
seasoning, the
preparation
of
wood for
treatment
and
treating
characteristics,
experience
with
various treat-
ing processes,
the
available service
records on products
treated
with
different
preservatives
by several processes,
recommendations,
and
problems in need
of added research.
THE FUNGI RESPONSIBLE
FOR THE
DECAY OF ASPEN
As
Is true
for
practically all tree
species, rather distinct
groups
of
wood-rotting
fungi
are responsible
for
the
heartrot found in
living
aspen
trees
and
the decay
that develops
in aspen
pulpwood in storage,
in ties during seasoning, and in
all aspen products
used
in
contact
with the soil or under other moist
conditions.
Fomes
igniarius is responsible
for most
of
the heartrot
found
in
living
aspen. Aspen is relatively short-lived,
and trees on poor sites
may have
considerable heartrot caused
by this fungus
by
the time they
are h-0
to
50
years
of age
(2).
The same workers (Schmitz and Jackson)
also showed
that on
better sites
decay by Fomes igniarius may not become
a serious
limiting factor
until
stands reached
60
to
70
years in
age.
In contrast
to the heartrot of living
aspen
which is
caused mainly by
Fomes
igniarius
,
a
large number
of
wood-rotting fungi are capable
cf
attacking
and
causing decay
of
aspen products.
Some of
the most common
and important wood-rotting fungi found on decaying aspen products are
several species of Polyporus
(
hirsutus
,
pargamenus
,
versicolor
,
adustus
)
,
several species of
Por
ia
,
Femes applanatus
,
Pleurotus ostreatus
,
and
Armillaria mellea
.
Many other fungi may be found fruiting on
decaying
aspen products and may
cause
as
rapid decay as the more common wood rots
listed
above.
LOSSES DUE TO
DECAY
Because of
the susceptibility of
the wood to decay
and the high moisture
content of
both
sapwood
and heartwood, aspen
products may be
severely
attacked and
heavy losses due to decay may occur
during seasoning
or
storage unless
special precautions are taken.
Unpeeled aspen pulpwood
stored in the woods or
in wood
yards at mills
may
have numerous fruiting bodies or
sporophores of
wood-rotting
fungi
on
it after storage for one summer.
During particularly
wet
summers
or
under
very adverse
seasoning conditions,
as when pulpwood
is
stored in
brushy
areas in the woods, decay may
progress sufficiently
in one
season
to
cause
considerable loss. Normally, however,
unpeeled
aspen pulpwood
can be stored
through one summer season without
danger of
serious
loss,
even
though
there may be considerable
fruiting
of fungi.
During
the
second
season, decay
in unpeeled aspen pulpwood
progresses
very rapidly
-2-
and
decay losses are
usually high, particularly
when the
wood is
stacked
so
that there is
no space between stacks
for
air
circulation
or
where the
wood
yard
is
located in
a place with
poor
air
drainage.
Peeled aspen
pulpwood
usually decays
more slowly unless
the wood is allowed to remain
on
the ground too long after
peeling and becomes heavily infected
before
stacking. Normally,
peeled aspen pulpwood that
has been correctly
handled and is stacked under favorable conditions
can be held through
two
summer
seasons with
no
greater
loss than
occurs
in
unpeeled aspen during
one
season
of storage.
The problem of reducing
decay
losses
in aspen pulpwood during
storage has
ben
given relatively little
study.
It
is recognized that the
best prac-
tice
is
to limit
storage
to no more than
one season, and this procedure
normally is followed. Getting the wood off the ground as
soon as possi-
ble after cutting is important because it reduces the
chances of infec-
tion
by decay fungi before the
wood
reaches the
wood
yard
at pulp and
paper
mills. Stacking
so
that there is
good
air circulation between
piles and
placing
not
more than
two
8-
foot
stacks
together without
an
air
space between them
in yards where there is good air drainage are
also
generally
recognized
as being beneficial. The effect of spraying
fungicies or
preservatives
on
the
exposed ends of pulpwood sticks
in
storage
stacks was studied
by
the Division
^of
Forestry
of
the
University
of
Minnesota
in 19^0-^1.
Two fungicides £:/
extensively used
in the dipping
of
lumber
to
prevent blue stain and decay during seasoning were
used and
were
applied
to
the exposed ends
of pulpwood
sticks in storage
piles by
means
of
knap-sack sprayers.
The
fungicies were applied in May
19^0
on
unpeeled
pulpwood
cut and stacked in the yard during
the
previous winter.
Adjacent sections
of
the same stack were
left
untreated and acted as
controls.
Examinations in August
19^1?
after two summers
of
storage,
showed
a
marked difference in the number of
fruiting
bodies of
wood-
rotting fungi on the ends of treated sticks as compared to untreated
sticks.
Also,
there was much less decay near the ends of treated
sticks
than in untreated material. However, within
the stack, from
6
inches
to
1
foot
from
the ends, there was no
discernible difference between treated
and untreated material.
No pulping
studies were made on
this
material,
so it was not possible to say
whether
such
treatment would be economical
or
worthwhile in case
of wood for
which storage through two summers is
anticipated. End
treatment
of
pulpwood stacks has been
found
beneficial
by
some southern paper mills, and it deserves
further investigation
for
aspen pulpwood.
Serious decay losses may occur in aspen
ties
during
seasoning. Much of
the
prejudice
against
aspen
ties stems
from
the difficulty that treating
plant operators have experienced during seasoning. The high
moisture
content of
aspen
combined with its susceptibility to decay by a
large
number
of wood-rotting fungi makes it difficult to handle in
the same
manner as
ties
from
other
tree
species without danger
of
serious decay
losses. When regular stacking practices
(one-by-nine)
are
followed,
2/
Lignasan
(containing ethyl mercury phosphate as the active
ingredient)
and Powicide
G
or
sodium pentachlorophenate
„
drying
is
slow, and
during
poor- seasoning weather
decay
develops
rapidly
and
abundant fruiting
of fungi occurs at the
points
of contact
between
ties.
Although
decay may not develop sufficiently
during
one
summer to
affect
strength or the later serviceability
of well-
treated ties,
the
material
presents
a
bad
appearance,
and
the
contrast
between
aspen ties
and
ties of
other
species may be so great
under
poor seasoning
conditions
that
the prejudice that
has developed
against aspen
is quite
understand-
able
.
One
treating plant operator
reported that
decay during
seasoning
can be
greatly reduced by more
open piling
of
ties,
by stacking
one-by-seven
rather
than
the
standard
one-by-nine.
This practice
of providing
about
2- inches of
space
between ties permits
more rapid
drying.
Since
aspen
ties
are
not subject to
serious checking during
seasoning,
such
open
stacking can be followed
for
this
species, whereas it
would result
in
serious checking
of
red
oak, hard maple,
and
birch.
It is difficult
to
introduce
variations
in stacking practices,
and the cost
of such open
stacking
is
greater than the standard
one-by-nine practice,
but
it
offers
a possible solution
to the problem
of
reducing
decay losses
during
seasoning of aspen ties. Eeplacing the
cross
tie
used in self-
sticking with
a dry
2-by-4
has been suggested
as another means of
reducing
decay losses during seasoning. Whether this practice
is prac-
tical
is
not known.
Decay and
stain damage
to aspen lumber seasoning can be eliminated
or
held
to a minimum by
following the practices recommended in
Lake States
Aspen Eeport
No.
5
(Seasoning of Aspen).
Decay
damage
to aspen cabin
logs
can be reduced by
following
the handling practices
recommended in
Lake
States
Aspen
Eeport
No.
15
(Aspen for Cabin Logs). Decay damage to
aspen fence posts
and
other aspen products during seasoning
can
be
eliminated or reduced by peeling and open stacking to promote more rapid
drying. The
resistance
of
aspen
to checking
makes it
possible
to stack
posts
and other aspen products to promote rapid drying without danger of
serious checking.
TREATING PROCESSES AND PEESEEVAT
EVES
Whereas it is possible
to minimize or eliminate decay losses in
aspen
products during seasoning by modifications in
handling practices, the
only method of
insuring
a
reasonable
service life
or of
preventing rapid
deterioration of aspen products
used under conditions favoring
decay is
through
preservative treatment. As
previously mentioned, there has been
less experience with the
treatment of
aspen
than with the
treatment of
most of
the Lake States
wood
species used
for fence posts, ties,
mine
timbers,
and other
products commonly given
preservative
treatment. Also,
very
little has been
published on the treating of
aspen and most of
the
information
given here was obtained through discussion
with operators
of
treating plants.
Pressure
Treatment
At
least five pressure- treating
plants
in
Minnesota
and
Wisconsin have
had
experience with the
pressure treatment
of aspen ties,
aspen
bridge plank-
ing, mine
timbers,
and
fence posts. Most
of the experience
has been with
the
Lowry
and Eueping Empty-Cell
Processes and with
coal tar creosote,
and
zinc
chloride
has been used
to a limited extent.
Sawn
ties
incised
on all
four sides and hewn ties
incised on the
hewn surfaces and adzed
and bored
prior to
treatment
are
reported to treat rather
uniformly by the
Lowry
and
Eueping
Empty-Cell Processes,
and no special difficulties
have been
reported. In general,
the same is
true
for bridge
planking and sawn mine
timbers. In case
of unincised sawn or hewn aspen ties, large
fence
posts,
arid round
mine timbers,
rather erratic penetration
was reported.
End
penetration
of
preservatives
was excellent, but radial penetration
varied from
l/l6
inch to
1
Inch in the
same piece. This variation in
penetration
of
preservatives in different parts
of
the
same
piece
con-
stitutes one
of
the reasons
why
the preservative
treatment of round
aspen products
is
considered difficult. The presence
of tyloses in both
the
sapwood and heartwood of large- tooth aspen has been suggested as
a
possible
explanation
for
the irregular penetration
of preservatives in
wood
of
this
species (C.
H.
Teesdale and J.
D.
Mac Lean,
U. S.
Dept.
of
Agr., Bulletin
606,
1918).
The more uniform
treatment
of sawn aspen
products
can probably be traced
to
penetration through
exposed end-
grain
on
the sawn surfaces. This appears
a logical explanation because most
aspen lumber is cut from small logs, and there is abundant
end-
grain
on
the sawn surfaces associated with small knots and other
defects.
In
case of
incised
material,
penetration is
uniform because incising makes
tangential
and
longitudial penetration
possible in addition to radial
penetration.
Excellent penetration of coal
tar creosote in small aspen
posts (3-^-
inches top
diameter) was reported by one treating plant
experimenting
with
this material.
With larger posts, however, some difficulty
was
experienced in obtaining
uniform penetration of the
preservative.
Material
to
be given pressure
treatment with creosote
or
other oil pre-
servatives
should
be
free from bark
and
at
a
moisture
content below fiber
saturation,
30
per
cent. Better
results
are claimed In
treating material
at
moisture contents of
15
to
25
per
cent than drier
material.
Hot- cold
Bath Process
The
hot- cold bath process
(8)
has
been
used
experimentally
and by a number
of
small commercial treating
plants in
the
treatment of aspen fence
posts
and
mine timbers. Coal tar creosote,
water
gas
tar,
oil
solutions of
pentachlorophenol,
and
zinc chloride have been used in
this
process. Both
butt-
treatment
and
full-length treatment by
this process
have been tried.
In fence posts
in particular, spotty or erratic
penetration
at the ground
line,
the
critical
area,
has been
common
for
large posts.
Penetrations
varying from
l/l6
inch to
1
inch are not uncommon
in the ground-
line zone
of individual posts. This
is greater variation than
is commonly encountered
with
other
hardwoods and
far
greater than for
jack or
red pine,
for which
penetration
is usually very uniform and deep penetration
is
far more
easily
obtained. Excessive end penetration
of preservative
in aspen
posts
also
results
in waste of preservative
"because
such
end penetration
rarely
extends to the ground line,
where it
is
most
needed.
A
combin-
ation
of hand
incising
of
the
ground-
line area and
treatment
by the
hot-cold
bath process result in
deep and uniform
penetration
at the
ground
line without excessive
absorption
of
preservative
in the
butts.
However, such
incising is
slow and expensive
and has been
used
only
experimentally.
For small
aspen
posts,
3-^-
inches
top diameter, a
butt treatment
by the
hot-cold
bath
process
may
be all that is
needed for posts
used in
the
Lake
States, but
a
light
top
treatment
is
good
insurance
against
top rot
and should be applied wherever possible.
For larger posts,
some
top
treatment is essential because
of the danger
of top rot.
Top rot is
common
in larger posts
of all non-durable species,
whereas
it
is
rather
infrequent
in
smaller posts. This difference
is probably
due to the
tendency
of
the
tops
of larger
posts to retain
moisture for
long periods
following
heavy rains, thus favoring
top rot. Smaller
posts,
on the
other
hand,
appear to
dry
out so rapidly that there
is less opportunity
for top rot
to
develop.
Clean
peeling and careful air seasoning
appear to be as important in
treating by
the
hot-
cold
bath
process as for pressure treatment.
Non-
pressure Processes
Cold-soaking in oil solutions of pentachlorophenol
:
Considerable
experimental work has been done at the Forest Products Laboratory
and
at
the
University
of
Minnesota
on
the treatment of seasoned aspen posts by
soaking
in
cold-oil solutions of pentachlorophenol (l). Treatment has
been by
soaking
either full length or
by
butt treatment after air
seasoning
of
clean-peeled
posts.
The results
with
this process on aspen
have
been
very disappointing and
unsatisfactory
when
compared
to
results obtained
on jack
pine, red pine,
and
black
ash.
Penetration
of
preservative
at
the
ground
line
has been
found
extremely variable,
and
rarely
does it exceed l/k inch. In some
posts the penetration,
even
after long periods
of
soaking, has been no
more than l/l6 inch. Absorption of preservative
solutions by
posts may
be entirely satisfactory,
but most of the preservative is in the butts
in butt- treated posts and in
the
butts
and tops of
full-length treated
posts, with very shallow
and unsatisfactory penetration at
the critical
ground line zone.
The
process is simple,
and pentachlorophenol is an excellent wood
pre-
servative, but
the results
obtained have been disappointing
because of
the poor and
irregular penetration
of
preservative
'at the ground
line,
where treatment should be
deepest. The service data
available on aspen
posts
treated by this
process with pentachlorophenol (Table
3)
indicate
that
some
posts
may fail in
k
to
6 years, and
that
such
failure is due
to
spotty
or
shallow penetration and not
to
any fault of the
preservative.
-6-
Tire tube
treatment
with
zinc chloride
or chromated zinc
chloride;
A
con-
siderable number of
aspen posts have
been treated by
this process,
which
is
described in
a
statement
prepared by the Forest
Products Laboratory
(k
)
.
The published information
available indicates that
zinc
chloride, chromated
zinc chloride,
and other water-borne
preservatives move rather
rapidly
through
freshly
cut green aspen
posts when solutions of preservatives
are
applied to the butt
ends
by
this
process. Little is
known regarding
the
quantitative
distribution
of preservatives
in
posts but
the occurence
of
decay
in
the tops
of some treated
posts
after
5
to 8 years in service
indicates that in some
posts,
at
least, distribution is
not uniform.
The
results
of
service
tests indicate that
posts
treated
by this process
should last at least
10
years
(Table
3).
Although considerable decay has
developed in
many
of the posts treated by this process in the
7
to
8
years
that
have elapsed since they were set, their condition
indicates
that most of them will have at
least several
added years
of
life.
The process
is time-consuming
and
not well adapted to the treatment
of
large
numbers
of posts. Also,
there is some
question as
to
whether the
results
that
can be obtained are any better than those obtained by
treat-
ing with the
same chemicals
by a
simpler
and
cheaper process, designated
as the "butt-soaking process."
Butt- soaking
treatment
with zinc chloride or chromated
zinc
chloride:
This process was
first extensively tried at Cleitison College,
South
Carolina
on southern pine posts
(6).
The process
consists
of
immers-
ing the
butt
ends
of
freshly- cut unpeeled
posts in concentrated
solutions of
zinc chloride or chromated zinc chloride placed in shallow
vats, tanks, or drums. The concentrated solutions
move into the posts
by diffusion and
possibly by capillarity, The quantity absorbed can
be
controlled
to some extent by adjusting
the concentration of the treating
solution
and period of
immersion.
In rather extensive tests with this process
at the University of Minnesota,
it has been found
that
27
per cent or
33
per cent solutions
(3
or
k
pounds
per
gallon
of water) of chromated
zinc
chloride
are
preferable to
weaker
solutions.
By
immersing the
butts
of
freshly cut
aspen
posts in these
solutions
for two
days
and then
reversing the posts and immersing
the
tops for one-half
day,
absorptions
of
^
to
1-gr
pounds
of
the
preservative
per cubic foot of
wood
have been obtained (Table
1).
The
preservative
is concentrated in the butts
and tops
Immediately after
treatment, but
further distribution, sometimes rather uniformly throughout
the posts,
is obtained
by
setting the posts
on
their tops for two
weeks to
a
month,
Table 1
Variation
in absorption
of chromated zinc
chloride
solutions "by green
aspen
posts of
the same lot
when
treated by the butt-
soaking
process
Treating Period
Post
Top
Absorption
of
CZC
Wo.
Diameter
Butt
Top
in Ibs/cu
Treatment with a
27
per cent solution
1
3.6
2
days day
1.139
p
2 days
i
2
day
X..1T)[
3
4.3
2 days
1
2
day
1.416
4
3-9
2
days
1
2
day
1.270
5
3.3
2 days
1
2
day
1.256
6
3-7
2
days
i
2
day 1.800
7
3.1
2 days
1
2
day
1.975
8
4.3
2 days
2~
day
1.015
Treatment
wit!t a
20 per cent solution
1
4.6
2 days
i
day
.605
2 4.2
2 days
l
2
day
.630
3
4.6
2 days
1
2
day
.540
k
4.3
2
days
1
2
day
.544
5
3-9
2
days
1
2
day
•
5^9
6
3-3
2
days
i
2
day
.851
Service records
on aspen
posts treated by
this process
are not
available,
but
results
should be similar
to those
obtained
on
aspen
posts
treated
by the
tire-
tube method. Many
problems connected with this
treating
procedure
require
additional
work. Preliminary tests
indicate that
high
concentrations
of chromated
zinc
chloride
do
not
injure the
wood, but
this point needs further
study.
Also,
there
appears
to
be
considerable
difference in the
absorption
of preservative
by posts cut
on different
sites
or
at
different times
of
the year
(Table
2).
The
very
low absorp-
tions obtained
for
posts
cut
on
a
poor site near
New Brighton,
Minnesota
are particularly
disturbing.
The necessity
of using freshly
cut posts
or of removing
discs from the
ends
of posts
that
have
been
cut
for
several
days
is
a distinct
disadvantage
of the
process.
The
low
cost
of
the treating
chemicals
and
simplicity of the treating
process
are
advantages that give
the
process
some promise for
use by farmers
in
the
Lake
States.
Table
2
Variation
in Absorption
of a
27
per cent Chromated
Zinc Chloride
Solution
by Green
Aspen Posts
of Different
Lots When Treated by the
Butt-Soaking
Process
Lor,
No.
Date
Cut Source
Average
Top
No.
of
Days
Treating
Period
Ave. Absorption
of
preservative
(CZC)
Diameter
Posts
Butt
Top
lbs/cu. ft.
1 June
19^7
Cloquet, Minn.
3-7
8
2
1
2
1.39
2 April
1947
New
Brighton,
Minn.
3-7
12 2
1
2
.15
3
Feb.
1947
Cloquet, Minn.
h.2
8
2
1
2
77
k Feb.
1947
Cloquet,
Minn.
3*9
10 2
1
2
-99
Treatment
by Steeping:
Peeled aspen fence
posts and mine timbers
have
been
treated
by steeping
in
zinc chloride
and
chromated
zinc
chloride.
The process
consists
of soaking
green
peeled material
in
tanks
of
the
preservatives,
concentrations
of
5
per cent being
most commonly
used
(5).
The
preservatives
penetrate
by diffusion,
and the soaking
period is
normally
a week
or longer.
No
published service
records are
available
on
mine
timbers
treated
by this
process, but
one user
of
aspen
mine ties
steeped for
6 days
in
a
5
per cent
solution
of zinc
chloride reported a
life in excess
of 10 years.
The process is slow and
large tanks
are required, but
it
has some
application for mine timbers for which untreated
aspen is
not
satisfactory
and for
which
a
service life
of 10 to 12 years is
all that
is
desired.
Treatment by the Osmose Process:
A number of aspen
fence posts
have
been
treated
by the Forest Products
Laboratory with
Osmotite
and Osmosar
(Table
3).
These chemicals
were applied in paste form
to the
surface
of freshly
peeled green
posts
and the posts
bulk-piled and
covered with
a moisture-
resistant paper for a
period recommended by the
manufacture
of
these
preservatives. The preservatives
penetrate the green
posts
by diffusion
during
the bulk-piling
period and the posts can
be set when
removed from
the pile or after seasoning.
As indicated
by
the results of service tests given
in Table
3;
aspen
posts
treated
with
these chemicals develop early
decay, and the results
are far
inferior to
those
obtained with
the
same
chemicals on
pine posts.
This
difference
in results
on aspen
and pine
again
points to lack
of pene-
tration in aspen as the probable
cause of the rather
inferior results
obtained.
Treatment by Dry Salting: During
the
past
two years more than
four
hundred peeled green aspen posts have
been treated by the University
of
Minnesota by
a
process similar
to the Osmose Process.
This consists
of
applying a mixture of dry
powdered copper sulphate
and sodium dichromate
to green, freshly peeled aspen
posts as they are bulk-piled.
The posts
are given
a
half turn after
the upper surface has been covered with the
mixture of
these
chemicals,
and the application is repeated to cover the
remaining surface. This process permits concentration of the
preservative
at the ground line and top, where
treatment
is
most important.
Only
enough
preservative is
applied to the remainder
of
the
post to
give it
a
uniform color
.
This mixture of chemicals absorbs moisture from the
wood
very rapidly,
and
it
is usually
advisable
to allow the peeled posts to surface-dry
for
a day or so
to prevent excessive
loss
of
chemicals by drainage.
Although the chemicals react on the surface
of
the posts to form copper
chromate,
this
.iaterial appears to
be
sufficiently soluble to penetrate
the
wood
by diffusion.
Leaching
tests on treated wood indicate that
the
preservative is extremely resistant
to
removal
once
it has penetrated the
wood.
Penetrations
of
1/V
to
3
A-
inch
are
normally
obtained, and
distribution
is surprisingly uniform, considering the
method of
application. In
posts
treated to obtain
an over-all retention of
1
pound of the
preservative per
cubic foot but with treatment concentrated at the ground
line and top,
analyses have shown that
^
to
6
pounds of
preservative per cubic foot of
treated
wood may be present at
the ground
line.
In
tests
made to
date,
several mixtures of these
chemicals have beer-
tried:
(a)
Copper
sulphate
90
P
er cent and sodium dichromate 10
per cent
(b)
"
"
75
"
"
"
"
"
25
"
"
11 11
c/
-> 11 11
11 11 11
it 11
50
50
About 100 of
the
posts treated with these chemicals
by
this process are
now in
service tests,
but it is
too early to predict whether or not the
results will be better than
those obtained with other chemicals applied
by diffusion processes.
The
extreme resistance
to leaching shown by the
chenicals once they have
penetrated the
wood
suggests greater permance
than
has
been
obtained with
other water-borne
preservatives,
but
the
effectiveness of these
chemicals when applied
by
dry-salting
needs
to be
established through service tests.
Advantages of
the
method are its
low
cost
and
simplicity, no treating
equipment being required.
In
a trial
of
the process during
the summer
of
19^7
>
two men cut, peeled, arid treated
200
small
(3
_J
+
inch top diameter)
aspen
posts in one
day. With copper sulphate
at
$.07
and sodium
dichromate
at
$.12
per pound, the cost
of
chemicals per post averaged
$.08
when
a
50-50
mixture was used,
and
the posts were treated to obtain a
retention
of
approximately
1 pound per cubic foot, In
addition to labor
and
chemicals there was a small added cost
for
moisture-resistant crepe
paper, used in covering the
bulk-piled posts.
Disadvantages of the process are its
dirtiness and the difficulty of
obtaining sodium dichromate. Powdered copper sulphate
is
available in
most localities,
but
sodium dichromate^ must be obtained
through large
chemical
companies.
The
treated posts have a blue-green
or brown
color. Preliminary
corrosion tests on
wire staples
and
nails have
shown
that there is little
danger of corrosion to wire or fastenings
with
this
combination of
chem-
icals. However, additional tests
on.
this
point
are
needed.
The process
cannot
be recommended for the
treatment
of aspen
until
service
records are available, but it appears to have sufficient promise
to merit additional investigation.
Treatment with "Treater Dust": About
20
years
ago
a number of aspen
posts
were
treated
by the
University
of
Minnesota
by
applying "Treater
Dust," or
powdered white arsenic
(3);
to
the fence post holes and
around
the posts as
they
were set. This treatment resulted in some increase in
life of the posts but not
enough
to justify the cost. The average life
of small untreated aspen posts in these
tests
was
3-5
years and
for
posts
treated
with
"Treater
Dust"
it
was
5-2
years.
Miscellaneous non- pressure treatments: Dry aspen, posts
have
been
treated
by
applying several brush coats of creosote to the butts. There are no
service records
on
aspen posts treated in this manner, but experience
with other species
indicates that such
treatment with
a good
grade
of
coal
tar
creosote should at least double
the
life of small aspen
posts,
or increase it from about
3
years
to
5-6
years.
-11-
Brush and
spray
applications
of clear
oil solutions
of
pentachlorophenol
have been applied to aspen
cabin
logs after
the cabins
have
been
erected.
Except
for
the lower logs,
which may become
wet
from
rain
dripping
or
splashing, decay is not
a serious
factor
in cabin
logs.
Consequently,
as far
as prevention
of decay
is
concerned,
such
applications
have
little
value. However, such treatment
seems
to prevent
darkening
or
discolora-
tion of the logs.
Untreated aspen
logs,
like the
tops
of
aspen
fence
posts, soon take on
a
grey
or grey-
brown
color,
but
logs and
fence
posts
treated with light
oil solutions
of pentachlorophenol
retain
a much
lighter and cleaner
appearance.
Whether
this is
due
to the
prevention
by the
preservative
of growth
of staining
fungi
and molds
on
the
surface
or to other factors is
not
known,
SERVICE
RECORDS ON
TREATED ASPEN
Practically all of
the
published service
records available
on
aspen
treated
with different preservatives
and
by different
processes are
on fence
posts
.
These records are
summarized in
Table
3-
Although most
of these tests have
not
been established
long enough
to
obtain average service
lives,
the condition
of
the
posts
when last
examined
is
indicative
of the effectiveness
of the preservatives
and
treating methods.
Relatively few service records
on
aspen
posts
pressure-treated with coal
tar
creosote are available. The
results on posts
treated with this
preservative in
mixture with gas
oil
(25
per cent coal
tar creosote and
75
per
cent
gas oil) indicate that
aspen posts pressure-
treated with this
mixture
or with
other
creosote- oil
combinations should give
good
service
(Table
3)-
Although this particular
group of posts was
given
a rather
heavy treatment,
they
were
in excellent condition after 22 years
of
service. There are more service
records on pressure-treated Cottonwood
than on
pressure-treated aspen.
Cottonwood posts
given
a
good pressure
treatment
with coal tar creosote are known
to
give
20 to
25
years
of
service. The similarity
in treating characteristics of
aspen
and
cottonwood
suggests that equally
good
results
should
be obtainable with
pressure-treated aspen posts. Because of the greater uniformity in
penetration obtainable with small aspen posts, more uniform results
should
be
possible with smaller posts
than
with larger material. The
results on posts given a pressure treatment with a
2.
9.
per cent solution
of
tetrachlorophenol in crank case
oil (Table
3)
indicate that aspen
posts
pressure-treated with
oil
solutions
of the
chlorophenols, partic-
ularly
with
pentachlorophenol, should given
service similar to
material
treated with
coal
tar creosote.
All of the available service records on
aspen posts
treated by the hot-
cold
bath process
are
on full length treated material.
After 10
years
of
service
those posts treated with coal
tar creosote by
this
process
are
still in excellent condition (Table
3).
Because of.
the
full-length
treatment
no
top rot has developed. However,
there is
real danger of
failure
due
to top
rot in large aspen posts given
only a butt
treatment
by
the hot-cold process. As indicated previously,
thorough butt
treatment
-12-
of 3"^
inch aspen posts
and
a
very
light
top
treatment
appear
to be all
that
is needed because
top rot does
not develop
to an important
extent
in
small posts of nondurable
species
used in the Lake
States,.
For larger
posts,
however, a
good
top
treatment
should be given
in
addition to butt
treatment. This top
treatment might
consist
of
a
few hours soaking
in
hot
oil
with
the tops immersed
to
a
depth
of
6-12
inches.
The
service tests
on aspen posts
treated
by
cold
soaking in oil solution
of
pentachlorophenol
(Table
3)
have
not run
long enough to permit final
conclusions, but the erratic
and
shallow penetration at the
ground line
zone, coupled with early
failure
of
a number
of posts, suggests that
this
treatment will not prove
as satisfactory for aspen
posts as for
jack
pine,
red pine, and southern pine posts.
More aspen posts
have
been
treated
by
this
process and are in service tests
than for any other preservative or
treating procedure. Consequently, we
should
have
a
good
evaluation of the
process in a
few
more years.
The
results given
in Table
3
on water-borne preservatives applied
by
various processes reflect not
only the variability in absorption
of
preservative
that appears
to be
characteristic for aspen but the lack
of
resistance to leaching
inherent in most of these
preservatives.
It
is questionable whether a service
life of more than
10-12
years
can be
obtained for aspen products treated with these water-borne preservatives
even though good
absorption
and
distribution are obtained. Treatment
of
aspen with these water-borne preservatives appears to be advisable only
for
farm use
and
possibly for some types
of
mine timbers. Since treatment
with these
preservatives
may increase the service life of
aspen
fence
posts
to
10
years or somewhat longer, as compared to
3
_j
+
years for untreated
posts, the
use
of
these water-borne chemicals and various
non-pressure
treating processes
can
be
very
economical and advantageous
to
the
farmer
owning aspen timber of post size,
Service records on
aspen ties
No
published
service records are available on treated
aspen ties. One
Lake
States railroad installed a large
number
of
pressure- creosoted aspen
ties in one of
their tracks
15
years
ago
and has observed these
ties
since
that
date.
The ties were hewn on two faces and
most
of
them were
very large. The ties were
not
adzed or bored prior to
treatment, and
this fact many account for much
of
the difficulty that
has been experi-
enced
with them. Absorption of about 8 pounds of a good grade
of coal
tar creosote per
cubic foot
was obtained, and increment-borer
measure-
ments indicated that penetration was excellent on the
unslabbed surfaces
but
was
more
spotty and
not
as deep
on the
slabbed surfaces. After
15
years of
service these
ties have
an excellent
surface appearance.
They
are very free
from checks and there is
no
outward
evidence
of
deterior-
ation. However, at the time
of examination
(19^?),
many of
the spikes
were
loose.
This loosening
of spikes has been
prevalent
for
these ties
for
a number
of
years and is
attributed
partly
to
the poor spike- holding
quality
of aspen and partly to the development
of
decay in the
interior
of
the ties
around the spike holes.
The wood
around the loose
spikes
-13-
below
the
treated zone was soft and
appeared to be
decayed in a number
of
ties. Had
these ties been
bored
and adzed
prior
to treatment
there
would
have been
little
chance
of decay developing
around the spikes,
and
the
difficulty
with spike-
loosening
undoubtedly would have
been less
serious
.
Several other
railroads have
used treated aspen ties
in the past.
Their
greatest objection to these ties was not
their durability
or service
lives, but the
difficulty
experienced in
seasoning and with
spike
loosening. In
the
opinion of these
users, aspen ties
that
are
adzed
and
bored
prior to treatment
and are given
pressure treatment with
a good
grade of
coal tar creosote
should have
as good
service
lives as similar
cottonwood ties, for which service lives
of 20
to
30
years
have been
obtained
(7).
The problem
of spike-loosening
is
less important
with
heavier
tie plates
and
the adoption
of
adzing and boring prior to treat-
ment as uniform
practice, but it is
still important on curves.
Aspen
is known to have lower nail-holding properties than
woods of similar
density,
but whether this difference
is sufficient to rule out
a greater
use
of
aspen for ties is not certain.
The. similarity of aspen and
cottonwood
in most properties,
including nail-holding, indicate that it
should
perform as well as the latter species when given the
same
treat-
ment
and
used under the same conditions.
Service records on
aspen
mine
timber
No
published
service records are available on treated aspen mine timbers,
but the experience of
several users indicates
that
when
properly
treated
this
wood
performs about as well as most
of the hardwoods
used. In
general, however,
results
appear
to
be
inferior to
those
obtained with
jack pine and other conifers, probably because of the
greater difficulty
of obtaining uniform
treatment
of
aspen.
Service records
on
treated aspen bridge planking
Pressure-creosoted
aspen bridge planking used
in secondary bridges has
given excellent results in Minnesota. Several reports
were obtained of
planking
that was
in
good
condition after
10
years
of service.
The
resistance
of
aspen to checking
and to
wear, under conditions where
only
light
traffic is involved, combined with the excellent
treatment
that
can be obtained with sawn aspen products, makes pressure creosoted
aspen
bridge planking
a
very satisfactory
material.
-Ik-
Table
3«
Service Teste
on Aspen Fence PostB Treated with Different Preservatives by Several Processes
Absorption
Top Date Average
Agency
Making Test
Posts
Set at Preservative
lbs. per
cu.
ft.
Number
Set
Diameter
( inches
)
Set
Last
Examined
Condition
Decaying Failed
Servicf
(years
Treated by the Tire Tube Method
Por
prod . Lab Madison,
Wla.
Zinc Chloride
.14 to 1.88
lt-8
1937
I9U5
42 2
For.
Prod. Lab.
Madison,
Wis.
Cnromated Zinc Chloride
.64 to
1.35
28
4-8
1937
19U5 28
For.
Prod. Lab. Madison, Wla.
Sodium
Chromate .22 to 1.20
3
4-8
1937
19"*5
1 2
For.
Prod. Lab. Madison, Wla. Copper
Sulfate
.12 to
.54
17
4-8
1937
191*5
13
1
Lake
States
For.
Exp. Sta.
La Crosse, Wis. Zinc Chloride
.5
to
.75
15i/
4-7
1938
191*5
l_,tLK
e
OlalDD r or . Exp. Sta. La
Crosse, Wis.
Zinc Chloride
.5
to
.75
152/
4-7
1938
191*5
Treated by
Diffusion Process
-
Chemical In
Paste Formed Applied to Peeled Green Posts as Recommended by Osmose Corporation
For. Prod.
Lab. Madison,
Wis. Osmosar
.29
16 5-7
1936
1946 16 14 6.4
For.
Prod. Lab. Madison, Wis. Osmotlte
.23
7
5-7
1936
191*6
7
6 6.6
For. Prod. Lab.
Drummond, Wis. Osmosar
.29
49
5-7
1936
191*6
45
18
For. Prod. Lab.
Drummond, Wis. Osmotlte
.23
55
5-7
1936
191*6
51
12
Treated With Oil
Solutions
of
Pentachlorophenol by Cold Soaking
•-
Treating Time
Given
In
Preservative Column
For. Prod.
Lab. Oregon, Wis. 8 hrs.
-
full length
a.83/
9
4
1943
191*6
8
3
For. Prod. Lab. Oregon,
Wis
.
24 hrs.
-
full length
9
3.7
19l»3
19U6
4
For, Prod. Lab. Oregon, Wis
.
48
hrs.
-
full length
k.^
9
3.7
1943
191*6
3
__
For. Prod.
Lab.
Oregon,
Wis.
96
hrs.
-
full
length
5.^
9
3.8
1943
1946
1
„
For. Prod. Lab. 168
hrs.
-
full length
5.5^ 8
3*5
I9U3 19U6
2
__
U. of
Minn.
Cloquet, Minn.
18 hrs.
-butt,
6
hrs. -top
4.6^
30
3-5
19lt2
19"*6
' -
U. of Minn.
Cloquet, Minn. 40 hrs. -butt, 8 hrs.
-top
3.5*'
30
3-5
19U2 1946
-
U. of Minn.
St. Paul, Minn. 18 hrs. -butt, 6 hrs. -top
20
3-5
19l*2
1946
-
4
U. of
Minn. St.
Paul,
Minn.
Ho hrs. -butt, 6 hrs. -top
2.8^
20
3-5 19U2 1946
-
2
—
U.
of Minn.
Waseca, Minn. 18 hrs. -butt, 6 hrs. -top
2.9*'
20 3-5 19U2
191*6 2
U.
of Minn.
Waseca, Minn. 40
hrs.
-butt, 6 hrs.
-top
20 3-5
19l*2
1946
--
D.
of
Minn.
Cloquet, Minn. Untreated None
30
3-5
19U2
191*6
30
2.8
U.
of Minn. St.
Paul, Minn. Untreated None 20
3-5
19l*2
1947
9
11
3-4
U. of
Minn. Waseca, Minn.
Untreated None 20
3-5
191*2
1946
3
17
3-1*
Lake
States
For.
Eip. Sta. La Crosse, Wis. Untreated
None
15
4-7
1938
1941
15 15
2-3
Hot-Cold Bath
For. Prod. Lab.
Madison,
Vis.
Coal Tar Creosote
(Full
length treatment)
9.U 10
1.-5
1936
1947
For.
Prod.
Lab. Drummond,
Wis.
Coal Tar
Creosote
(Full length
treatment)
ll.lt
25
3-5
1936
1946
--
For.
Prod. Lab. Madison, Wis.
Zinc
Chloride
(Full
length treatment)
1.32
6U
4-8
1937
191*5
63
Pressure Treatment
For. Prod. Lab. Madison,
Wis. Tetrachlorophenol
7.5*/ 10 5-7
1936
19"*7
6
For.
Prod. Lab. Drummond, Wis. Tetrachlorophenol
8.2V
22
3-6
1936
1946
3
For. Prod. Lab. Madison, Wis.
25%
coal
tar
creosote
and
75i
gas
oil
16.1 20
5-7 1916
1938
1/
Posts
set with bark
on.
2/
Posts peeled before setting.
3/
Absorption in
pounds of a
5-0
solution of pentachlorophenol
in
fuel
oil or
kerosene.
kf
2.9
percent solution
of
tetrachlorophenol in crank case oil.
Dashes
(
—
) indicate that records were not taken
or
are not available.
-15-
Summary and
Recommendations
on
The
Preservative Treatment
of Aspen
Because
aspen
possesses
no
natural
durability, all aspen
products
used m
contact
with
the soil decay rapidly, and such
products as
untreated aspen
fence
posts rarely last more than
3
to
k
years.
When aspen is
used
for
sills of
buildings, bridge planking,
and the
lower logs
of log cabins,
where the products
are not
in contact
with the soil
but may
become moist
and
remain moist
for considerable
periods,
deterioration
by decay
may
also develop rapidly.
Aspen
products to be given preservative
treatment
with coal tar
creosote
or with oil solutions of pentachlorophenol and copper
naphthenate
must
be
cleanly peeled and free from inner
bark. All aspen
products
to be
given
treatment
with
any
of
these
oil
solutions must be
well air-seasoned.
To
avoid
possible losses
from
decay
during seasoning, aspen
ties, fence
posts,
mine timbers, and planking
should be openly
piled to promote rapid
drying.
Aspen does not check
as badly as the heavier
hardwoods
and
can
be more openly
stacked without danger
of serious checking.
Aspen
planking, sawn ties, and sawn mine timbers
can be readily treated
with coal
tar creosote by the Rueping
and Lowry Empty-Cell pressure-
treating processes. The
same is
true
for
ties
that
are
incised, adzed
and bored
prior
to
treatment.
Although there has been less experience
with the
treatment
of
these aspen
products with other preservatives, it is
logical
to
assume that similar results
could be obtained
with
oil solutions
of
pentachlorophenol or
copper naphthenate
applied by the empty- cell pro-
cesses,
and with water-borne
preservatives,
such as zinc chloride,
chromated
zinc chloride, and various proprietary compounds, when applied
by the
full-cell
pressure- treating process.
In
case
of
large
round
aspen products, such
as fence posts and mine timbers, some difficulty
has been encountered in
obtaining uniform penetration by
the
pressure
treating processes.
The
limited experience reported on the treatment
of
aspen products by
the
hot-
cold bath process
indicates that fairly satisfactory treatment can be
obtained
in
case of
sawn products and small round fence posts, but that
penetration
may
be spotty
in critical areas
of
large round posts (over
5
inches
in top
diameter)
and
other large round aspen products.
The
published
information indicates that
only
coal tar creosote and
zinc
chloride
have
been
applied to aspen
by
this process, but it
is
logical
to assume
that suitable oil solutions
of
pentachlorophenol
and copper
naphthenate
could
be applied with similar results.
Small aspen posts
(3-^
inches in top diameter)
do
not benefit as much from top
treatment
as
large
posts
(5
inches and over in top diameter),
but some
treatment to
protect the tops from top rot is advisable. When
given thorough
treat-
ment
by
pressure
or the hot- cold
bath process, aspen posts
with
inch
top
diameters should be adequate for all fencing
uses except
corners,
and the
use
of
larger posts is
not
recommended.
-16-
A
considerable
number
of
seasoned aspen fence
posts have been
treated
with
oil
solutions of
pentachlorophenol by cold-
soaking. The erratic
and
shallow
penetration
obtained
with this process
to date indicates
that it
cannot
be satisfactorily
used with this
species unless some
cheap and
simple method of incising the
ground line area
can be
found.
Green
aspen
fence posts
and mine timbers have
been treated
with water-borne
preservatives, such
as zinc chloride,
chromated zinc chloride,
and several
proprietary
compounds,
by
the
steeping,
the tire-tube, the
butt-soaking,
and
several
diffusion processes.
Although
treatment
with water-borne
preservatives by all
of
these
processes is
not
always
uniform and the
results in many
cases
have been
disappointing, the average service
life
of
aspen products can
be increased sufficiently
through such treatments
to
warrant the
consideration
of
these processes
for
the treatment
of posts
by
farmers
and
for the treatment
of some types
of
mine timbers.
Increased
service
or
resistance
to
decay can
be
achieved
by brush- coat ing
dry aspen lumber, fence posts, or other aspen products
with several coats
of coal
tar creosote or with oil
solutions of pentachlorophenol and
copper naphthenate. Such treatment is suggested
when
aspen must
be used
for farm building
items subject
to decay and when no more thorough method
of
treatment can
be
employed,
The
treatment
of aspen
cabin
logs
with
several brush coats of
a
clear oil-solution
of
pentachlorophenol keeps
the logs
from darkening
to
the same extent as untreated
logs.
Most
of
the published
service
records on
pressure-
and hot=cold
bath-
treated aspen products are
on
fence posts treated
with
coal
tar creosote.
These records
indicate that service lives
of
over
20
years or service
similar
to those
obtained
with
other
woods
treated with
the
same
pre-
servative
can
be obtained for aspen
given thorough treatment by these
processes. On the
basis
of
the results obtained on
aspen posts
treated
with
a
crank-case oil solution of
tetrachlorophenol, and
the generally
recognized superiority of pentachlorophenol
over tetrachlorophenol,
results
similar
to
those obtained with coal
tar creosote should be
obtainable on aspen
products treated
with
suitable oil solutions of
pentachlorophenol by
pressure
or
hot-
cold
bath treating
processes.
The service records on
aspen
products
treated with
water-borne pre-
servatives indicate that
service lives
of
at least
10
years
should be
obtainable for well treated products. Although
some decay may develop
during
this
period
because
of
leaching
of
the preservatives,
the avail-
able service
records
indicate that service records
of 10
or
more years
usually can be
expected
of products well treated
with water-borne
pre-
servatives
,
-17-
Problems Associated With the Preservative
Treatment
of
Aspen that Need Study
Although
practically every
aspect
of
the preservative
treatment
of
aspen
needs
study, the following problems particularly
need attention:
1.
The air seasoning of aspen ties,
mine timbers,
fence
posts, and other
aspen products
.
Can the serious
losses from
decay now frequently
encountered when following stacking
practices
worked
out for
other species
be reduced by more open stacking
without incurring
serious
checking
losses?
2
.
Reduction
of
end absorption
in treatment
by the hot-
cold bath process.
Can
excessive
absorption
of
creosote
and other preservatives
in the butts
of aspen,
where
it does little
good, be reduced
by end
coatings
or other
methods
?
3.
Size
of
aspen fence posts.
What
size
aspen
post is needed
to provide
adequate strength and over-turning resistance,
provided the
post receives
an effective preservative treatment?
k.
Spike holding properties
of aspen ties. Is
this an important
factor
when
ties are incised, adzed,
and bored prior
to treatment and
when new
types and larger tie plates
are used?
5=
Cold-soaking
in
oil solutions of pentachlorophenol
.
Can anything
be done to
improve the
ground-line penetration in seasoned aspen
posts
treated
by
this
simple and
relatively
low
cost process.,
which is so
promising for many other species?
6.
Creosote-petroleum mixtures.
To
what extent
can coal tar creosote be
diluted with the cheaper petroleum
oils and still produce effective
treatment
by
the
pressure
and hot- cold bath treating processes?
7.
Service records
on
treated
aspen products. The service records
on
aspen treated with water-borne preservatives
are completely inadequate,
and much additional
material
should be installed in service tests.
The
same
is
true
for
aspen treated with
oil
preservatives
by the pressure
and hot-cold bath
treating
processes.
8.
Treatment
by
simple
diffusion
processes.
Much work
is needed
on
the simple diffusion- treat ing process described in this report. Other
chemicals and combinations
of
chemicals should be
"tested
in addition
to further tests on the chemicals
already
tried.
9.
Butt-
soaking
treatment.
Chemical analyses are needed on aspen
posts
treated by this process to determine
how
uniformly
preservatives are
distributed, Also, tests
should
be
made on
aspen posts cut from various
sites at different
times
of the year to establish the variability that
may
be
encountered.
-18-
10 .
The effect o:u
strength
of high
concentrations
of water-borne preser-
vatives
.
Added tests
are
needed to determine whether
the high concen-
trations of chromated
zinc
chloride in the
butt-soaking
process seriously
affect
strength.
References
1.
Blew,
J.
Treating
wood in
pentachlorophenol solutions
by
the
cold-
soaking
method.
Forest Products
Laboratory Mimeograph
MM5.
1948,
2.
S chm.it
z,
H„
and L. ¥.. R.
Jackson
.
Heartrot
of
aspen.
University
of
Minnesota Agricultural Experiment Station Technical
Bulletin
No.
50,
1927-
3„
Schmitz,
H.
Unpublished report in
files
of
Division
of
Forestry,
University
of
Minnesota.
1936.
k.
Wirka,
R s
M.
Tire-tube method
of
fence-post
treatment. Forest
Products
Laboratory
Mimeograph
RH58.
19^5
•
5«
Wirka, R,
M. Preservation of timber by the
steeping process,, Forest
Products Laboratory
Mimeograph
R621
,
19^-3
6..
Circular
262,
Clemson
Agricultural College, Clemson,
S,
C.
7.
Proceedings of the American
Wood
Preservers' Association, Tie
Service
Records,
1939,
1942,
and
19^3.
8.
Selecting
a
suitable
method
for
treating fence
posts. Forest Products
Laboratory
Mimeograph
No» R1468,
1946.
-19-
