2

Assessment of

the Treatability of 

Small-Diameter

Grand Fir Posts 

Stan Lebow 

Susan L. LeVan 

Jeffrey J. Morrell 

Nils D. Christoffersen 

United States

Department of 

Agriculture

Forest Service 

Forest

Products

Laboratory

Research

Note

FPL−RN−0285
Abstract 

The value of small-diameter grand fir round stock could be 

increased if this material could be successfully treated with 

preservatives and marketed as posts and poles. This paper 

reports the treatability of suppressed-growth grand fir posts 

with several common preservatives. Ammoniacal copper 

zinc arsenate (ACZA) and oilborne copper naphthenate were 

found to provide adequate treatment. Acceptable treatment 

was not achieved with chromated copper arsenate (CCA). 

The pattern of preservative penetration was erratic, especially with CCA. 

Keywords: grand fir, small diameter, treatability, 

preservative, chromated copper arsenate, copper 

naphthenate, ammoniacal copper zinc arsenate 

May 2002 

Lebow, Stan; LeVan, Susan L.; Morrell, Jeffrey J.; Christoffersen, Nils D. 

2002. Assessment of the treatability of small-diameter grand fir posts. 

Res. Note FPL-RN-0285. Madison, WI: U.S. Department of Agriculture, 

Forest Service, Forest Products Laboratory. 4 p. 

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an equal opportunity provider and employer. 
Assessment of the Treatability of 

Small-Diameter Grand Fir Posts

Stan Lebow, Research Forest Products Technologist

Susan L. LeVan, Program Manager

Forest Products Laboratory, Madison, Wisconsin 

Jeffrey J. Morrell, Professor

Department of Wood Science and Engineering, Oregon State University, Corvallis, Oregon 

Nils D. Christoffersen, Program Manager 

Wallowa Resources, Enterprise, Oregon 

Introduction 

In some areas of the western United States, National Forests 

contain dense stands of small-diameter grand fir (Abies 

grandis). Management objectives for these forests often call 

for removal of a portion of this material, but these trees 

currently have low commercial value. The value of smalldiameter grand fir round stock could be increased if this 

material could be successfully treated with preservatives and 

marketed as posts and poles. However, the treatability of this 

species is not well established. One study of western species 

reported that the treatability of grand fir lumber with chromated copper arsenate (CCA) was greater than that of western hemlock and the true firs (Lebow and others 1996), 

while earlier work suggested that grand fir was among the 

least treatable of the commercial Hem–Fir group (Kumar and 

Morrell 1989, 1990). In a more recent trial (Rhatigan and 

Morrell 2000), grand fir round stock was adequately treated 

with ammoniacal copper zinc arsenate (ACZA), but penetration was substandard with CCA (Table 1). Although greater 

penetration is typical with the ammoniacal preservatives, the 

extent of the disparity in penetration between ACZA and 

CCA was greater than expected. 

Copper naphthenate presents another possibility for treating 

grand fir. This preservative may offer marketing advantages 

over both CCA and ACZA because it does not contain 

arsenic and is not a restricted use pesticide.1

 Copper 

naphthenate is the reaction product of naphthenic acids and 

copper compounds dissolved in oil. Copper naphthenate is 

used for treating utility poles and in highway construction; it 

is not used as widely as creosote or pentachlorophenol. The 

properties of copper naphthenate, like those of pentachlorophenol, depend on the type of oil in which it is dissolved. 

Commonly used oils are fuel oil and mineral spirits. The 

color of the treated wood varies from light brown to dark 

green, depending on the type of oil and the treating process. 

The purpose of this study was to further investigate the 

treatability of grand fir round stock with CCA and develop 

data on the treatability of this species with copper 

naphthenate. 

Materials and Methods 

Sections of grand fir round stock were obtained from the 

Wallowa Mountains in Wallowa County, Oregon. Twenty 

0.9- to 1.2-m-long sections were cut, debarked, air dried to 

below 25% moisture content, and shipped to the Forest 

Products Laboratory in Madison, Wisconsin. Two posts 

were discarded because of heavy sapstain, which can sometimes increase permeability. The remaining 18 posts, which 

ranged in diameter from 69 to 112 mm, were further conditioned to between 10% and 15% moisture content. Approximately 76 mm was removed from the end of each post; 

the posts were then cut into three 254-mm-long specimens. 

 

1

The Environmental Protection Agency has determined that 

some pesticides, even with proper handling and application, 

might result in an adverse effect on human health and/or the 

environment. These pesticides are classified as restricted use 

pesticides, and can only be applied by persons who have 

been trained in their use. CCA, creosote, and pentachlorophenol are examples of wood preservatives that are restricted 

use pesticides. 

Table 1—Penetration of ACZA and CCA in grand fir posts 

at Oregon State University post farma

 

Preservative 

Average penetration 

(mm) 

Cores meeting 

penetration standardb

(%) 

ACZA 42 100 

CCA 15 56 

a

Rhatigan and Morrell 2000. 

b

AWPA Standard C5. 
2 

The specimens were end-coated with neoprene rubber 

sealant to limit end-grain penetration. One specimen from 

each post was randomly assigned to one of the following 

treatment groups: 

1. CCA–C treatment: 2% solution—Full cell, 30 min 

initial vacuum (–85 kPa) followed by 60 min pressure at 

1,035 kPa 

2. CCA–C treatment: 2% solution—Full cell 30 min initial 

vacuum (–85 kPa) followed by 300 min pressure at 

1,035 kPa 

3. Copper naphthenate treatment: 1% solution (as copper, 

in #2 fuel oil)—Full cell, 30 min initial vacuum 

(–85 kPa) followed by 300 min pressure at 1,035 kPa 

All treatments were performed at room temperature. Following treatment, the specimens were allowed to air dry, cut in 

half to expose the cross-sectional face, and sprayed with a 

Chrome Azurol-S copper indicator solution. The distance 

from the edge to the first void in preservative penetration 

was measured at four equally spaced points around the circumference of each post. The depth of penetration was 

compared to American Wood Preservers’ Association 

(AWPA) Standard C5 for fence posts (AWPA 2001). 

Results and Discussion 

Despite their small diameter, many grand fir trees evaluated 

in this study were more than 50 years old and had more than 

16 growth rings/cm in the outer 25 mm (Table 2). Most trees 

contained some readily visible areas of compression wood. 

These characteristics all reflect the adverse growing conditions endured by the trees. 

Penetration of CCA into the grand fir specimens was generally poor, in agreement with the findings of Rhatigan and 

Morrell (2000). Penetration was only slightly improved by 

increasing the pressure period from 1 to 5 h (Table 3). The 

greatest degree and uniformity of penetration was achieved 

with copper naphthenate. It appears that copper naphthenate 

will provide penetration sufficient to comply with AWPA 

Standard C5 (AWPA 2001) for difficult-to-treat western 

species used as round fence posts.2

 That standard calls for a 

minimum of 9 mm of preservative penetration in the outer 

portion of at least 80% of the posts sampled. For specimens 

treated with copper naphthenate, 67 of 72 measurements 

(93%) met or exceeded the 9-mm requirement (Table 3). 

Neither of the CCA charges would have met this penetration 

standard. These results illustrate that the type of solvent used 

can greatly influence the ability of a preservative to penetrate 

the wood. 

 

2

Grand fir is not currently listed in Standard C5. For the 

purposes of this report, preservative penetration for grand fir 

was compared to the criteria for the combined Douglas-fir, 

western hemlock, and western larch listing. 

The treatability of grand fir varied greatly between trees. 

There appeared to be a slight correlation between the rate 

of growth of the tree and the degree of copper naphthenate 

penetration. Younger, faster-growing trees tended to be more 

treatable with copper naphthenate (Fig. 1). This suggests that 

grand fir growing under conditions more favorable than 

those in this study might be more readily treated. Little 

correlation was apparent between treatability and either stem 

diameter or extent of compression wood. 

The pattern of preservative penetration was erratic and unusual, especially for the CCA treatments (Fig. 2). Unlike the 

“treated shell” appearance that usually results when only the 

sapwood portion of round stock is penetrated, many CCAtreated grand fir specimens had a thin layer of treatment on 

the outside, a broad band of untreated sapwood, and another 

band of treated wood near the center of the tree. CCA apparently penetrated the inner portion by flowing into drying 

checks until it reached more permeable wood. It then spread 

tangentially around the stem in those areas. Even with the 

copper naphthenate treatment, occasional skips or breaks in 

penetration occurred (Fig. 2). Incising would help to eliminate these irregularities in penetration, but the cost of acquiring equipment capable of incising small round-stock might 

be prohibitive. Further investigation may be warranted to 

determine the wood microstructure characteristics responsible for these unusual preservative penetration patterns. 

Table 2—Characteristics of grand fir posts treated with 

CCA or copper naphthenate 

Post 

number 

Age 

(years) 

Growth 

rings/cma 

Post 

diameter 

(mm) 

Degree of 

compression 

wood 

1 >50 11 103 Severe 

2 >50 >16 91 Moderate 

3 >50 >16 93 Mild 

4 >50 >16 80 Mild 

5 >50 >16 91 Moderate 

6 45 10 100 Severe 

7 >50 >16 74 Mild 

8 >50 >16 78 Mild 

9 >50 >16 76 Moderate 

10 20 6 79 None 

11 >50 >16 69 Mild 

12 >50 14 112 Moderate 

13 19 5 72 Moderate 

14 19 6 97 None 

15 20 4 96 Mild 

16 20 6 87 None 

17 31 8 100 Mild 

18 >50 >16 94 Mild 

a

As counted in outer 25 mm of post. 
3 

Table 3. Preservative penetration measured in 4 quadrants in grand-fir post sections 

pressure treated with CCA or copper naphthenate 

Penetration (mm) Treatment 

and post no. Quad. 1 Quad. 2 Quad. 3 Quad. 4 Post avg. 

Number 

failed posts 

Percentage 

passed postsa

CCA—1 h pressure 

1 30 1 35 10 19.0 1 

2 1 10 1 1 3.3 3 

3 1 28 1 1 7.8 3 

4 15 1 1 1 4.5 3 

5 1 1 14 1 4.3 3 

6 1 30 2 20 13.3 2 

7 2 15 1 1 4.8 3 

8 1 1 1 1 1.0 4 

9 20 1 15 2 9.5 2 

10 1 2 30 20 13.3 2 

11 20 2 2 2 6.5 3 

12 15 2 5 20 10.5 2 

13 1 1 6 1 2.3 3 

14 3 1 1 2 1.8 3 

15 1 8 2 2 3.3 4 

16 10 11 10 5 9.0 1 

17 2 4 2 2 2.5 4 

18 2 3 1 1 1.8 4 

 Charge average 7 Total 50 31% 

CCA—5 h pressure 

1 1 3 5 30 9.8 3 

2 4 3 2 5 3.5 4 

3 1 15 1 1 4.5 3 

4 5 2 1 3 2.8 4 

5 2 2 2 10 4.0 3 

6 32 30 2 3 16.8 2 

7 2 2 2 2 2.0 4 

8 33 1 30 1 16.3 2 

9 1 12 1 15 7.3 2 

10 7 20 10 12 12.3 1 

11 12 1 3 2 4.5 3 

12 2 9 10 2 5.8 2 

13 2 2 2 5 2.8 4 

14 24 2 2 5 8.3 3 

15 10 20 37 3 17.5 1 

16 21 5 28 40 23.5 1 

17 20 23 1 2 11.5 2 

18 10 1 8 1 5.0 2 

 Charge average 9 Total 46 36% 

Copper naphthenate—5 h pressure 

1 40 31 30 20 30.3 0 

2 23 20 25 24 23.0 0 

3 10 10 8 30 14.5 1 

4 10 30 5 24 17.3 1 

5 10 11 13 15 12.3 0 

6 30 35 35 32 33.0 0 

7 10 22 8 12 13.0 1 

8 30 12 2 10 13.5 1 

9 12 25 18 20 18.8 0 

10 18 20 19 21 19.5 0 

11 18 17 20 15 17.5 0 

12 12 20 35 15 20.5 0 

13 28 28 28 28 28.0 0 

14 30 35 28 29 30.5 0 

15 30 35 20 29 28.5 0 

16 29 27 20 18 23.5 0 

17 20 21 25 30 24.0 0 

18 30 38 2 12 20.5 1 

 Charge average 22 Total 5 93% 

a

Based on minimum of 9 mm penetration for round posts of western species.
4 

Conclusions 

Although the small-diameter grand fir evaluated in this study 

does not appear to be readily treated with CCA, it does 

appear to be treatable with copper naphthenate in #2 fuel oil. 

Penetration of copper naphthenate exceeded that specified 

by AWPA standards in over 90% of the measurements. 

ACZA has also been demonstrated to be a viable treatment 

option for grand fir round stock. The erratic nature of the 

penetration in the posts in this study warrants further consideration. Some posts that might have passed penetration 

inspection based on removal of a single increment core had 

significant 

gaps in penetration in other portions of the sapwood. On the 

other hand, most posts evaluated in this study had grown 

very slowly and may represent somewhat of a worst-case 

scenario. The results indicate that treatability is affected by 

growing conditions. It is possible that grand fir grown under 

more favorable conditions than those in this study may be 

treated more readily. 

Literature Cited 

AWPA. 2001. Book of Standards. Standard C5, Posts. 

Granbury, TX: American Wood Preservers’ Association. 

Kumar, S.; Morrell, J.J. 1989. Penetration and absorption 

of different CCA compositions in six western conifers. 

Forest Products Journal. 39(10): 19–24. 

Kumar, S.; Morrell, J.J. 1990. Treatment of western 

softwoods with boron amended arsenicals. Forest Products 

Journal. 40(3): 25–29. 

Lebow, S.L.; Morrell, J.J.; Milota, M.R. 1996. Western 

wood species treated with chromated copper arsenate: effect 

of moisture content. Forest Products Journal. 46(2): 67–70. 

Rhatigan, R.; Morrell, J.J. 2000. Unpublished data generated during treatment of Douglas-fir and grand fir posts 

installed at the Oregon State University Post Farm. 

Corvallis, OR: Department of Forest Products, Oregon 

State University.

Figure 2. Examples of pattern of preservative penetration for CCA and copper 

naphthenate treatments. Treated areas appear dark. 

Figure 1. Relationship between growth rate and 

preservative penetration in grand fir posts. 

Cu Naph

CCA- 5 h

CCA- 1 h

0

5

10

15

20

25

30

35

40

2 4 6 8 10 12 14 16 18

Growth rings/cm

Average penetration (mm)

CCA- 1 h CCA- 5 h CuNaph- 5 h

CCA 1h CCA 5 h Cu-Naph 5 h

Post 12

Post 6

Post 3