Resistance of Borax–Copper 

Treated Wood in Aboveground 

Exposure to Attack by Formosan 

Subterranean Termites 

Stan Lebow 

Bessie Woodward 

Douglas Crawford 

William Abbott 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

Research 

Note 

FPL−RN−0295 
Abstract 

The spread of Formosan subterranean termites (FSTs) in the 

southern United States has increased public interest in finding a preservative treatment to protect framing lumber from

termite attack. This study evaluated the use of a borax-based 

preservative to protect wood from FST attack. Southern Pine 

and Douglas-fir specimens were pressure-treated with three 

concentrations of a borax–copper (BC) preservative composed of 93% borax (sodium tetraborate decahydrate) and 

7% technical copper hydroxide. Untreated specimens and 

specimens pressure-treated with disodium octaborate tetrahydrate (DOT) were included for comparison. The specimens were exposed above ground, protected from the 

weather, at an active FST exposure site in Hilo, Hawaii.

Specimens were rated for extent of termite attack after 

6, 12, and 24 months of exposure. The BC treatments provided good protection of Southern Pine, but protection of 

Douglas-fir was variable at all BC retentions evaluated. 

April 2005 

Lebow, Stan; Woodward, Bessie; Crawford, Douglas; Abbott, William.

2005. Resistance of borax–copper treated wood in aboveground 

exposure to attack by Formosan subterranean termites Res. Note FPL-RN0295. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 4 p.

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The variability in protection for Douglas-fir was attributed to 

lower retentions and uneven distribution of preservative 

within the specimens. Average damage ratings of BC-treated 

Southern Pine were slightly better (less damage) than those 

of DOT-treated Southern Pine at equivalent B2O3 retentions, 

suggesting that either the presence of low levels of copper or 

the form of the borate in the BC treatment influenced 

efficacy. The results of this study indicate that borax-based 

treatments can provide adequate protection against FST in

wood species or wood products that allow uniform 

distribution of preservative. 

Keywords: Borax, DOT, copper, Formosan subterranean 

termites, Douglas-fir, Southern Pine, Hawaii
Resistance of Borax–Copper Treated Wood 

in Aboveground Exposure to Attack by 

Formosan Subterranean Termites 

Stan Lebow, Research Forest Products Technologist 

Bessie Woodward, Microbiologist 

Douglas Crawford, Forest Products Technologist (retired) 

Forest Products Laboratory, Madison, Wisconsin 

William Abbott, President 

Pole Maintenance Company, LLC, Columbus, Nebraska 

Introduction 

There is increasing interest in treatment of framing lumber 

and other interior building components to prevent attack by

termites and decay fungi. Borate preservatives are well 

suited for treatment of framing lumber because they are 

odorless and have relatively low human toxicity. The primary disadvantage of borate preservatives, their leachability, 

is also much less of a concern in an indoor application. The 

borate most commonly used for treatment of framing lumber 

is disodium octaborate tetrahydrate (DOT). Numerous researchers have evaluated the efficacy of DOT in protecting 

wood from termite attack (Drysdale 1994, Grace and Yamamoto 1994a, Grace and others 1992, Preston and others 

1996, 1986). Based on these studies, borates have been 

standardized for interior treatments at retentions of 2.8 and 

4.5 kg/m3

 (as B2O3) for areas with native subterranean termites or Formosan subterranean termites (FST), respectively

(AWPA 2003a). The DOT is formed from a mixture of boric

acid and borax and has greater solubility than either borax or

boric acid alone. Borax has also been used as a wood preservative, but not much is known about the concentrations of 

borax needed to prevent attack by FST. On a weight basis, 

borax converts to an equivalent of 37% B2O3, whereas DOT 

converts to an equivalent of 67% B2O3. However, it is unclear whether B2O3 equivalents are an appropriate measure 

of the relative termiticidal properties of borate compounds. It 

is likely that multiple boron species exist within the treated

wood. The purpose of this study was to further investigate 

the use of borates against FST by evaluating a borax-based 

preservative that is currently used for the remedial treatment 

of the groundline area of utility poles (Abbott and others 

2001, Woodward and others 2002). The borax preservative 

selected also contains a small amount of copper as a cobiocide to provide further protection against attack by 

termites, decay, and mold fungi. The possible role of this 

low copper concentration is also discussed. 

Materials and Methods 

Specimen Preparation and Treatment 

Samples (25 by 50 by 178 mm) were cut from clear Southern 

Pine sapwood and Douglas-fir heartwood and conditioned to 

constant weight in a room maintained at 23°C and 65% 

relative humidity. Ten replicates of each wood species were 

treated with one of the following solutions: 

• Borax–copper (BC) (trade name CU-BOR, Copper Care 

Wood Preservatives, Inc., Columbus, Nebraska) with an 

actives composition of 7.2% technical copper hydroxide 

and 92.8% sodium tetraborate decahydrate (10 molar borax). This formulation was evaluated with treatment solutions containing 0.93%, 1.40%, and 2.34% actives 

(Table 1). 

• Disodium octaborate tetrahydrate (DOT), considered 

100% DOT actives. This formulation was evaluated with a 

1.2% solution concentration in Southern Pine and a 1.6% 

solution concentration in Douglas-fir (Table 1). 

Table 1—Composition of treatment solutions

Treatment 

solutiona % 

borax 

% B as 

B2O3

% Cu as 

Cu(OH)2

% Cu as 

CuO 

0.93% BC 0.86 0.29 0.07 0.06 

1.40% BC 1.3 0.47 0.10 0.08 

2.34% BC 2.2 0.80 0.14 0.11 

1.6% DOT

(Douglas-fir) 

— 1.07 — —

1.2% DOT

(Southern Pine) 

— 0.80 — —

a

BC, borax–copper; DOT, disodium octaborate tetrahydrate. 
The BC treatments were conducted with solutions heated to

50°C, whereas the DOT treatments were conducted at ambient temperature. All treatments were conducted using a fullcell pressure process. Following an initial vacuum maintained at –75 kPa (gage pressure) for 30 min, the treatment

solution was introduced into the cylinder. Pressure was then

maintained at 1.03 MPa for 1 hour on the immersed specimens. Each specimen was weighed before and after treatment to determine uptake of preservative. 

Following treatment, the specimens were stacked, covered in 

plastic, for 1 week at room temperature to allow diffusion to 

occur. After the diffusion period, the specimens were airdried and then a 50-mm-long section was cut from each 

specimen. Boron penetration was determined on the freshly

exposed cross section using curcumin and salicylic acid 

indicator solutions prepared in accordance with American 

Wood-Preservers’ Association (AWPA) Standard A3 

(AWPA 2003b). The final specimen size for termite exposure was 25 by 50 by 128 mm. The freshly cut end was not

sealed or treated prior to exposure. 

Exposure and Evaluation 

of Specimens 

The specimens were exposed at a Hilo, Hawaii, test site

provided by Chemical Specialties, Incorporated (Charlotte, 

North Carolina). The site presents a substantial hazard for 

FST attack, as reported in earlier studies (Archer and others 

1991, Preston and others 1986). The method was designed to

simulate sill plates or similar construction conditions where 

dampness or other sources of moisture may exist. In this

method, the specimens were placed horizontally out of direct 

contact with the ground and protected from the weather with

a plywood-topped box enclosure. The specimens were 

placed on decorative open-faced cinder blocks with untreated feeder stakes driven through the vertical holes in the 

blocks and into the soil. Additional feeder stakes were laid

horizontally between the rows of specimens. Each test unit

covered an area of approximately 1 m2

. In this study, two 

test units were needed to accommodate all samples. A visual 

inspection of the specimens was conducted after 6, 12, and 

24 months of exposure using a rating scale (10, 9, 8, 7, 6, 4, 

and 0). The untreated feeder stakes were replaced at each 

inspection to facilitate attack and were completely destroyed

at 12 and 24 months. Weight loss was also determined at the 

conclusion of the test (24 months). At the 6-month inspection, one of the test units had no termite attack because of an 

ant infestation. This unit was moved to another location and 

did sustain FST attack at the 12- and 24-month inspections. 

A comparison of the ratings of similarly treated samples 

exposed in the two test units indicates that there was no 

difference in the amount of attack between the two units

after 24 months of exposure. 

Results and Discussion 

Because of treatability differences, the amount of preservative delivered to the test specimens differed by both wood 

species and type of preservative. Specimens treated with 

DOT experienced greater solution uptake than those treated 

with BC, resulting in higher retentions in the wood 

(Table 2). The greater uptake with the DOT solutions agrees 

with a previous study that compared the treatability of BC 

and DOT across a range of wood species (Lebow and others, 

in press). The uptake of BC was also greater in Southern 

Pine than Douglas-fir, resulting in higher retentions for 

Southern Pine. For the BC treatments, all Douglas-fir borate 

retentions were below AWPA specifications (4.5 kg/m3

 as 

B2O3) for protection of wood against FST (AWPA 2003a). 

In contrast, the average B2O3 retention from DOT treatment

of Douglas-fir was well above the specified level.

Following treatment, a 50-mm section was cut from the 

samples after treatment to assess penetration. The termites 

preferred to enter the samples from that cut end, suggesting 

that the wood in that area was not penetrated with preservative. However, based on the indicator spray, the entire cross 

section of these samples was penetrated with boron for all of 

the BC- and DOT-treated specimens, including Douglas-fir. 

As expected, copper penetration in the BC-treated Douglasfir samples was limited to a shell treatment of 1 to 

2 mm. Copper penetration was much more extensive in the 

BC-treated Southern Pine specimens, although there were 

small unpenetrated areas in some specimens. 

These differences in treatability between wood species are 

reflected in the ratings of termite attack for the BC specimens (Table 2). Some Douglas-fir specimens treated with

BC suffered substantial attack at each BC retention level, 

whereas Southern Pine specimens treated to the highest BC 

retention (4.8 kg/m3

) were well protected, and specimens 

treated with an intermediate B2O3 retention (2.7 kg/m3

) 

suffered slight attack. The variability in Douglas-fir treatment with BC resulted in a range of retentions (Fig. 1). 

Across this range, there appeared to be little correlation

between B2O3 retention and termite attack for the BC-treated

specimens (Fig. 1). This suggests that deficiencies in both 

penetration and retention may have contributed to attack of 

the BC-treated Douglas-fir specimens. Although the Douglas-fir specimens appeared fully penetrated with boron, the 

indicator solution indicates only the presence, not the concentration, of boron. The specimens probably had a gradient

of boron concentration across the cross section. It also appears that Southern Pine specimens treated to similar BC 

retentions were better protected than their Douglas-fir 

counterparts. None of the Southern Pine specimens was 

rated below a 6 regardless of B2O3 retention. Copper may

have also contributed to the protection of the BC-treated 

Southern Pine specimens, as ratings for these specimens 

2 
Table 2—Average preservative retention, termite attack ratings, and weight loss for 

Douglas-fir (DF) and Southern Pine (SP) specimens treated with borax–copper (BC) 

and disodium octaborate tetrahydrate (DOT) solutions

Retention 

(kg/m3

) 

Ratings for termite attack, average 

Wood (minimum) 

species 

Treatment 

solution B2O3 CuO 6 months 12 months 24 months

% weight 

loss, average 

(maximum) 

DF 0.9% BC 1.60 0.26 9.7 (8) 8.7 (6) 7.2 (4) 17 (41) 

DF 1.4% BC 2.24 0.35 9.7 (8) 8.9 (7) 5.6 (0) 26 (65) 

DF 2.3% BC 3.04 0.48 10.0 (10) 9.0 (7) 5.1 (0) 25 (48) 

DF 1.6% DOT — — 9.6 (8) 8.9 (7) 8.3 (7) 5 (12) 

DF None — — 9.0 (0) 7.6 (0) 0.4 (0) 71 (>90) 

SP 0.9% BC 2.08 0.34 10.0 (10) 9.0 (8) 7.8 (7) 7 (24) 

SP 1.4% BC 2.72 0.43 9.8 (9) 9.6 (8) 8.5 (6) 9 (34) 

SP 2.3% BC 4.80 0.77 10.0 (10) 9.8 (9) 9.6 (8) 4 (12) 

SP 1.2% DOT 5.12 — 10.0 (10) 9.2 (8) 8.5 (7) 3 (14) 

SP None — — 8.0 (0) 6.4 (0) 0.0 (0) >90 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

0 2 4 6 8

Specimen B2O3 retention (kg/m3

)

T

ermite r

ating (24 months)

BC Doug-fir

BC S. Pine

DOT S. Pine

DOT Doug-fir

Figure 1—Relationship between 24-month termite attack rating and B2O3 retention for 

individual specimens. 

were slightly higher than those treated with DOT to similar 

B2O3 retentions. It is also possible that the form of boron 

applied (borax or DOT) affected the efficacy of the boron. 

In contrast to the BC treatment, performance of DOT-treated 

specimens was similar for Southern Pine and Douglas-fir 

(Table 2; Fig. 1). Some attack was observed in both wood 

species although the B2O3 retention was above the 4.5 kg/m3

level specified in AWPA Standards. The attack was readily 

visible but typically shallow, as indicated by the relatively 

low weight loss of these samples (Table 2). Previous researchers have also noted that wood treated with DOT to

relatively high retentions may sustain some attack by FST 

(Grace and others 1992, 2001, Grace and Yamamoto 1994a, 

Preston and others 1996). Grace and Yamamoto (1994b) 

attributed this attack to localized variations in DOT retention

within the wood substrate. This explanation is in agreement

with the variable protection provided by BC treatment of 

Douglas-fir. 

3
Conclusions 

The BC treatments provided good protection of Southern 

Pine at B2O3 retentions slightly above that required by

AWPA standards. However, protection of Douglas-fir was 

variable at all BC retentions evaluated, probably because of 

the combination of low retentions and uneven distribution of 

boron within the treated wood. Uptake of DOT was greater 

and less variable than that of BC in both the Douglas-fir and 

Southern Pine specimens. As has been reported previously, 

DOT-treated specimens suffered slight termite attack even at 

retentions above that specified in AWPA standards. Ratings 

of BC-treated Southern Pine were slightly better than those 

of DOT-treated Southern Pine, suggesting that either the 

presence of low levels of copper or the form of the borate 

positively influenced efficacy. The results of this study 

indicate that BC treatments can provide adequate protection 

against FST in wood species or wood products that allow 

uniform distribution of preservative. 

Acknowledgments 

The authors thank the researchers from Chemical Specialties 

Incorporated for allowing use of their test site and for their 

assistance in exposing and rating the specimens. 

Literature Cited 

Abbott, W.; Crawford, D.M.; West, M. 2001. Permanence 

of a borax-copper hydroxide remedial preservative when 

applied to unseasoned pine posts. In: Proceedings, American 

Wood-Preservers Association. 97:190–193. 

Archer, K.J.; Fowlie, D.A.; Preston A.F.; Walcheski, P.J. 

1991. A termite field test with diffusion treated lumber. 

IRG/WP/3648. Stockholm, Sweden: International Research 

Group. 

AWPA. 2003a. Book of standards. Commodity specification 

A—Sawn products. Selma, AL: American Wood-Preservers’ 

Association. 

AWPA. 2003b. Book of standards. Standard A3–00. 

Standard methods for determining penetration of preservatives and fire retardants. Selma, AL: American Wood 

Preservers’ Association. 

Drysdale, J.A. 1994. Boron treatments for the preservation 

of wood—A review of efficacy data for fungi and termites. 

IRG/WP/94–30037. Stockholm, Sweden: International

Research Group. 

Grace, J.K.; Yamamoto, R.T. 1994a. Repeated exposure 

of borate-treated Douglas-fir lumber to Formosan subterranean termites in an accelerated field test. Forest Products 

Journal. 44(1):65–67. 

Grace, J.K.; Yamamoto, R.T. 1994b. Natural resistance of 

Alaska-cedar, redwood, and teak to Formosan subterranean 

termites. Forest Products Journal. 44(3):41–45. 

Grace, J.K.; Yamamoto, R.T.; Tamashiro, M. 1992. 

Resistance of borate-treated Douglas-fir to the Formosan 

subterranean termite. Forest Products Journal. 42(2):61–65. 

Grace, J.K; Oshiro, R.J.; Byrne, T.; Morris, P.I.; 

Tsunoda, K. 2001. Performance of borate-treated lumber in 

a four-year, above-ground termite field test in Hawaii.

IRG/WP 01–30265. Stockholm, Sweden: International

Research Group on Wood Preservation. 

Lebow, S.T.; Hatfield, C.A.; Abbott, W. [In press]. 

Treatability of SPF framing lumber with CCA and borate 

preservatives. Wood and Fiber Science. 

Preston, A.F; McKaig, P.A.; Walcheski, P.J. 1986. 

Termite resistance of treated wood in an above ground field 

test. IRG/WP/1300. Stockholm, Sweden: International Research Group. 

Preston, A.F.; Jin, L.; Archer, K.J. 1996. Testing treated 

wood for protection against termite attack in buildings. In:

Proceedings, American Wood Preservers’ Association. 

92:205–220. 

Woodward, B.; Abbott, W.; West, M. 2002. Retreatment 

of spent creosote-treated wood with copper hydroxide and 

sodium tetraborate. In: Proceedings, American WoodPreservers’ Association. 98:58–61. 

4