Evaluation of Nonpressure 

Wood Preservatives for 

Military Applications

Stan T. Lebow

Samuel L. Zelinka

Rachel A. Arango

Bessie M. Woodward

Patricia K. Lebow

Katie M. Ohno

Nathaniel P. Chotlos

United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

Research Paper

FPL–RP–693

October

2017
Abstract

Zinc naphthenate (ZnN) has been widely used for dip 

treatment of Department of Defense wood packing materials 

but is no longer available. Research was conducted to 

evaluate the preservative efficacy and corrosiveness of U.S. 

Environmental Protection Agency (EPA) registered 

alternatives to ZnN. Efficacy of “green” preservatives 

(defined here as not containing pesticides that require EPA 

registration) was also evaluated. Most of the EPA-registered 

preservatives evaluated provided decay and termite 

protection similar to or greater than that of ZnN. Four of the 

formulations provided protection equivalent to or greater 

than that of ZnN against termites and all decay fungi 

evaluated. The registered formulations tended to be more 

effective than ZnN in preventing termite feeding on 

Southern Pine, but some were less effective than ZnN in 

protecting yellow-poplar from termites. However, the 

“green” preservatives were not effective in preventing decay 

or termite attack. Corrosion testing revealed that all but one 

of the registered formulations were more corrosive than 

ZnN. The results of the laboratory fungal, termite, and 

corrosion testing were used to develop a protection index 

with recommended applications for the formulations 

evaluated.

Keywords: wood preservatives, nonpressure, dip, decay, 

termites, corrosion, Department of Defense, wood packing 

materials

October 2017

Lebow, Stan T.; Zelinka, Samual L.; Arango, Rachel A.; Woodward, 

Bessie M.; Lebow, Patricia K.; Ohno, Katie M. 2017. Evaluation of 

nonpressure wood preservatives for military applications. Research Paper 

FPL–RP–693. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 30 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726-2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin.

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

Contents

Introduction........................................................................ 1

Current Treatment Specifications....................................... 1

Characteristics of Formulations Currently 

in Military Specifications................................................... 2

Considerations for Alternative Preservatives..................... 3

Materials and Methods....................................................... 4

Results and Discussion, EPA-Registered Preservatives... 11

Results and Discussion, Green Preservatives................... 21

Summary and Recommended Applications ..................... 25

Acknowledgments............................................................ 27

Literature Cited ................................................................ 27

Appendix—Protection Index: Methods and Criteria 

for Evaluating Candidate Preservatives ........................... 29

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Introduction

The U.S. Army uses wood for construction of containers 

(such as ammunition boxes) and shipping materials (such as 

pallets). These wood packaging materials (WPMs) are 

expected to have a useful life of up to 20 years, and 

although the majority of their service will be indoors, there 

may be extended periods of outdoor exposure. The wood 

may also be exposed in climates that present a severe risk 

for both insect and fungal attack. To protect the wood from 

biodegradation, current Department of Defense (DOD) 

specifications stipulate that the assembled wood products be 

dip-treated with a wood preservative (Fig. 1). A thorough 

evaluation of the efficacy of preservatives in protecting 

ammunition boxes was conducted by the USDA Forest 

Service, Forest Products Laboratory (FPL), and U.S. Army 

Armaments Research and Development personnel in the 

1980s (DeGroot and Stroukoff 1986). That study indicated 

that water-based zinc naphthenate (ZnN), copper 

naphthenate (CuN), and copper-8-quinolinolate (Cu8)

would be effective for treatment of ammunition boxes, and 

these three preservatives were incorporated into DOD 

specifications. Of these, the most commonly used

preservative has been ZnN. However, ZnN no longer has 

U.S. Environmental Protection Agency (EPA) registration 

for use as a wood preservative and will not be available after

existing stocks are depleted. Also, changes have occurred in 

the available formulations of CuN and Cu8, and new types 

of preservatives have become available since the study by 

DeGroot and Stroukoff (1986). To adapt to these changes 

and ensure future availability, U.S. Army Armament 

Research Development and Engineering Center (ARDEC)

and FPL personnel conducted research to evaluate the 

efficacy of potential preservatives for use in protecting

WPMs.

Current Treatment Specifications

Preservative treatment of WPMs is covered in multiple 

specifications. Two commonly used military specifications 

are MIL-DTL-2427H (AR) (September 2007) for nailed 

wood boxes and MIL-DTL-46506E (August 2009) for wirebound wood boxes. These specifications state that the 

boxes, or their finished wood parts, shall be completely 

immersed for a minimum of 1 min in the preservative 

solution. The preservative solutions listed are

• PQ56 reduced with water down to 1.8% Cu8 (this is an 

older version of Cu8 that is no longer being produced).

• An emulsion of wood preservative M-GARD W550 

(ZnN) reduced with water down to 3% zinc as metal.

• An emulsion of M-GARD W510 (CuN) reduced with 

water to 2% copper as metal (this is an older version of 

CuN that is no longer being produced).

• A solution of Cunapsol 5 (CuN) reduced with water to 

2% copper as metal (this is an older version of CuN that 

is no longer being produced).

The specification also requires that all interior and exterior 

surfaces (when finished wood parts are dipped) be 

completely inundated with preservative. Immediately 

following the dip treatment, the wood products are to be 

Evaluation of Nonpressure Wood 

Preservatives for Military Applications

Stan T. Lebow, Research Forest Products Technologist

Samuel L. Zelinka, Supervisory Research Engineer

Rachel A. Arango, Research Entomologist

Bessie M. Woodward, Microbiologist (retired)

Patricia K. Lebow, Research Mathematical Statistician

Katie M. Ohno, Biologist

USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin

Nathaniel P. Chotlos, Student

University of Wisconsin-Madison, Department of Forest and Wildlife Ecology, Madison, Wisconsin

Figure 1. Nailed ammunition boxes are one example of 

durable wood packaging materials that are dip-treated with 

preservative.
Research Paper FPL–RP–693

2

drained for at least 5 min and then air-dried for at least 24 h 

while allowing full air circulation around all surfaces.

Accelerated drying in an oven or kiln is permitted providing 

oven or kiln temperatures do not exceed 71 °C. The treated 

boxes must be dried to a maximum moisture content of 18% 

prior to shipment. Verification of preservative treatment is 

accomplished by applying an indicator solution that 

produces a characteristic color if the applicable preservative 

is present.

A range of softwood and hardwood species are permitted 

under these specifications; all must be dried to a maximum

moisture content of 19%. Typical boxes are constructed of 

solid wood or plywood panels with additional cleats added 

on the ends and lid to improve stiffness and connection 

strength. The thickness of these members is typically 13 to 

18 mm, although greater thicknesses may also be used.

Nail, wire, or staple fasteners are permitted, and flat or wire 

steel strapping may also be applied. The specifications 

typically call for metal components to be protected with a 

zinc coating to lessen corrosion, although the thickness of 

the zinc coating is often not specified.

Characteristics of Formulations 

Currently in Military Specifications

Various forms of CuN, Cu8, and ZnN have been used as 

preservatives for decades, although these previous 

formulations may not be identical to those listed in current 

military specifications.

Water-Based Copper Naphthenate

CuN has been used as a wood preservative since the 1940s, 

although not as widely as creosote, chromated copper 

arsenate (CCA), or pentachlorophenol. It is an 

organometallic compound formed as a reaction product of 

copper salts and petroleum-derived naphthenic acids. In 

recent years, use of CuN has increased for pressure

treatment of poles, glue-laminated beams, and railroad ties.

CuN has been primarily used as an oil-based formulation,

but a water-based formulation containing ethanolamine has 

also been standardized as Standard P34 by the American 

Wood Protection Association (AWPA) for pressure 

treatment (AWPA 2017). Standardized retentions range 

from 1.12 kg/m3 for above-ground use to 1.76 kg/m3 for 

ground-contact applications (retentions expressed as 

elemental copper). FPL compared the durability of stakes 

treated with oil- and water-based formulations of CuN and 

found that the oil-based formulations were more durable at 

lower concentrations. However, at the highest concentration 

evaluated (1.2% copper), both formulations were highly 

effective. DeGroot and Stroukoff (1988) also found that 2% 

copper formulations of oil- or water-based CuN were highly 

effective in protecting ammunition boxes from decay, even 

in jungle exposure in Panama.

Water-Based Copper-8-quinolinolate

Cu8 is an organometallic preservative comprised of 10% 

Cu8 and 10% nickel-2-ethylhexoate. It is characterized by 

its low mammalian toxicity and is permitted by the U.S. 

Food and Drug Administration for treatment of wood used 

in direct contact with foodstuffs. The treated wood has a 

greenish brown color and little or no odor. It can be 

dissolved in a range of hydrocarbon solvents and has often

been used and evaluated as an oil-based treatment (Lebow 

and others 2014). However, it can be formulated for use in 

water, and the water-based form is used commercially for 

dip treatment and as a component of antisapstain 

preservatives.

Durability evaluations of water-based Cu8 have produced 

somewhat conflicting results. FPL researchers evaluated the 

durability of stakes treated with water-based Cu8 in both 

19- by 19-mm and 38- by 89-mm stake sizes. The 19- by 

19-mm stakes treated to retentions of 5.44, 15.04, 20.80,

and 29.44 kg/m3 survived an average of 3.3, 6.2, 7.3, and

8.6 years, respectively. This relatively poor durability 

contrasts with that of the larger stakes treated to 17.9 kg/m3

,

which had only 40% failures after 17 years. Highley (1993) 

evaluated the ability of a 5% water-based Cu8 brush 

application to protect cross-brace specimens exposed above

ground in Wisconsin and Mississippi. In this test, two 

treated pieces of wood, 19 by 76 by 153 mm long, were 

nailed together at their centers to form a cross-brace test 

unit. The design of the cross-brace unit was intended to 

allow trapping of rainwater between side-grain surfaces.

However, this is not a standardized test method and is not 

especially severe because moisture is not trapped in the endgrain. Water-based Cu8 did not perform particularly well in 

this test, with decay observed within 7 years in pine 

specimens and within 2 years in maple specimens exposed 

in Mississippi (Table 1). In contrast, pine specimens 

brushed with 1% water-based copper or ZnN had no decay 

after 9 years and maple specimens resisted decay for 

7 years. Mitchoff and Morrell (1988) evaluated the ability of 

water-based Cu8, ZnN, and other preservatives to protect 

red alder using AWPA Standard E10 soil-block tests

(AWPA 2017). They found that water-based Cu8 was less 

effective than other preservatives tested in protecting red 

alder. However, DeGroot and Stroukoff (1986) found that at 

1.2%, water-based Cu8 solution provided protection to 

ammunition boxes that was nearly equivalent to that of 

water-based ZnN or CuN. They also noted that a Cu8 

emulsion did not protect as well, suggesting that the efficacy 

of Cu8 may be dependent on how the Cu8 is stabilized in 

the treatment solution. This formulation dependence may 

explain the range of results presented by previous 

researchers.
Evaluation of Nonpressure Wood Preservatives for Military Applications

3

Zinc Naphthenate

ZnN is formed as a reaction product of zinc salts and 

derived naphthenic acids. Until recently, ZnN was used 

extensively as a component in over-the-counter wood 

preservative products. As with CuN, it can be formulated as 

either a solvent- or water-based preservative. Unlike CuN, 

ZnN imparts little color to the wood. Zinc is not as effective 

a fungicide as copper (Barnes and others 2004), and ZnN is 

not used as a stand-alone preservative for exposed structural 

members, nor is it standardized for pressure treatment.

Barnes and others (2004) compared the durability of stakes 

treated with a range of retentions of water-based CuN or 

ZnN and found that approximately three times more zinc 

was needed to provide protection equivalent to copper.

However, ZnN does have some preservative efficacy, 

especially in above-ground applications. A comparison of 

above-ground specimens exposed in Mississippi found that 

brush-on treatments of water-based ZnN were only slightly 

less effective than CuN after 9 years of exposure (Table 1) 

(Highly 1993). Dip treatments with a 3% (as zinc) 

formulation also protected pine and hemlock L-joints for 

11 years in western Oregon (Morrell and others 1999).

DeGroot and Stroukoff (1986) also reported that dips in a 

3% (as zinc) formulation protected ammunition boxes 

nearly as well as CuN after 36 months of jungle exposure.

Interestingly, there was no benefit from increasing dip time 

from 1 to 3 min. Water-based ZnN also provided good 

protection for ammunition boxes exposed in an open field in 

Panama, with 100% of the panels and cleats remaining 

serviceable after 36 months of exposure. An advantage of 

ZnN, relative to copper-containing water-based 

preservatives, is lower corrosiveness to metal fasteners.

However, ZnN is currently not registered for pesticide use, 

and it does not appear likely that it will be registered in the 

near future.

Considerations for Alternative 

Preservatives

Preservatives have a range of properties that may make 

them more or less suitable for dip treatment of WPMs. 

Clearly, efficacy in preventing degradation by decay fungi 

and termites is critical, but factors such as regulatory status, 

allowable methods of application, handling characteristics,

and simplicity of mixing and use must also be considered.

Data on efficacy against decay fungi and termites are

available for many types of preservative formulations, 

although the bulk of this information was developed with 

pressure-treated wood. Pressure-treated wood typically has 

deeper and more uniform penetration and retention than 

wood treated by nonpressure processes (although extended 

soaks can create similar treatment quality in some species).

Dip- or brush-treated wood can have a higher surface 

concentration of preservative. However, its location near the 

wood surface makes the preservative more vulnerable to 

depletion, and even small drying checks expose untreated 

wood. As a result, the durability of pressure-treated wood is 

often substantially greater than that of wood treated by 

nonpressure means.

Conventional wood preservatives contain antimicrobial 

pesticides (such as copper) that require registration and 

labeling with EPA. Some preservatives developed for 

pressure treatment have not been labeled for dip treatment 

application and/or may be labeled for concentrations below 

that needed for dip treatment. In some cases, the properties 

of a preservative, such as odor or volatility, may make them 

less amenable for use in a dip treatment facility.

Corrosiveness to metal fasteners may also be a concern 

because WPMs are typically dipped after assembly.

Nonconventional wood preservatives were also considered 

in this study. As part of a broader effort to evaluate green 

packaging materials, the U.S. Army is seeking information 

on green wood preservatives that might be used for 

protection of WPMs. In this case, “green” is defined as 

preservatives that do not contain pesticides requiring EPA 

registration. The basis for this classification is somewhat 

unclear because the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) defines a pesticide as “any 

substance or mixture of substances intended for preventing, 

destroying, repelling, or mitigating any pest” and because

any such substance must be registered unless it was

otherwise specifically exempted. However, there are a 

number of commercial products that appear to claim wood 

preservative efficacy but do not contain EPA-registered 

pesticides. Because these products are not EPA-registered, 

they do not necessarily identify or quantify their ingredients.

Thus, it can be difficult to understand their mechanism of 

action or gauge their potential efficacy. Examples include 

products derived from wood extracts (for example, cedar 

oil) and minerals (for example, silicates) and those that

Table 1—Durability of brush-treated cross-brace 

units exposed above ground in southern 

Mississippi (data from Highley (1993))

Preservative

(waterborne)

Solution

conc. 

(%)

Years to visual decay by 

wood speciesa

Pine Maple Oak

Copper-8-

quinolinolate

1 7 2 8

5 7 2 8

Copper 

naphthenate

1 9+ 6 8

3 9+ 7 9+

8 9+ 9+ 9+

Zinc 

naphthenate

1 9+ 5 6

3 9+ 5 6

8 9+ 6 7

a

Some specimens did not develop visual decay during the test. Test 

durations were either 9, 10, or 11 years.
Research Paper FPL–RP–693

4

claim to act by physically blocking movement of water or 

deterioration organisms into the wood (for example, water 

repellents or sealants).

The potential use of extractives from naturally durable wood 

species as wood preservatives has been studied since at least 

the early 1940s (Rennerfelt 1948), and research continues 

today (Kirker and others 2013a). Although this research 

shows that extracts such as cedar oil do have antifungal 

properties in agar plate testing (Du and others 2009), their 

efficacy in protecting wood of nondurable wood species is 

less clear. Two studies have indicated that wood treated 

with cedar oil extracts has only slight improvement in decay 

resistance but may have substantially increased resistance to 

termite attack (Eller and others 2010, Kirker and others

2013b). Earlier research at FPL (unpublished) found that 

cedar extracts at concentrations up to 2% provided no 

benefit in preventing attack by two types of decay fungi. 

However, research with essential oil extracts from a range 

of plant species indicated that essential oils can be 

efficacious against decay fungi if used at high 

concentrations (Yang and Clausen 2007). Generally, it 

appears possible that extractives from naturally durable 

species may be capable of protecting nondurable woods, but 

the expense of concentrations required may limit practical 

implementation.

Various forms of silicates have drawn considerable interest 

as pesticide-free wood treatments. Research efforts on 

organosilicons summarized in papers by Mai and Miltz 

(2004a, 2004b) and Weigenand and others (2009) indicated

that although certain formulations provide some decay 

resistance, silicon was generally insufficient without 

substantial loadings, modification with amino groups, or the 

addition of a fungicide such as boron. Other common

minerals have also been proposed for wood protection. For 

example, formulations of iron and aluminum have been 

evaluated at FPL. Those evaluations indicated that these 

metals have relatively little efficacy against decay fungi or 

termites when wood is placed into contact with the ground. 

They do, however, impart some increase in durability for 

wood exposed above ground.

Moisture barriers and coatings have also been considered as 

potential mechanisms of wood protection. On larger 

material, water-proof coatings have generally not been as 

effective as wood preservatives because the coating is 

typically breached either through coating decomposition or 

from cracks that develop as wood shrinks and swells (Feist 

1988). However, they can provide some level of protection 

for wood above ground as long as the coating is intact. One 

study found that painting alone provided some protection 

for Douglas-fir specimens exposed above ground but was 

less effective for pine specimens (Highley and Scheffer 

1998). Coatings would be expected to be most effective on 

wood species and products with minimal shrinkage and low 

water permeability (such as Douglas-fir) and on wood 

products with smaller dimensions that undergo less shrink

and swell with time. With sufficient penetration, waterrepellent treatments can also be effective. Pressure treatment 

with paraffin wax to a loading of 416 kg/m3 increased the 

average life of stakes exposed in Mississippi from 2.3 

(untreated) to 18.4 years (Woodward and others 2011).

Based on these considerations, nine EPA-registered 

preservative formulations and six green preservative 

formulations were evaluated for resistance to fungal decay 

and feeding by subterranean termites. EPA-registered 

preservatives were also used in corrosion testing. With the 

exception of one green preservative, only water-based

formulations were evaluated to allow compatibility with 

existing treatment facilities and use practices.

Materials and Methods

EPA-Registered Formulations Evaluated

All but one of the evaluated alternative formulations 

contained copper as a key active ingredient (Table 2). 

Table 2—Preservatives and concentrations evaluated (only the higher concentrations were evaluated in 

corrosion testing)

Preservative Description

Key active ingredient 

(% actives)

Dip time

(min)

CuC Copper-carboxylic acid (100%) 1% and 2% as copper 1

AzI Azolea (95%), imidacloprid (5%) 0.5%b or 1.05% total actives 1 and 3

pCuA-1 Particulate copper (96%), azolea (4%) 1% and 2% as copper 1

pCuA-2 Particulate copper (96%), azolea (4%) 1% and 2% as copper 1

sCuA Soluble copper (96%), azolea (4%) 1% and 2% as copper 1

Cu8-1 Copper-8-quinolinolate (100%) 1.2% as Cu8-quin 1 and 3

1.8%c as Cu8-quin 1

Cu8-2 Copper-8-quinolinolate (100%) 1.2% and 1.8%c as Cu8-quin 1

CuN Copper naphthenate (100%) 1% and 2%c as copper 1

ZnN Zinc naphthenate (100%) 2.9%c as zinc 1

a

Tebuconazole or equal parts tebuconazole and propiconazole. b

0.5% AzI concentration evaluated in green preservative study and limited to the 1-min dip time. c

Concentrations required in current military specifications for similar formulations. ZnN is specified at 3% zinc.
Evaluation of Nonpressure Wood Preservatives for Military Applications

5

Copper has been used in wood preservatives for centuries 

and remains a common component in current formulations. 

It is effective against most types of decay fungi as well as 

major insect pests. However, certain types of decay fungi 

have been found to be copper-tolerant and can sporadically 

cause rapid damage and even structural failure of coppertreated wood. Thus, commercial copper-based preservatives 

typically include a co-biocide (for example, triazoles, 

naphthenic acids, quinolinolate) to provide additional 

protection. In two of the test formulations, mechanically 

ground particulate copper was dispersed or suspended in the 

formulation (particulate copper azole (pCuA-1 and pCuA2)). This type of formulation, often referred to as micronized 

copper, is commonly used for pressure treatment of lumber 

in the United States. Copper particle sizes generally range 

between 1 and 25,000 nm, with the majority less than

1,000 nm. Polymeric dispersants are used to improve the 

uniformity and stability of the treatment solution (Freeman 

and McIntyre 2008). A formulation with a similar 

composition of active ingredients but with copper 

solubilized in ethanolamine (sCuA) was also evaluated. All 

three formulations also included one or both of the triazoles,

tebuconazole, and/or propiconazole, which are agricultural 

fungicides that have been incorporated into some wood 

preservative formulations. An additional copper formulation 

contained copper solubilized in ethanolamine as well as a 

carboxylic acid (CuC). The one formulation evaluated that 

did not contain copper instead contained a combination of 

azoles and imidacloprid (AzI). The active concentrations of 

the formulations evaluated were relatively high compared 

with those used for other applications of the same 

preservatives. This reflects the concentrations shown to be 

effective for ZnN, Cu8, and CuN in earlier testing (DeGroot 

and Stroukoff 1986).

Green Preservatives Evaluated

Green preservatives were selected based on a combination 

of availability and possible mode of action. For the purposes 

of this study, the products will be described based on their 

characteristics or proposed method of action rather than by 

use of commercial trade names. With the exception of the 

cedar oil extract, only water-based products were considered 

to correspond to current use practices for WPM dip 

treatment.

Cedar Oil–Organosilicon

Cedar oil–organosilicon (Cedar) is a solvent-based product 

that is marketed as a wood preservative and stabilizer. It

functions through a combination of eastern redcedar oil and 

organosilicon polymerization. Efficacy is claimed against 

cellulose-consuming insects and fungal decay organisms. 

The method of action is proposed by the manufacturer to be 

encapsulation of antimicrobial and termiticidal ingredients 

(presumably the cedar oil) within the cell wall structure by 

silicon molecules. The manufacturer provides instructions 

for application by dipping, hot and cold bath immersion, or 

spraying. During discussions, the manufacturer 

recommended that the product be applied using two dips 

with a short drying period between dips. We duplicated this 

process for an additional set of specimens in this trial.

Silica Gel Wood Stabilizer

Silica gel wood stabilizer (LiqSil) is a water-based product 

that claims to function as a silica gel that hardens with time 

into a glass-like consistency. Given this description, it is 

likely that this product contains sodium silicates. The 

product claims to be a wood stabilizer–hardener that keeps 

the moisture content below that needed for attack by decay 

fungi. The product does not appear to make claims of 

efficacy against termites or other insects. Recommended 

application is two brush coats with a drying interval of at 

least 6 to 12 h between coats. This study evaluated the two 

brush coats application as well as a 1-min dip treatment.

Natural Minerals 1

The manufacturer of this natural mineral (Mineral-1) 

emphasizes its use as a stain but also claims that the product 

protects against mold, rot, and fungi. No claims are made 

regarding termites. Little information is provided about its 

ingredients or method of action other than a statement that it 

is composed of natural substances from minerals. However, 

in one area of the website, it does note that a key component 

is silica that solidifies to form a glass-like moisture barrier. 

Thus, it is likely that the product contains sodium silicate. It 

is sold as a packet of granules, which are then mixed with 

water for application by brush, sprayer, or roller. The 

information provided by the manufacturer indicates that 

only one application is needed. This product was applied by 

dipping in this study.

Natural Minerals 2

The manufacturers of this natural mineral (Mineral-2) claim 

that it is effective against moss, mold, wet rot, dry rot, and 

fungi. A mechanism of protection is not provided by the 

manufacturer other than to state it is based on natural 

materials and penetrates into wood fibers, altering the wood 

structure at a molecular level. As with Mineral-1, the 

product is sold as a packet of granules, which is then mixed 

with water for application. Given the similarity in 

description to Mineral-1, it is likely that this product also 

contains sodium silicate. Manufacturer guidelines state that 

it can be applied by dipping and that only one application is 

required.

Polymer Seal

The polymer seal (Polymer) provides efficacy by forming a 

waterproof seal on the exterior of the wood. It contains an 

undisclosed proprietary polymer (99% concentration) that is 

a white emulsion, dispersible in water. However, it is 

applied full strength, without dilution. Although marketed 
Research Paper FPL–RP–693

6

primarily as a water-proofer and sealer for fencing, siding, 

posts, and furniture, it also claims to protect against decay, 

rot, and pests. The recommended method of application is 

by sprayer, but in this study, it was applied only by dipping.

Nonpreservative Deck Water Repellent

Some of the products evaluated in this study claim efficacy 

in part because they create a barrier to water intrusion on the 

wood surface. The laboratory fungal and termite tests used 

in this study use small test specimens with a relatively high 

surface area to volume ratio. Thus, specimens are 

completely encapsulated with the test formulations during 

dip treatment. This raised the question of whether these 

standard methods are a sufficiently rigorous test of the 

water-repellent surface treatments. To address this concern,

we evaluated an example of a water-based commercial 

water-repellent deck treatment (Deck WR) that does not 

make any claims of efficacy against decay fungi and 

termites. The product is manufactured and marketed by one 

of the leading suppliers of deck finishes. It is intended to be 

applied by brush or roller but was applied by dip treatment 

in this study.

Zinc Naphthenate

The same water-based ZnN (3% Zn) formulation used in the 

evaluation of EPA-registered preservatives was included as 

a positive control in the green preservative evaluation.

Azoles–Imidacloprid

This formulation was included in the evaluation of EPAregistered preservatives and appeared to be highly effective

(Lebow and others 2015). It was included here as a positive 

control but was diluted to a lower (0.5%) concentration.

Soil-Block Decay Tests

The soil-block (also referred to as soil bottle) method is the 

most common laboratory test used to evaluate the efficacy 

of wood preservatives against wood decay fungi. This test 

exposes preservative-treated blocks (and untreated controls) 

to specific, known decay fungi under conditions favorable 

for their growth (Fig. 2). The effectiveness of the 

preservative is based on the amount of weight loss in the 

test block compared with untreated controls. The method 

used in this study was AWPA Standard E10 (AWPA 2017).

Selection of Wood and Fungal Species

Two wood species (one softwood and one hardwood) were 

evaluated in this study. Southern Pine (Pinus spp.) was 

selected because it is a widely used softwood with a large, 

nondurable sapwood zone. Yellow-poplar (Liriodendron 

tulipifera) was selected because it is a common, nondurable 

hardwood that grows across a large geographical area. It 

was also selected because it was used in the earlier 

ammunition box study by DeGroot and Stroukoff (1986). 

Soil bottles with feeder strips were inoculated with one of 

five decay fungi selected for use in this study in accordance 

with AWPA Standard E10 (AWPA 2017). Brown-rot fungi 

(Gloeophyllum trabeum (Pers. ex Fr.) Murr.; Mad617 and

Postia placenta (Fr.) M. Lars. & Lomb.; Mad698) were 

used to evaluate the Southern Pine specimens, and white-rot 

fungi (Trametes versicolor (L. ex Fr.) Pilat; Mad697 and 

Irpex lacteus (Fries)(Schw.); Mad517) were used to 

evaluate the yellow-poplar specimens. The soft-rot fungus 

Chaetomium globosum (Kunze et Fr.) was evaluated against 

both Southern Pine and yellow-poplar specimens but only 

for testing of EPA-registered preservatives. The soft-rot 

method was modified with use of a filter paper feeder strip 

and burial of the test block in moist, sterile vermiculite. 

These fungal species were selected because they are among 

those most commonly isolated from wood in service and are 

frequently used in evaluation of wood preservative 

formulations.

Preservative Treatment Application

EPA-Registered Preservatives

Blocks for soil-block tests (19 mm3

) were cut from the 

sapwood of Southern Pine and yellow-poplar lumber, 

weighed, sorted by density, and then immersed for either 

1 or 3 min into the diluted preservative solutions (Table 3). 

Groups of 18 blocks were dipped for each species. Fifteen 

of the blocks were used for fungal testing, and the other 

three were reserved. The blocks were reweighed to 

determine uptake of preservative solution (Table 3) and then 

allowed to air-dry for 1 week prior to leaching.

Green Preservatives

Soil-block specimens (19 mm3

) for green preservatives were 

treated in the same manner as described for EPA-registered 

preservatives, with a few exceptions. Some of the products 

evaluated claimed that only one application was needed, 

whereas others indicated that two applications would

improve performance. Given that two applications might 

increase application cost and complexity for WPMs and in 

the interest of direct comparison, we evaluated all products 

with a single, 1-min dip, which is current commercial 

Figure 2. Soil-block test configuration. practice. This allowed comparison with earlier tests of EPA-
Evaluation of Nonpressure Wood Preservatives for Military Applications

7

registered wood preservative formulations. However, two of 

the products (Cedar and LiqSil) were also evaluated in a 

manner more closely matching manufacturer’s instructions 

(Table 4). All specimens were then air-dried for 1 week 

prior to leaching.

Leaching

Leaching was conducted on all specimens using simulated 

rainfall, rather than immersion, to better correspond to 

anticipated in-service exposure conditions (Fig. 3). 

Specimens were placed on wire racks in a rainfall simulator 

in which they were sprayed with rainfall at a rate of 

10 mm/h. An alternating schedule of 1 h rainfall and 5 h rest 

was used until a total of 20 h, or 200 mm, of rainfall 

occurred (5 days). After leaching, the blocks were 

reconditioned to a constant weight in an environmental 

chamber maintained at 27 °C and 30% relative humidity 

(RH).

Decay Testing

Blocks were placed, singly, into the previously inoculated 

soil bottles and maintained in an incubation chamber (27 °C 

and 80% RH) for 8 weeks and 12 weeks for EPA-registered 

preservatives and green preservatives, respectively. After 

fungal exposure, the blocks were brushed to remove fungal 

mycelium and reconditioned to constant weight in a room 

maintained at 27 °C and 30% RH. The blocks were then 

reweighed to determine percentage weight loss.

Table 3—Uptake of preservative in soil blocks after dip treatment 

(EPA-registered formulations)

Preservative Concentration

Dip time

(minutes)

Southern Pine weight gain (g) Yellow-poplar weight gain (g)

Average Std. dev. Average Std. dev.

Water none 1 1.71 0.27 0.74 0.14

CuC 1% as Cu 1 0.86 0.16 0.87 0.16

2% as Cu 1 0.89 0.19 0.89 0.12

AzI 1.05% total 1 1.46 0.23 0.96 0.20

1.05% total 3 1.50 0.42 1.11 0.25

pCuA-1 1% as Cu 1 0.89 0.17 0.77 0.19

2% as Cu 1 0.95 0.16 0.92 0.24

sCuA 1% as Cu 1 1.13 0.23 0.86 0.16

2% as Cu 1 1.27 0.39 0.84 0.30

pCuA-2 1% as Cu 1 1.22 0.19 0.72 0.18

2% as Cu 1 1.25 0.13 0.60 0.15

Cu8-1 1.2% as Cu-8 1 1.08 0.30 1.07 0.22

1.2% as Cu-8 3 1.60 0.32 1.11 0.18

1.8% as Cu-8 1 0.94 0.23 0.94 0.14

Cu8-2 1.2% as Cu-8 1 0.98 0.11 1.06 0.24

1.8% as Cu-8 1 0.91 0.13 0.96 0.12

CuN 1% as Cu 1 1.08 0.18 1.21 0.42

2% as Cu 1 1.18 0.22 1.09 0.15

ZnN 2.9% as Zn 1 1.10 0.20 0.90 0.13

Table 4—Summary of formulations and application methods for green preservatives

Formulation (short name) Concentration Application method

Cedar–organosilicon (Cedar) As is 1-min dip

Cedar–organosilicon (Cedar) As is 30-s dip, 3-min dry, 30-s dip

Silica gel wood stabilizer (LiqSil) As is 1-min dip

Silica gel wood stabilizer (LiqSil) As is Brush coat, 24-h dry, brush coat

Natural minerals (Mineral-1) As is 1-min dip

Natural materials (Mineral-2) As is 1-min dip

Polymer seal (Polymer) As is 1-min dip

Deck water-repellent (Deck WR) As is 1-min dip

Azoles/imidacloprid (AzI) 0.5% actives 1-min dip

Zinc naphthenate (ZnN) 3% zinc 1-min dip

Water As is 1-min dip
Research Paper FPL–RP–693

8

Laboratory Termite Tests

Wood Test Specimens

Southern Pine and yellow-poplar wood samples were cut 

into 25- (radial) by 25- (tangential) by 6- (longitudinal) mm 

blocks. Specimens with 5 to 8 growth rings were then 

selected for treatment.

Preservative Treatment Application

EPA-Registered Preservatives

Wood samples were placed in staining trays, separated by 

plastic mesh for dip treatments (Fig. 4). Trays were then 

submerged into glass staining dishes containing the 

preservative for either 1 or 3 min on a shaker depending on 

the treatment. Blocks were then removed from the trays, 

blotted gently to remove excess liquid, and weighed to 

determine uptake of the preservative. Samples were left to 

dry in a hood for 1 week and then conditioned to a uniform 

moisture content in a 27 °C, 30% RH incubator prior to 

leaching.

Green Preservatives

Test specimens were weighed and then immersed for 1 min 

into the test solution or treated as described in Table 4. 

Following drying and leaching, blocks were conditioned to 

constant weight in a room maintained at 27 °C and 30% RH

prior to leaching.

Leaching

As in decay tests, all specimens for termite testing were 

leached on wire racks in a rainfall simulator in which they 

were sprayed with rainfall at a rate of 10 mm/h. An 

alternating schedule of 1 h rainfall and 5 h rest was used 

until a total of 20 h, or 200 mm, of rainfall occurred 

(5 days).

No-Choice Termite Tests

The methods used in this study were patterned according to 

ASTM D 3345-08 (ASTM 2008). The no-choice testing 

arenas consisted of small, plastic dishes containing 50 g 

sterile, filtered sand and 9 mL deionized water, with test 

specimens placed on top of the sand. One gram of eastern 

subterranean termites, Reticulitermes flavipes (Kollar), 

collected from Janesville, Wisconsin, was then added to 

each container. Testing arenas were maintained in an 

incubator at 27 °C and 80% RH for the 4-week testing 

period. After the test, blocks were removed, brushed free of 

debris, dried in a hood, and reconditioned to a uniform 

moisture content before final weights were obtained. 

Termites from each container were separated into dishes for

mortality to be determined.

Statistical Analysis of Decay and Termite 

Tests

EPA-Registered Preservatives

To compare the preservative treatment groups for each 

organism–wood species combination, percentage weight 

losses from the soil-block decay tests and the termite tests 

were each analyzed using heteroscedastic linear models in 

SAS V9.4 (SAS Institute, Inc., Cary, NC). Families of 

comparisons were constructed to compare percentage

weight losses between treatments and the positive control 

(ZnN), as well as to test for possible changes caused by

treatment concentration or dip treatment time. Other 

comparisons, such as comparing treatment groups to the 

negative control (water) were also included but not reported.

Simulation-based multiple comparison adjustments were 

used as described in Westfall and others (2011).

Green Preservatives

The weight losses from the laboratory decay and termite 

tests were compared with the water-treated negative control 

and the results obtained with ZnN and 0.5% AzI (positive 

controls). One-way analyses of variances with treatment as 

the factor (at 11 levels) were carried out on percentage

Figure 3. Device used to subject specimens to leaching 

with simulated rainfall.

Figure 4. Termite specimen preparation for dip treatment.
Evaluation of Nonpressure Wood Preservatives for Military Applications

9

weight loss in SAS V9.4. These analyses were conducted 

separately for each wood species–test organism 

combination. Multiple pairwise comparisons were adjusted 

based on the Tukey–Kramer method in SAS, with adjusted 

p-values <0.05 considered significant.

Above-Ground Field Exposure (In Progress)

Laboratory fungal decay and termite tests have the 

advantage of producing relatively rapid results under 

controlled conditions. However, they do not include factors

such as weathering, wetting–drying cycles, and possible 

effects of secondary organisms such as bacteria. To create 

more realistic exposure conditions, specimens treated with 

EPA-registered preservatives and one green preservative 

(Cedar) are also being tested in outdoor exposure.

Testing methods followed AWPA Standard E18 (AWPA 

2017). In this method, groups of concrete blocks are placed 

flat on the ground with the distance from the top of the 

block to the ground at approximately 100 mm. Specimens 

are placed on top of the cinder blocks, and then the 

assembly is covered with a shade cloth frame. The shade 

cloth allows wetting but slows drying of the specimens, 

creating an environment more conducive to both decay and 

termite attack. Specimens will be inspected annually and 

given a numerical rating for extent of decay and termite 

attack. This test will be conducted for 5 years, at which time 

the specimens will be returned to FPL, conditioned to 

constant moisture content, and weighed to allow calculation 

of percentage weight loss.

Test blocks were treated in groups of five replicates (one set 

for each wood species) in stainless steel pans, with blocks 

weighted down with stainless steel weights and covered 

with 2,000 g of treatment solution. Dip times were 1 or 

3 min, with the exception of the Cedar specimens. Those 

specimens were dipped for 30 s, followed by a 3-min rest 

period, and then dipped for an additional 30 s. After

dipping, the specimens were allowed to drip for 5 min and 

then weighed to determine solution uptake (Table 5). They 

were then dried under ambient laboratory conditions for 

14 days before being placed in a room maintained at 70 °C 

and 50% RH to equilibrate. Additional sets of 13 untreated 

specimens of each species were also prepared. These

specimens were placed on top of three sets of six concrete 

blocks; the specimens were assigned to the blocks in such a 

way that each treatment group was represented in each set 

of six blocks. The specimens will be evaluated annually and 

given ratings for the extent of fungal decay and termite 

attack, which will be published in a subsequent report.

Corrosion Tests (EPA-Registered 

Preservatives Only)

In the manufacturing process, galvanized wires are attached 

to several sheets of plywood and the assembly is dipped in 

the preservative treatment for 1 min before being removed 

from the bath. The plywood assemblies are then stored flat 

in stacks until they are ready to be shipped. Because of how 

the boxes are stacked, air flow is restricted to boxes in the 

middle of the stack. It has been observed that boxes dipped 

in Cu8 and CuN will occasionally arrive with red rust when 

delivered to the army from the manufacturer, indicating that 

the galvanized coating has been corroded entirely.

The goal of the laboratory testing was to determine which 

preservative systems are the least likely to cause corrosion 

issues in the packaging crates. The test methodology was 

designed to simulate the production process of the wirebound crates (Zelinka and Lebow 2015). To simulate the 

production process, wires were attached to thin strips of 

plywood, which were then dipped in the preservative 

treatment for 1 or 3 min and then stored in polyethylene 

bags for either 2 or 8 weeks. The sealed polyethylene bags 

were used to simulate the slow drying with little air flow 

encountered for the stacked boxes. This represents, in some 

ways, a worst case scenario because there was no air flow 

and little potential for the wood to dry. Preliminary testing 

compared exposures in a room with 90% RH to the 

polyethylene bag exposure. In the preliminary testing, less 

corrosion was observed in the 90% RH room. However, it 

was hard to differentiate the performance of the wires 

exposed to different preservative systems. The polyethylene 

bag method was chosen because little corrosion was 

observed on the wires exposed to treatments that were 

known to be noncorrosive yet still able to produce 

measureable corrosion in other preservative systems, which

allowed differentiation of the preservative systems.

Both the wires and the wood strips used in the testing came 

from untreated packaging crates that were disassembled. 

The wires were removed from the crates and cut into 

segments that were approximately 150 mm long (the actual 

size of each segment was measured and recorded). 

Additional segments of wire were examined using scanning 

electron microscopy to examine the galvanization (a 

characteristic micrograph is shown in Fig. 5). In most 

places, the thickness of the galvanized coating was between 

10 and 20 μm.

Prior to the exposure test, the wires were cleaned in an 

ultrasonic bath with a soap solution, rinsed with distilled 

water, and finally rinsed with acetone. After the cleaning 

procedure, the wires were weighed and then attached with a 

plastic fastening ring to a small (25- by 178-mm) strip of 

wood cut from the packaging crate. These assemblies of 

wood and wire were then dipped into the preservative 

treatment solutions, removed, and stored in a polyethylene 

bag for either 2 or 8 weeks.

Following the exposure, the extent of the corrosion was 

examined both qualitatively with a visual examination and 

quantitatively by gravimetric analysis. Photographs of the
Research Paper FPL–RP–693

10

wires were taken immediately after removal from the 

polyethylene bags. Afterward, the plastic fastening rings 

were removed and the wires were flipped over and 

photographed again. This second photograph showed both 

the extent of corrosion when the wire was in direct contact 

with the wood and also the amount of corrosion products 

deposited on the wood surface. Gravimetric analysis was 

performed by first removing the corrosion products of metal 

in contact with wood using the method of Zelinka and 

Rammer (2009). The wires were placed in an ultrasonic 

cleaner for 60 min in a bath comprised of 1:1 

water/EvapoRust solution (Orison Marketing, Abilene, 

Texas). The wires were then wiped dry and weighed.

The preservatives evaluated, their compositions and 

concentrations, and the time the wood and wires were 

dipped in the treatment solution are shown in Table 6. All 

but two treating solutions (AzI, ZnN) contained 2% or less 

of copper and various types and amounts of organic 

biocides. Previous research has shown that the amount of 

copper in preservative treatments strongly affects the 

corrosiveness of the treated wood and that the effect of the 

organic biocides is small compared with other differences in 

preservatives such as pH and copper concentration (Kear 

and others 2009, Zelinka 2014, Zelinka and Stone 2011). 

Two preservatives did not contain copper: ZnN, which had 

less than 3% concentration of zinc, and AzI, which 

Figure 5. Scanning electron micrograph of the wires 

tested. Two different wire segments are shown.

Table 6—Preservatives and concentrations

evaluated in corrosion testing

Preservative Concentrations evaluated

Dip times 

(min)

CuC 2% as Cu 1

AzI 1.05% total actives 3

Cu8-1 1.8% as Cu-8-quinolinolate 3

Cu8-2 1.8% as Cu-8-quinolinolate 1

CuN 2% as Cu 1

pCuA-2 2% as Cu 1

Water — 1

ZnN 2.9% as Zn 1

Table 5—Uptake of preservative in field exposure specimens after dip treatment

Preservative Concentration

Dip time

(min)

Southern Pine weight gain (g) Yellow-poplar weight gain (g)

Average Std. dev. Average Std. dev.

CuC 1% as Cu 1 4.07 0.30 3.34 0.56

2% as Cu 1 4.65 0.40 3.40 0.35

AzI 1.05% total 1 6.10 0.49 3.56 0.74

1.05% total 3 8.64 2.49 4.34 0.78

pCuA-1 1% as Cu 1 4.20 0.15 2.95 0.55

2% as Cu 1 4.62 0.76 3.05 0.46

sCuA 1% as Cu 1 5.50 0.78 4.15 0.72

2% as Cu 1 5.18 0.47 4.17 1.18

pCuA-2 1% as Cu 1 5.32 0.87 3.01 0.81

2% as Cu 1 4.72 0.67 2.43 0.54

Cu8-1 1.2% as Cu-8 1 5.69 1.24 3.90 0.76

1.2% as Cu-8 3 6.09 0.95 3.35 0.37

1.8% as Cu-8 1 5.11 0.88 3.21 0.30

Cu8-2 1.2% as Cu-8 1 4.65 0.61 3.86 0.61

1.8% as Cu-8 1 5.18 0.83 3.20 0.82

CuN 1% as Cu 1 5.01 1.02 4.80 1.08

2% as Cu 1 4.55 0.67 4.52 1.47

ZnN 2.9% as Zn 1 6.26 0.92 3.34 0.36

Cedar As is 0.5, 0.5a 5.23 0.49 1.87 0.14

a

Based on manufacturer recommendations, these specimens were dipped for 30 s, allowed to rest for 3 min, and then dipped for another 30 s.
Evaluation of Nonpressure Wood Preservatives for Military Applications

11

contained only organic biocides. In addition to these nine

preservative treatments, a water control group (U) was 

tested. In this group, the wood–wire assemblies were dipped 

in a bath of deionized water for 1 min and sealed in 

polyethylene bags.

Results and Discussion, EPARegistered Preservatives

Fungal Soil-Block Tests

Southern Pine

The most effective preservatives were Cu8-2 and AzI,

which allowed little if any decay (Fig. 6). The higher 

solution concentration (1.8%) of Cu8-1 also provided 

excellent protection of Southern Pine. However, substantial 

weight loss did occur with some of the other preservative–

concentration–fungus combinations. CuC appeared to be the 

least effective at protecting Southern Pine, although the 

lower concentrations of pCuA-1, sCuA, and CuN were also 

heavily attacked by the fungus P. placenta. The soft-rot 

fungus C. globosum caused little weight loss, even in the 

controls, and thus provided limited information on 

preservative efficacy. A statistical analysis was conducted to 

compare the performance of test preservatives to those 

currently allowed under military specifications (ZnN, 

Cu8-1, Cu8-2, and CuN). Table 7 summarizes the results of 

that statistical analysis. Each column shows which 

preservative–concentration combinations suffered 

significantly more weight loss (performed more poorly) than 

each of the reference preservatives. CuC (both 

concentrations) and CuN (1% concentration) often allowed 

significantly more weight loss than the reference 

preservatives for one or more of the fungi evaluated. The 

1% concentrations of pCuA-1 and sCuA also allowed 

significantly more weight loss than the reference 

preservatives when challenged with the fungus P. placenta.

AzI and pCuA-2 did not allow significantly more weight 

loss than any of the reference preservatives–fungi evaluated.

In the case of pCuA-2, one or more blocks exposed to 

P. placenta did have substantial weight loss at each solution 

concentration, whereas the other blocks were not degraded

(Table 8). This variability between replicates may have 

prevented a finding of statistically significant difference 

between the performance of pCuA-2 and that of any of the 

reference preservatives. Similar variability was observed

within blocks treated with 2% pCuA-1 and 2% CuN. This 

high degree of variability within replicates is unusual but 

may be a function of the dip-treatment process (typically 

soil blocks are vacuum–pressure impregnated).

Yellow-Poplar

Most of the test preservatives were highly effective in 

protecting yellow-poplar from fungal attack (Fig. 7). The 

exception was the lower (1%) concentration of CuC, which 

did allow substantial decay by the fungus I. lacteus.

Interestingly, the preservatives that were least effective in 

protecting yellow-poplar were Cu8-1 and ZnN, both of 

which are already allowed under military specifications.

Figure 6. Average weight losses in Southern Pine cubes treated with the preservatives shown. Error bars show plus or 

minus one standard deviation from the mean.
Research Paper FPL–RP–693

12

Statistical analysis indicated that Cu8-1 and ZnN were also 

the only preservatives to allow significantly greater weight 

loss than any of the reference preservatives (in this case, the 

reference preservatives were limited to 1.8% Cu8-2 and 2% 

CuN) (Table 9). However, 1% pCuA-2 had marginally 

greater weight loss than 2% CuN in yellow-poplar exposed 

to T. versicolor. Statistical analyses sometimes produce 

results that we might find counterintuitive. CuC exposed to 

I. lacteus had greater weight loss than 1% pCuA-2 exposed 

to T. versicolor, but the CuC result was not statistically

significant because of the greater variability associated with 

those comparisons. As with Southern Pine, soft-rot 

C. globosum resulted in such little weight loss in the 

controls that it provided little information on preservative 

efficacy.

Table 7—List of formulations that provided less fungal protection to Southern Pine than the reference 

preservatives at either the 90% or 95% confidence levels

Reference preservative

Decay fungus and confidence level

G. trabeum

90%

G. trabeum

95%

P. placenta

90%

P. placenta

95%

ZnN, 2.9% Zn None None CuC, 1%

CuC, 2%

CuN, 1%

sCuA, 1%

pCuA-1, 1%

CuC, 1%

CuC, 2%

CuN, 1%

sCuA, 1%

Cu8-2, 1.8% CuC, 1%

CuC, 2%

CuN, 1%

CuC, 1% CuC, 1%

CuC, 2%

CuN, 1%

sCuA, 1%

pCuA-1, 1%

CuC, 1%

CuC, 2%

CuN, 1%

sCuA, 1%

pCuA-1, 1%

Cu8-1, 1.8% CuC, 1%

CuC, 2%

CuN, 1%

CuC, 1% CuC 1%

CuC 2%

CuN 1%

sCuA, 1%

pCuA-1, 1%

CuC, 1%

CuC, 2%

CuN, 1%

sCuA, 1%

pCuA-1, 1%

CuN, 2% Cu CuC,1%

CuC, 2%

CuN, 1%

None CuC, 1%

CuC, 2%

CuN, 1%

pCuA-1, 1%

CuC 1%

CuC 2%

CuN 1%

Table 8—Individual soil-block percentage weight losses for Southern Pine blocks decayed by Postia placenta

Preservative Concentration Dip time (min)

Replicate number

1 2 3 4 5 Mean

Water none 1 59.16 61.13 59.01 57.03 63.29 59.92

CuC 1% as Cu 1 65.35 66.28 58.66 48.05 63.03 60.27

2% as Cu 1 63.07 63.26 39.20 62.92 53.84 56.46

AzI 1.05% total 1 -0.21 0.00 -0.23 0.67 0.72 0.19

1.05% total 3 -0.23 0.03 0.08 0.41 -0.08 0.04

pCuA-1 1% as Cu 1 42.69 54.61 22.84 21.78 48.62 38.11

2% as Cu 1 0.31 0.31 0.52 0.00 31.62 6.55

sCuA 1% as Cu 1 53.08 55.73 57.71 42.14 38.77 49.49

2% as Cu 1 1.05 1.57 0.46 10.86 0.76 2.94

pCuA-2 1% as Cu 1 0.59 22.13 0.51 1.39 1.11 5.15

2% as Cu 1 0.26 0.08 13.73 8.65 27.09 9.96

Cu8-1 1.2% as Cu-8 1 11.29 0.10 0.18 0.31 0.71 2.52

1.2% as Cu-8 3 0.54 0.03 0.13 0.10 0.10 0.18

1.8% as Cu-8 1 0.25 0.35 0.61 0.94 -0.10 0.35

Cu8-2 1.2% as Cu-8 1 0.43 0.40 0.33 0.89 0.53 0.52

1.8% as Cu-8 1 0.25 0.35 0.61 0.94 -0.10 0.41

CuN 1% as Cu 1 55.01 60.49 38.11 50.28 63.24 53.43

2% as Cu 1 0.34 14.11 17.50 0.87 0.18 6.60

ZnN 2.9% as Zn 1 1.02 0.49 0.46 8.89 11.95 4.56
Evaluation of Nonpressure Wood Preservatives for Military Applications

13

Effect of Solution Concentration

A statistical analysis was conducted to determine if solution 

concentration significantly affected weight loss. The 

analysis indicated that the performance of the 2% CuC was 

significantly better than that of the 1% solution when 

Southern Pine wood was exposed to G. trabeum or when 

yellow-poplar was exposed to I. lacteus. The higher 

concentrations of pCuA-1 and sCuA also provided 

significantly greater protection when Southern Pine was 

exposed to G. trabeum or P. placenta. In contrast, pCuA-2, 

Cu8-1, and Cu8-2 did not provide significantly greater 

protection at the higher solution concentration.

Effect of Dip Time

AzI (1.05%) and Cu8-1 (1.2%) were evaluated using both 1-

and 3-min dip times. The longer dip time did not result in a 

statistically significant increase in protection in either case.

Because AzI was highly effective with the 1-min dip in all 

cases, a significant improvement with the longer dip time 

could not be determined.

Additional Evaluation of Copper Tolerance

The extent of copper tolerance observed for P. placenta in 

this study was somewhat surprising given the efficacy of 

several of the preservatives when used for pressure 

treatment of wood placed in contact with the ground. 

Although the specimens used in this study were dip-treated 

rather than pressure-treated, the solution concentration used 

was relatively high. To further evaluate the effect of 

treatment process (dip versus pressure), additional sets of 

Southern Pine blocks were either dipped for 3 min or 

vacuum-impregnated with 1% concentrations of copperbased preservatives. The vacuum treatment involved 30 min 

Figure 7. Average weight losses in yellow-poplar cubes treated with the preservatives shown. Error bars show plus or 

minus one standard deviation from the mean.

Table 9—List of formulations that provided less fungal protection to yellow-poplar than the reference 

preservatives at either the 90% or 95% confidence level

Reference preservative

Decay fungus and confidence level

T. versicolor

90%

T. versicolor

95%

I. lacteus

90%

I. lacteus

95%

ZnN, 2.9% Zn None None None None

Cu8-2, 1.8% Cu8-1, 1.2%

Cu8-1, 1.8%

ZnN 3%

None Cu8-1, 1.2%

Cu8-1, 1.8%

ZnN, 3%

Cu8-1, 1.2%

Cu8-1, 1.8%

ZnN, 3%

Cu8-1, 1.8% None None None None

CuN, 2% Cu pCuA-2 None Cu8-1, 1.2%

Cu8-1, 1.8%

ZnN, 3%

Cu8-1, 1.2%

Cu8-1, 1.8%

ZnN, 3%
Research Paper FPL–RP–693

14

immersion at –94 kPa (gauge) followed by 30 min 

immersion at atmospheric pressure. Based on weight gain 

following treatment, the dip- and vacuum-treated specimens 

absorbed an average of 1.2 and 4.5 g of treatment solution,

respectively. The treated specimens were air-dried and

subsequently leached prior to being exposed to P. placenta

in soil-block testing as described earlier.

As shown in Figure 8, vacuum impregnation yielded a 

dramatic decrease in weight loss caused by the fungus 

P. placenta. The interesting exception was CuN, in which 

the dip treatment also provided good protection. This 

finding is notable because the 1% CuN dip-treated blocks 

were highly susceptible to attack by P. placenta when 

dipped for only 1 min (Table 8). It is possible that the 

additional 2 min of dip time provided sufficient naphthenic 

acid to deter the test fungus. An increase in efficacy was not 

observed with longer dip time for Cu8-1 in earlier testing, 

and it is possible that the effect of dip time on efficacy is 

formulation-dependent. In general, this supplemental testing 

indicates that dip-treated (that is, surface-treated) specimens 

may be more vulnerable to degradation by copper-tolerant 

fungi than pressure-treated specimens. Recent research also 

suggests that copper tolerance is a function of fungus 

adaptability to a copper-rich environment (Jenkins and 

others 2014). In theory, the copper ions are more readily 

chelated by natural byproducts of P. placenta, such as 

oxalate, in surface-treated specimens. It is also possible that 

surface-treated copper ions could be easier for the fungus to 

bypass compared with pressure-treated copper. Research 

also showed that test specimens surface-treated with 1.2% 

copper citrate and exposed to copper-sensitive G. trabeum

only marginally inhibited decay, whereas specimens 

pressure-treated with 1.2% copper citrate completely 

inhibited decay (Jenkins and others 2014).

Laboratory Termite Tests

Mean percentage weight loss for each test group and termite 

mortality classification results are shown in Table 10. 

Termite mortality is estimated as follows, slight (0–33%), 

moderate (34–66%), heavy (67–99%), or complete (100%).

Despite leaching, the majority of preservative dip treatments 

showed resistance to termite feeding either through 

repellency and/or direct toxicity of the preservative to the 

termites. The six most promising treatments in terms of 

weight loss to wood specimens were 1.05% AzI, 2% CuC,

2% sCuA, 2% pCuA-2, 1.8% Cu8-2, 1% or 2% CuN, and 

2.9% ZnN. Treatments that showed higher amounts of 

termite feeding were 1.2% and 1.8% Cu8-1, suggesting that 

they may not perform as well as other treatments in a field 

situation with termite exposure.

A statistical analysis was conducted to determine which 

experimental treatments, if any, allowed more weight loss 

than preservatives currently allowed under military 

specifications (Table 11). None of the experimental 

treatments allowed greater weight loss than ZnN in 

Southern Pine blocks, with the exception of the Cu8-1

formulation. In yellow-poplar, ZnN provided significantly 

greater protection than the lowest concentration of several 

preservatives evaluated (Table 11) as well as all 

formulations of Cu8-1. Cu8-2 (1.8%) had significantly less 

weight loss than ZnN and all Cu8-1 formulations in 

Southern Pine but did not offer significantly greater 

protection (95% confidence level) than any of the other 

formulations in yellow-poplar. 1.8% Cu8-1 suffered the 

greatest weight loss of any formulation in Southern Pine and 

nearly the greatest weight loss in yellow-poplar and did not 

provide significantly greater protection than any other 

preservative. A substantial number of significant differences 

were observed when other formulations were compared with

the reference preservative 2% CuN. This is because 2% 

CuN suffered virtually no weight loss and had little 

variation between replicates. The only formulations that did 

not allow significantly more weight loss than 2% CuN were 

AzI and 2% sCuA.

Dip times of 1 min compared with 3 min did not seem to 

make a difference in overall results. In terms of weight loss, 

however, there was a difference between wood species. In 

the controls, weight loss of Southern Pine blocks was 

slightly higher than yellow-poplar blocks. However, in a 

number of the treated groups, yellow-poplar showed higher 

amounts of feeding than Southern Pine. Interestingly, 

termite mortality tended to be more moderate in yellowpoplar, despite the higher levels of feeding. Future studies 

should determine if it is possible that certain preservative 

treatments were more readily leached from yellow-poplar 

Figure 8. Average percentage weight loss for 1% (as Cu) than from Southern Pine.

formulations applied by either dip or vacuum treatment 

and exposed to Postia placenta. Error bars represent one 

standard deviation from the mean.
Evaluation of Nonpressure Wood Preservatives for Military Applications

15

Table 10—Percentage weight loss of test specimens and termite mortality classification (dip 

treatment times are 1 min unless otherwise noted)

Preservative

formulation

Percentage 

weight loss, 

Southern

Pine

Termite mortality 

classification

Percentage 

weight loss, 

yellow-poplar

Termite mortality 

classification

1% CuC 1.61 Heavy 8.23 Moderate

2% CuC 0.00 Heavy 2.43 Heavy

1.05% AzI 0.00 Complete 0.00 Complete

1.05% AzI (3-min dip) 0.00 Complete 0.00 Complete

1% pCuA-1 1.96 Heavy 11.52 Moderate

2% pCuA-1 0.00 Heavy 6.61 Moderate

1% sCuA 0.24 Heavy 6.64 Moderate

2% sCuA 0.00 Heavy 1.77 Heavy

1% pCuA-2 0.44 Heavy 10.1 Moderate

2% pCuA-2 0.43 Heavy 3.84 Moderate

1.8% Cu8-1 4.32 Moderate 12.35 Moderate

1.2% Cu8-1 8.63 Moderate 11.83 Moderate

1.2% Cu8-1 (3-min dip) 14.87 Moderate 11.33 Moderate

1.2% Cu8-2 0.28 Heavy 9.13 Moderate

1.8% Cu8-2 0.57 Heavy 5.74 Moderate

1% CuN 0.55 Heavy 0.74 Heavy

2% CuN 0.00 Heavy 0.00 Heavy

2.9% ZnN 1.59 Heavy 2.34 Heavy

Untreated wood 19.59 Slight 17.33 Moderate

Table 11—Preservatives with significantly (95% confidence) greater termite weight loss than 

reference preservatives currently specified

Reference preservative Southern Pine Yellow-poplar

ZnN, 2.9% Zn Cu8-1, 1.2%

Cu8-1, 1.2%, 3-min dip

Cu8-1, 1.8%

CuC, 1%

pCuA-2, 1%

Cu8-2, 1.2%

Cu8-1, 1.2%

Cu8-1, 1.2%, 3-min dip

Cu8-1, 1.8%

sCuA, 1%

pCuA-1, 1%

Cu8-2, 1.8% Cu8-1, 1.2%

Cu8-1, 1.2%, 3-min dip

Cu8-1, 1.8%

ZnN, 3%

None (Cu8-1 had greater weight loss at the 90% 

confidence level)

Cu8-1, 1.8% None None

CuN, 2% Cu Cu8-1, 1.2%

Cu8-1, 1.2%, 3-min dip

Cu8-1, 1.8%

ZnN, 3%

CuC, 1%

CuC, 2%

pCuA-2, 1%

pCuA-2, 2%

Cu8-2, 1.2%

Cu8-1, 1.2%

Cu8-1, 1.2%, 3-min dip

Cu8-1, 1.8%

sCuA, 1%

pCuA-1, 1%

pCuA-1, 2%

ZnN, 3%
Research Paper FPL–RP–693

16

In terms of termite mortality with treatment, the most toxic 

treatment was AzI at 1.05% for both Southern Pine and 

yellow-poplar blocks. Within days of exposure to the treated 

blocks, mobility of the termites became arrested; even 

typical foraging behaviors were not observed. These groups 

began showing mortality between 1 and 2 weeks after the 

start of the test and had 100% mortality by the end of the 

4 weeks. The active component in the AzI treatment is 

likely to be imidacloprid because the insecticidal properties 

of this compound are already well characterized for termites

(Thorne and Breisch 2001). Imidacloprid is a neonicotinoid 

compound that affects the insect nervous system by 

targeting nicotinic acetylcholine receptors (Meijer and 

others 2014).

Combining Laboratory Fungal and Termite 

Results

Interpretation of the laboratory fungal and termite tests is 

somewhat complex because the results vary between fungal 

and termite exposure, as well as with wood species and type 

of fungus. Only one formulation, AzI, exhibited consistently 

high efficacy against all organisms and for both wood 

species. To simplify comparison between formulations, 

Figure 9 shows the combined total average weight loss 

allowed by each formulation across both wood species and

all organisms. About half the formulations evaluated yielded 

less than 20% total average weight loss. Included within this 

group were AzI, both concentrations of Cu8-2 (1.2% and 

1.8%), as well as the 2% concentrations of sCuA, pCuA-1,

pCuA-2, and CuN. The 1% pCuA-2 concentration was also 

within this group, although it allowed greater weight loss 

than its counterparts. Then there was a group of

formulations that allowed at least 50% total average weight 

loss, including two of the reference preservatives, ZnN and 

1.8% Cu8-1. The higher (2%) concentration of CuC was

also within this group because it was found to be effective 

against most organisms but was severely degraded by the 

fungus Postia placenta in Southern Pine. The greatest total 

weight loss occurred with 1% CuC, which was severely 

degraded by three types of fungi and somewhat degraded by 

termites in yellow-poplar.

It is apparent from Figures 6 and 8 that the fungus 

P. placenta was a major cause of weight loss in Southern 

Pine specimens treated with several of the copper-based 

formulations. P. placenta is known to have some degree of 

copper tolerance and can sometimes damage wood in which 

copper is the only biocide. There are other wood decay 

fungi that also have this ability, and thus copper-based 

preservatives typically also contain cobiocides (that is,

naphthenic acid in CuN, quinolinolate in Cu8, and azoles in 

copper azole formulations) to help prevent attack by coppertolerant fungi. These cobiocides appeared to be fairly 

effective at higher concentrations, although some 

degradation still occurred in several preservatives. As 

previously noted, the CuC formulation was particularly 

vulnerable to this fungus, even at the higher 2% 

concentration.

The practical consequences of a preservative being 

vulnerable to copper-tolerant fungi warrants further 

discussion. There is some evidence that the risk of 

degradation by copper-tolerant fungi is primarily a concern 

for wood placed in direct contact with soil. This is because 

wood placed in contact with the ground is exposed to the 

Figure 9. Average percentage weight loss for each formulation combined across all organisms (fungi and termites) and 

both wood species.
Evaluation of Nonpressure Wood Preservatives for Military Applications

17

fully developed fungal strands (mycelium) that exist in the 

soil. This mycelium is able to produce chemicals that help to 

detoxify the copper. Conversely, wood used above ground is 

primarily infected by air-borne fungal spores. These fungal 

spores appear to be less resistant to copper than the fully 

developed mycelial strands present in soil (Choi and others

2002). In many situations, the wooden material used in 

army shipping and storage containers is not placed in direct 

contact with the ground, and thus, decay is initiated by 

fungal spores. Copper tolerance may be less of a concern in 

these situations.

Corrosion Testing Results

Figure 10 shows the percentage weight loss after 2 weeks 

for each of the nine preservatives. The wires dipped in ZnN

had the lowest amount of corrosion and thus the lowest 

percentage weight loss. Surprisingly, wires exposed to 

seven of the preservatives exhibited a lower mean 

percentage weight loss than the water group. The most 

corrosion was exhibited in wires that had been treated with

pCuA-1. To determine differences among the groups, the 

means were compared using a Tukey honest significant 

difference test. There were no significant differences 

between ZnN and CuC. The mean percentage weight losses

from CuN, pCuA-2, and sCuA could not be differentiated 

but were higher than the group with ZnN and CuC. pCuA-1

had the most corrosion and was statistically different from 

the next lowest group.

Figure 11 shows the percentage weight loss after 8 weeks 

for each of the nine preservatives. Apparently, this exposure 

time was more realistic because the relative rankings of 

preservatives for which corrosiveness has been measured in 

previous experiments were consistent with previous testing

(Zelinka and Stone 2011). In samples exposed for 8 weeks, 

treatments CuC and ZnN clearly exhibited the least amount 

of corrosion and were at least five times less corrosive than 

the remaining treatments. Of the remaining preservatives, 

AzI was significantly lower than Cu8-2, Cu8-1, and CuN, 

but the difference between AzI and the water control was

not statistically significant. The soluble copper system had 

the most corrosion, and the difference between the soluble 

copper system and the next most corrosive system, pCuA-2,

was statistically significant.

Figure 12 shows the ratio of the percentage weight loss after 

8 weeks to the percentage weight loss after 2 weeks. If the 

corrosion rate was constant during this time period, the

expected ratio would be four. A ratio less than four indicates 

the corrosion rate was decreasing after 2 weeks. A ratio of 1 

suggests that all corrosion happened in the first 2 weeks.

Three preservative systems (pCuA-2, sCuA, and CuN) 

exhibited a ratio of 4, suggesting that the corrosion rate was 

constant throughout the test. These preservatives would be 

expected to have even more corrosion in longer exposure 

times because the rate was not decelerating. Two 

preservative systems, ZnN and CuC, had a ratio of 1, 

suggesting that the corrosion had stopped after 2 weeks and 

little if any further corrosion would be expected.

Figure 13 shows photographs of one wire from each group 

after the 2-week exposure. The wire that was dipped in ZnN

is in the bottom right corner and shows no signs of 

corrosion. The other wires had white corrosion products

consistent with the corrosion of zinc, although the degree of 

corrosion varied among the wires. The wires from AzI, 

which had no copper in the treatment solution, exhibited 

some minor splotches of red rust, indicating that the 

Figure 10. Percentage weight loss of wires after the 2-

week exposure. Error bars represent the standard error. 

The letters above the bars are results of the Tukey’s 

honest significant difference test; groups with the same 

letter have means that are not statistically different.

Figure 11. Percentage weight loss of wires after the 8-

week exposure. Error bars represent the standard error. 

The letters above the bars are results of the Tukey’s 

honest significant difference test; groups with the same 

letter have means that are not statistically different.
Research Paper FPL–RP–693

18

galvanized coating layer had corroded and the underlying 

steel wire was corroding. In addition to AzI, significant 

amounts of corrosion products were also visible on wires 

from pCuA-1, sCuA, Cu8-2, and the water-treated group.

Figure 14 shows the same wires as Figure 13 after they were 

rotated 180 degrees, exposing the metal that had been in 

direct contact with the wood. In some cases, the corrosion 

products became attached to the wood, and examining the 

wood that was in contact with the metal gave additional 

insights into the severity of corrosion. The back sides of the 

wire revealed that wires exposed to sCuA and Cu8-2 also 

had red rust that was not visible from the top view. Half of 

the treatments (CuC, pCuA-1, sCuA, Cu8-2, and CuN) 

resulted in white or red corrosion deposited on the wood.

Table 12 summarizes the visual inspection of the corrosion 

products by placing the different treatments into groups 

according to the amount of corrosion exhibited.

Figure 15 shows the top view of the wires after 8 weeks of 

exposure. All but two wires (CuC and ZnN) exhibited red 

rust. For the remaining groups, the red rust appeared as 

small, red dots on top of a layer of white corrosion products,

and these red dots were evenly distributed throughout the 

wire. Because of this distribution of rust, it was difficult to 

visually rank the different treatments exhibiting red rust 

based on the amount of wire covered with red rust.

Figure 16 shows the same wires as Figure 15 after they were

rotated 180 degrees to expose the metal that had been in 

direct contact with the wood surface. For six of the eight 

wires exhibiting red rust, corrosion products were deposited 

on the wood and differences between treatments could be 

observed. The amount of corrosion products deposited in the 

wood can be used to separate the treatments. These 

observations are summarized in Table 13, which groups the

Figure 14. Bottoms of wires after the 2-week exposure. 

Dip formulations from left to right. Top row: CuC, AzI, 

pCuA-1, sCuA, Cu8-1. Bottom row: Cu8-2, CuN, pCuA-2, 

water, ZnN.

Figure 12. Ratio of percentage weight loss after 8 weeks 

to percentage weight loss after 2 weeks (a ratio of 4 

indicates no deceleration in corrosion).

Figure 13. Tops of wires after the 2-week exposure. Dip 

formulations from left to right. Top row: CuC, AzI, pCuA1, sCuA, Cu8-1. Bottom row: Cu8-2, CuN, pCuA-2, water, 

ZnN.
Evaluation of Nonpressure Wood Preservatives for Military Applications

19

different treatments according to their corrosiveness.

different treatments according to their corrosiveness.

Corrosion Testing Discussion

The exposure condition was chosen to be a challenging 

representation of what may occur in the production of the 

wire-bound packaging crates. In the production process, the 

crates are typically stacked on top of each other, dipped, and 

then stored until they are shipped. This process is difficult to 

replicate in the laboratory because there are, in actuality, a 

wide range of potential conditions the boxes could face 

post-treatment, depending on the ambient environment and 

how tightly they are stacked. The polyethylene bag method 

was chosen because it represents a worst case scenario (that 

is, no air flow), and the goal of the test was to differentiate 

the formulations evaluated. However, this environment may 

have been overly challenging, because even the untreated 

controls (dipped in a water bath) exhibited red rust and 

significant corrosion in the 8-week test. Despite this, 

preservative treatments could be grouped into several 

categories according to their corrosiveness.

In all exposure conditions, the wires exposed to the ZnN

treatment exhibited little, if any, corrosion. Furthermore, 

they had five times less corrosion than wires that were 

strapped to wood and dipped in water, suggesting that ZnN

was acting as a strong corrosion inhibitor. This behavior 

should not be surprising, because the treatment is made up 

of soluble zinc ions and the wires are coated with solid zinc.

Unlike the preservatives with cupric ions, where it is 

thermodynamically favorable for the cupric ions to be 

reduced and the zinc to oxidize, the zinc ions in solution 

should not cause a displacement reaction. If anything, 

excess zinc ions in solution may solidify on the wire 

surface, increasing the thickness of zinc coating. This 

compatibility between the zinc ions in solution and the 

galvanized wires is the reason for the low amount of 

corrosion exhibited by the wires dipped in the ZnN solution.

CuC also exhibited an extremely low amount of corrosion 

relative to the other groups. Surprisingly, CuC contained 

cupric ions yet performed better than the untreated control 

group in which the wires were dipped in water. Because one 

of the likely corrosion mechanisms involves the reduction of 

cupric ions, one would expect this preservative to be more 

corrosive than the untreated group with just water. Beyond 

cupric ions, Zelinka and Stone (2011) have shown that 

preservative treatments can modify the pH of the wood, and 

as the pH is lowered, more corrosion is expected. CuC is 

Table 12—Summary of the corrosion visual inspection 

after the 2-week exposure

Condition Preservative

No visible corrosion ZnN

White rust, slight CuC, Cu8-1, CuN, pCuA-2

White rust, moderate to heavy AzI, pCuA-1, water

White and red rust on surface, heavy 

deposits on wood

Cu8-2, sCuA

Figure 15. Tops of wires after the 8-week exposure. Dip 

formulations from left to right. Top row: CuC, AzI, pCuA-1, 

sCuA, Cu8-1. Bottom row: Cu8-2, CuN, pCuA-2, water, 

ZnN.

Figure 16. Bottoms of wires after the 8-week exposure. 

Dip formulations from left to right. Top row: CuC, AzI, 

pCuA-1, sCuA, Cu8-1. Bottom row: Cu8-2, CuN, pCuA-2, 

water, ZnN.
Research Paper FPL–RP–693

20

alkaline (pH = 10.2), and this may be one reason why it was

less corrosive. However, two other preservatives, CuN and 

sCuA, have a pH above 9 and still exhibited more than five

times the corrosion as CuC. In short, from a chemical 

perspective, it is unclear why CuC had such a low corrosion 

rate. It is possible that this preservative contains a 

proprietary corrosion inhibitor or some other additive that 

resulted in the low observed corrosion rates.

The differences in corrosion among the remaining eight 

treatments were small, but they had a much higher corrosion 

rate than either ZnN or CuC. AzI had a significantly lower 

amount of corrosion than the other remaining preservatives

but was still much more corrosive than ZnN or CuC. The 

soluble copper azole solution (sCuA) had the greatest 

amount of corrosion, which was expected.

In addition to ranking the amount of corrosion after the 

8-week test, the ratio of the corrosion rate between the 2-

and 8-week tests can be used to identify preservatives for 

which corrosion rate was not decreasing with time. The ratio 

of the percentage weight loss between the 8- and 2-week 

tests was equal to the ratio of exposure time (4) for pCuA-2,

sCuA, and CuN. This ratio indicates that the corrosion rate 

did not change during the exposure time and suggests that 

the amount of corrosion could continue to increase at the 

same rate for longer exposures. Because the corrosion rate is 

not slowing down with time, these preservatives may have a 

higher likelihood of causing corrosion problems if the crates 

are exposed to prolonged wetting.

The results of these tests can be used to compare the relative 

amounts of corrosion that would be expected to occur in the 

production of the boxes. The amount of corrosion that the 

packaging materials exhibit not only depends on the 

preservative treatment but is a strong function of the wood 

moisture content (Zelinka and others 2014). Manufacturing 

processes that allow the packaging materials to dry more 

quickly after treatment may help prevent corrosion 

problems.

Summary of Corrosion Testing

Nine different preservative treatments and an untreated 

control were evaluated for their corrosiveness toward wirebound packaging crates. Wires were attached to strips of 

wood, dipped in the preservative treatment, and then stored 

in a polyethylene bag for either 2 or 8 weeks to simulate the 

time between treatment and shipment. After 8 weeks, seven 

of the nine preservatives and the untreated control caused 

red rust to form on the galvanized wires.

The only two wires that did not exhibit red rust were those 

treated with ZnN, which was previously the most commonly 

used preservative, and CuC. The active biocides in CuC

were similar to other preservatives tested, and it is unclear 

why this preservative exhibited such a low amount of 

corrosion.

The percentage weight loss of three of the preservatives 

(pCuA-2, sCuA, and CuN) increased linearly with time, 

indicating the corrosion rate was constant through the 

8-week test. These preservatives may have a higher

likelihood of corrosion problems because the corrosion rate 

was not decelerating with time.

The goal of this research was to find alternatives to ZnN that 

do not pose a corrosion concern. The testing clearly 

indicated that CuC was the least corrosive alternative. The 

remaining preservatives all exhibited red rust in the 8-week

test and more than five times the corrosion that was 

observed in the ZnN solution.

Verifying Treatment and Solution 

Concentration

Verifying preservative treatment is an important part of 

conformance inspections, and treaters need a method of 

verifying the concentration of the treatment solution. 

Existing military specifications describe methods for 

verifying the presence of ZnN, Cu8, or CuN preservative on 

wooden materials. These methods rely on the use of 

colorimetric indicator solutions that react to the presence of 

active ingredients in the preservative (Table 14). The 

indicator currently used for CuN could also be used for the 

other soluble and particulate copper formulations evaluated 

in this study. The dark color imparted by the CuN and CuC 

formulations is also an indicator of treatment (Fig. 17) and 

should make any untreated areas readily apparent. Verifying 

preservative treatment is most challenging for the AzI 

formulation, which is a clear formulation that does not 

impart an obvious color change to the treated wood. Also, 

AzI does not contain copper or zinc, which have available

colorimetric indicator solutions listed under military 

specification. In the pressure-treatment industry, detection 

of colorless treatments is addressed by adding a more easily 

detected chemical, such as boron or copper, to the 

formulation. In this case, the addition of low concentrations 

of boron in the form of boric acid or sodium borate (for

example, borax, disodium octaborate tetrahydrate) is

recommended because of the availability and water 

solubility of borates.

Table 13—Summary of the corrosion visual inspection 

after the 8-week exposure

Condition Preservative

No visible corrosion ZnN

Only white rust visible CuC

Red rust on surface, no deposits 

on wood

Water

Red rust on surface, slight deposits 

on wood

AzI, Cu8-2, CuN, pCuA-2

Red rust on surface, heavy deposits 

on wood

pCuA-1, sCuA, Cu8-1
Evaluation of Nonpressure Wood Preservatives for Military Applications

21

However, verifying the concentration of the treatment 

solution is more complex than verifying the presence of a 

preservative on a wood surface. In the pressure-treatment

industry, x ray fluorescence analyzers are used for routine 

analysis of copper in treating solutions, but these devices are 

relatively costly compared with the colorimetric indicator 

kits. It may be more practical to have treatment solution 

concentrations periodically analyzed by the preservative 

manufacturer using one of the test methods standardized by 

AWPA (Table 15). There are also private and university 

laboratories that can assay liquid samples for copper on a 

fee basis.

Results and Discussion, Green 

Preservatives

Decay Testing

Overall, the green preservative formulations tested were 

largely ineffective in protecting Southern Pine against attack 

from brown-rot fungi, allowing weight losses similar to 

those observed for specimens treated only with water 

(Fig. 18a). The lack of efficacy was also visually apparent, 

especially for Southern Pine specimens exposed to 

P. placenta (Fig. 19). A similar pattern was observed for 

yellow-poplar exposed to white-rot fungi (Fig. 18b). One of 

the treatments, Deck WR, did appear to lessen weight loss 

caused by the fungus I. lacteus, despite not making any 

claims regarding antifungal activity. Application method, 

which was examined in two of the treatments (Cedar and 

LiqSil), appeared to have little to no effect on preservative 

efficacy. In the nongreen preservatives selected for 

comparison, results showed that 0.5% AzI was the most 

effective formulation against both white- and brown-rot 

fungi, followed by the 3% ZnN formulation. Interestingly, 

performance of ZnN against P. placenta was highly 

variable, with two replicates having no weight loss and three 

replicates having substantial weight loss.

Termite Testing

As was observed for decay testing, the green preservatives 

selected for termite testing were not effective in protecting 

Southern Pine specimens from attack. Yellow-poplar 

specimens were less attacked overall, which is probably the 

Table 14—Indicators available for verifying treatment of dipped 

wood packaging materials

Preservative Type of indicator

Ingredients used in 

indicator

Cu8-1, Cu8-2 1-(2-pyridylazo)-2-napthol 

(PAN)

PAN, methanol

AzI Curcumin–salicylic acid

(requires addition of at least 

0.033% elemental boron to 

treatment solution)

Curcumin, ethanol, salicylic 

acid, hydrochloric acid

CuC, pCuA-1, sCuA, 

pCuA-2, CuN

Chrome azurol-S Chrome azurol-S, sodium 

acetate, water

ZnN Dithizone Dithizone 

(diphenylthiocarbazone), 

methyl ethyl ketone or 

chloroform

Figure 17. Color change imparted to Southern Pine sapwood after immersion in treatment formulations. Water treatment 

(bottom right) included for comparison.
Research Paper FPL–RP–693

22

result of wood species preference rather than difference in 

treatment. Two green treatments (Polymer and Deck WR) 

did show some termite resistance in Southern Pine 

specimens in terms of weight loss but still allowed

substantial feeding on the blocks (Fig. 20). As noted for 

decay, the Deck WR product also did not claim any termite 

resistance properties but still appeared to provide somewhat 

greater termite protection than the other green formulations,

which did claim to have preservative properties.

Statistical Analysis

The distribution of percentage weight losses associated with 

decay and termite attack are shown in Figures 21 and 22, 

respectively. In some cases, the variability in weight losses 

within treatment groups varied substantially (see ZnN

specimens exposed to P. placenta, for example).

One-way analyses of variance with treatment as the factor 

(at 11 levels) were carried out on percentage weight loss.

These analyses were conducted separately for each wood 

species–test organism combination. Multiple pairwise 

comparisons were adjusted based on the Tukey-Kramer 

method in SAS, with adjusted p-values <0.05 considered 

significant. Responses for some of the treatment groups 

(Southern Pine–Postia and yellow-poplar–Trametes) 

exhibited heterogeneity, and nonconstant variance models 

were used to improve model fits in those cases. The 

nonconstant variance models resulted in some nonconstant 

group difference standard errors. Therefore, mean 

separations in those cases may not be fully represented by 

simple letter connections, and SAS’s conservative 

representation is used with footnotes giving exceptions 

(Tables 16 and 17) (Westfall and others 2011).

Table 15—Analysis methods for verifying solution 

concentration standardized by the American Wood 

Protection Association (AWPA 2017)

Active ingredients and preservatives AWPA standard

Azoles (AzI, pCuA-1, sCuA, pCuA-2) A28, A31, or A48

Boron (AzI indicator additive) A21

Copper (CuC, pCuA-1, sCuA, pCuA-2, 

CuN)

A21

Imidacloprid (AzI) A43 or A48

Napthenic acid (CuN, ZnN) A41

Zinc (ZnN) A21

Figure 18. Average percentage weight losses for treated 

(a) Southern Pine and (b) yellow-poplar specimens 

exposed to brown- or white-rot fungi. Error bars show 

plus or minus one standard error.

Figure 19. Appearance of Southern Pine specimens 

treated by 1-min dip and exposed to the brown-rot 

fungus P. placenta. Each row shows the five replicate 

specimens in that treatment group.
Evaluation of Nonpressure Wood Preservatives for Military Applications

23

For Southern Pine specimens exposed to brown-rot fungi, 

weight losses from specimens treated with the various green 

preservatives tested were rarely different from the water 

controls (Table 16). The exceptions were the Polymer and 

Deck WR treatments exposed to P. placenta (see also 

footnote, Table 16). All the green treatments allowed 

significantly greater weight loss than the 3% ZnN and

0.5% AzI reference treatments, with the exception of ZnN

blocks exposed to P. placenta. This latter finding, however,

is probably the result of the relatively high and quite 

variable weight losses observed with ZnN blocks within this 

test group (Fig. 21).

For yellow-poplar specimens exposed to white-rot fungi, the 

green preservatives generally did not provide significantly 

greater protection than water (Table 17). The exception was 

Deck WR, which did have significantly lower weight losses 

than water controls in specimens exposed to I. lacteus. Both 

0.5% AzI and 3% ZnN provided significantly greater 

protection than the green preservatives for I. lacteus, even 

though ZnN sustained substantial weight loss. Comparisons

among the treatments exposed to the fungus T. versicolor, 

however, were more complicated; none of the green 

preservatives were significantly different from 0.5% AzI,

despite the much lower average weight loss with AzI. This 

result again reflects how increased variability among

replicates can obscure treatment differences (Fig. 21). ZnN

did provide significantly greater protection than most of the 

green preservatives with the exceptions of Deck WR and

Mineral-2 (see Table 17 footnote for additional significant 

differences).

The only example of a green preservative treatment 

providing significantly greater termite protection than the 

water control was Polymer applied to Southern Pine 

specimens (Table 18). The 0.5% AzI treatment was 

significantly more effective than all the green preservatives 

in both wood species, whereas ZnN was significantly more 

effective than all the green preservatives in Southern Pine 

treated blocks. For yellow-poplar, ZnN was also 

significantly more effective than all the green treatments, 

with the exceptions of Deck WR and Cedar (1-min dip).

Overall, the relative lack of efficacy observed in the green 

preservatives selected for this study indicates that they will 

not provide biological protection across the wide range of 

exposure conditions that might be encountered by WPMs. 

In addition, manufacturers of these green preservatives are 

not required to identify or quantify active ingredients used 

in the formulations, which was the case with most of the

products evaluated in this study. This latter characteristic 

could make it difficult to develop specifications for using

green preservatives and/or to conduct inspections to 

determine if WPMs are being adequately treated.

Figure 20. Average percentage weight losses for treated 

Southern Pine (blue) or yellow-poplar (green) specimens 

exposed to subterranean termites. Error bars show plus or 

minus one standard error.

Figure 21. Distribution of percentage weight loss observed 

for each treatment–wood species–decay fungus 

combination.

Figure 22. Distribution of percentage weight loss for each 

treatment–wood species combination after termite testing.
Research Paper FPL–RP–693

24

The results of this study do not preclude the possibility that 

future green preservatives could provide adequate protection 

of WPMs, because it is possible to increase the durability of 

wood products without the use of EPA-registered pesticides. 

For example, as noted in the Introduction, pressure 

treatment with high loadings of paraffin did substantially 

increase the durability of test stakes exposed in Mississippi. 

Cedar extracts have also been reported to have some 

efficacy against termites and decay, although that was not 

observed in this study, perhaps because the actives 

concentration was too low.

During the initial testing of EPA-registered preservatives,

AzI was evaluated at a single (1.05%) actives concentration

and was assumed to be highly effective against all 

Table 16—Tukey mean comparisons for Southern Pine 

specimens exposed to two brown-rot fungi (Within a 

column, means that do not share the same letter are 

significantly different (adjusted p-value of <0.05))

Treatment

Gloeophyllum trabeum Postia placentaa

LS mean 

estimate (SE)

Tukey mean 

comparison

LS mean 

estimate (SE)

Tukey mean 

comparison

AzI 0.71(2.8028) A 6.07(2.1723) A

Deck WR 44.45(2.8028) C 56.06(0.5618) B

Mineral-2 52.49(2.8028) CD 61.11(1.3194) B

Mineral-1 47.53(2.8028) CD 63.12(0.9486) B

Polymer 55.81(2.8028) CD 59.16(1.1832) B

Cedar 

30+30

56.98(2.8028) CD 63.11(0.9735) B

Cedar 

MinDip

51.71(2.8028) CD 65.27(1.4653) B

LiqSil 

Brush

51.29(2.8028) CD 64.71(1.0717) B

LiqSil 

MinDip

51.47(2.8028) CD 65.31(1.0979) B

Water 58.49(2.8028) D 66.59(0.9312) B

ZnN 26.36(2.8028) B 32.57(12.9668) AB

a

Modeled with heterogeneous variance for each treatment group (based on 

results from Levene’s HOV test). This Tukey column does not reflect all 

significant comparisons. Because of lower variances for some groups, the 

following additional pairs are significantly different for Postia: (water–

polymer), (water–Deck WR), (LiqSil MinDip–Deck WR), (Cedar MinDip–

Deck WR), (LiqSil Brush–Deck WR), (Mineral-1–Deck WR), (Cedar 30+30–

Deck WR).

Table 17—Tukey mean comparisons for yellow-poplar 

specimens exposed to two white-rot fungi (Within a 

column, means that do not share the same letter are 

significantly different (adjusted p-value of <0.05))

Treatment

Irpex lacteus Trametes versicolora

LS mean 

estimate (SE)

Tukey mean 

comparison

LS mean 

estimate (SE)

Tukey mean 

comparison

0.5% AzI 0.22(3.5000) A 12.85(6.6341) A

Deck WR 9.51(3.5000) A 31.60(2.7008) AB

Mineral-2 66.88(3.5000) C 34.37(2.6974) AB

Mineral-1 62.40(3.5000) C 35.43(2.7038) AB

Polymer 60.91(3.5000) C 42.54(4.1107) ABC

Cedar 

30+30

61.09(3.5000) C 42.66(1.7616) BC

Cedar 

MinDip

63.73(3.5000) C 40.69(2.8659) ABC

LiqSil 

Brush

75.14(3.5000) C 46.70(2.8358) BC

LiqSil 

MinDip

76.35(3.5000) C 47.34(0.9196) C

Water 64.11(3.5000) C 44.21(3.1392) BC

ZnN 36.38(3.5000) B 20.49(2.2066) A

a

Modeled with heterogeneous variance for each treatment group (based on 

results from Levene’s HOV test). This Tukey column does not reflect all 

significant comparisons. Because of lower variances for some groups, the 

following additional pairs are significantly different for Trametes: (Polymer–

ZnN), (CedarMinDip–ZnN), (Mineral-1–ZnN).

Table 18—Tukey mean comparisons for Southern Pine and yellow-poplar 

specimens exposed to termites (Within a column, means that do not share the 

same letter are significantly different (adjusted p-value of <0.05))

Treatment

Southern Pine Yellow-poplar

LS mean estimate (SE)

Tukey mean 

comparison LS mean estimate (SE)

Tukey mean 

comparison

AzI 0.09(1.7198) A 0.75(1.8025) A

Deck WR 15.92(1.7198) BC 11.54(1.8025) BC

Mineral-2 26.37(1.7198) D 16.14(1.8025) C

Mineral-1 25.78(1.7198) D 15.33(1.8025) C

Polymer 11.54(1.7198) B 17.45(1.8025) C

Cedar 

30+30

29.19(1.7198) D 16.24(1.8025) C

Cedar 

MinDip

23.87(1.7198) CD 10.87(1.8025) BC

LiqSil 

Brush

27.22(1.7198) D 17.51(1.8025) C

LiqSil 

MinDip

26.67(1.7198) D 17.31(1.8025) C

Water 23.28(1.7198) CD 13.02(1.8025) C

ZnN 2.38(1.7198) A 4.17(1.8025) AB
Evaluation of Nonpressure Wood Preservatives for Military Applications

25

organisms tested. This result suggested that a lower actives 

concentration might be adequate. During a subsequent study 

to determine the effect of laser marking on decay and 

termite resistance, a 0.5% concentration was evaluated 

(Arango and others 2016). Although the 0.5% AzI 

concentration did appear to be effective in the laser-marking 

research, several aspects of that test method differed 

considerably from the standard method used to evaluate the 

1.05% AzI concentration. Thus, 0.5% AzI was evaluated as 

a positive control in the green preservative testing, using 

methods similar to those used in evaluating the 1.05% 

concentration. Results showed the 0.5% AzI to be highly 

effective in preventing decay in Southern Pine specimens 

exposed to the brown-rot fungus G. trabeum and in yellowpoplar specimens exposed to the white-rot fungus I. lacteus. 

It was also highly effective against termites in both wood 

species. However, it did allow slight weight loss by 

P. placenta in Southern Pine specimens and somewhat 

greater weight loss by T. versicolor in yellow-poplar. In 

contrast, the 1.05% concentration evaluated in the initial 

study allowed no measureable weight loss by any of the test 

fungi or termites in either wood species. Thus, although the 

0.5% AzI concentration was effective, the effectiveness of 

even lower concentrations is not well supported by the data.

Summary and Recommended 

Applications

None of the green preservatives evaluated under the 

conditions of this study appeared suitable for protection of 

WPMs. However, several of the EPA-registered test 

formulations provided protection from fungal attack that 

was at least equivalent to that provided by current 

formulations. AzI was effective at both 0.5% and 1.05% 

concentrations, and pCuA-1 (2.0% Cu), sCuA (2% Cu), and

pCuA-2 (1% and 2% Cu) were also shown to be effective

alternatives. Although the 2% CuC formulation was highly 

vulnerable to copper-tolerant P. placenta, this formulation 

was effective against the other fungi evaluated. Variability 

observed between blocks exposed to P. placenta influenced 

interpretation of efficacy for some other copper 

formulations as well, but the actual risk of copper tolerance 

for WPMs in field settings remains unknown. In termite 

testing, only two test formulations (AzI and 2% sCuA) did 

not have significantly greater weight loss than the reference 

preservative CuN. However, higher concentrations of 

several other test formulations did protect at least as well as 

the ZnN and Cu8 reference preservatives.

Corrosion testing revealed that all of the test formulations,

except CuC, were substantially more corrosive than ZnN.

The copper concentration in CuC was similar to other 

preservatives tested, and it is unclear why this preservative 

exhibited such a low amount of corrosion. The percentage

weight loss of pCuA-2, sCuA, and CuN increased linearly 

with time, indicating the corrosion rate was constant through 

the 8-week test. This suggests that these preservatives may 

actually have an increased likelihood of causing corrosion 

because the corrosion rate was not decelerating with time.

The results from the laboratory fungal, termite, and 

corrosion testing in this study were used to develop a 

relative protection index for the test formulations, as well as 

recommended applications and criteria for evaluating future 

formulations (Appendix). The severity of laboratory fungal 

and termite tests may vary depending on vigor of the test 

organisms. To help account for this biologic variability, the 

weight losses observed with preservative-treated specimens 

were divided by those of their respective untreated controls.

The suitability of preservative formulations for WPM 

applications was then based on the resulting 

treated/untreated weight loss ratios and on the weight losses 

observed in corrosion testing. As part of this process, it was 

recognized that desirable preservative characteristics may 

vary depending on the type of WPM. Corrosion is 

particularly a concern for wire-bound boxes, whereas decay 

and insect resistance is of greatest concern for WPMs that 

are likely to be placed in contact with the ground. U.S.

Army personnel created three classifications of WPM–

preservative combinations to allow greater flexibility in 

matching the characteristics of the preservative to the 

expected exposure condition of the WPM. The suitability 

criteria for these three classifications are

Type I — preservatives for all WPMs must meet these 

conditions:

Weight loss caused by corrosion test must be less 

than 3%.

Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.0.

No ratio for any single decay or termite test can 

exceed 0.4.

Type II — preservatives for wire-bound boxes only must 

meet these conditions:

Weight loss caused by corrosion test must be less than

0.75%.

Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.25.

No more than one ratio for an individual decay or 

termite test can exceed 0.2.

Type III — preservatives for all WPMs except wire-bound 

boxes must meet these conditions:

Weight loss caused by corrosion test may exceed 3%.

Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.0.

No ratio for any single decay or termite test can 

exceed 0.4.

Not suitable — preservatives that do not meet the criteria 

for Type I, II, or III are not suitable for treatment of WPMs.
Research Paper FPL–RP–693

26

Table 19 shows the results of applying these criteria to the 

formulations evaluated in this study.

AzI and six of the more concentrated copper formulations 

were classified as Type I (suitable for all WPMs). Despite a 

single high weight loss ratio with the fungus P. placenta, 

2% CuC was judged to be suitable for wire-bound boxes 

because of its desirable corrosion properties. In contrast, the 

2% sCuA formulation was judged unsuitable for wire-bound 

boxes because of its corrosiveness but suitable for other 

applications because of its efficacy against decay and 

termite attack. Future candidate preservatives may 

potentially be evaluated using the methods and criteria 

described in the Appendix. Based on the results of this 

study, U.S. Army personnel developed a drawing (similar to 

a specification) that covers dip preservative treatment of all 

wood products used for a wide range of applications (U.S. 

Army 2017a). A separate source control drawing lists 

approved sources of supply and details the tests and criteria 

that must be used to qualify future preservatives (U.S. Army 

2017b).

Table 19—Weight loss ratios and wood packaging materials (WPMs) suitability assignmentsa (factors key to the WPM 

assignment are underlined and in bold)

Preservative

formulation

Corrosion

categoryb

Biologic weight loss ratios, treated/untreated

WPM type

Basis for 

suitability 

assignment

Fungal Termite

Sum of

ratios

G. 

trabeum

P. 

placenta

T. 

versicolor

I. 

lacteus

Southern 

Pine

Yellowpoplar

CuC, 1% <0.75% 0.56 1.01 0.02 0.21 0.08 0.47 2.35 None High biologic 

ratios

CuC, 2% <0.75% 0.13 0.94 0.01 0.01 0.00 0.14 1.24 II only Low corrosion, 

high fungal 

ratio

AzI, 0.5% 0.75–3.0% 0.01 0.09 0.29 0.00 0.00 0.06 0.46 I

AzI 1.05% 0.75–3.0% 0.01 0.00 –0.06 –0.01 0.00 0.00 –0.06 I

pCuA-1, 1% 0.75–3.0% 0.04 0.64 –0.01 –0.01 0.10 0.66 1.43 None High biologic 

ratios

pCuA-1, 2% 0.75–3.0% 0.00 0.11 –0.01 –0.01 0.00 0.38 0.47 I

sCuA, 1% >3.0% 0.04 0.83 0.00 –0.01 0.01 0.38 1.25 None High fungal 

ratio, corrosion

sCuA, 2% >3.0% 0.01 0.05 –0.01 –0.03 0.00 0.10 0.13 III only Corrosion, low 

biologic ratios

pCuA-2, 1% 0.75–3.0% 0.00 0.09 0.04 0.00 0.02 0.58 0.72 None High termite 

ratio, corrosion

pCuA-2, 2% 0.75–3.0% 0.00 0.17 –0.01 0.00 0.02 0.22 0.40 I

Cu8-1, 1.2% 0.75–3.0% 0.00 0.04 0.45 0.46 0.22 0.71 1.89 None High biologic 

ratios

Cu8-1, 1.8% 0.75–3.0% 0.00 0.01 0.39 0.47 0.44 0.68 1.98 None High biologic 

ratios

Cu8-2, 1.2% 0.75–3.0% 0.01 0.01 0.01 0.00 0.01 0.53 0.57 None High termite 

ratio, corrosion

Cu8-2, 1.8% 0.75–3.0% 0.01 0.01 0.01 –0.01 0.03 0.33 0.38 I

CuN, 1% 0.75–3.0% 0.21 0.89 0.00 0.06 0.03 0.04 1.24 None High fungal 

ratio, corrosion

CuN, 2% 0.75–3.0% 0.01 0.11 0.00 0.01 0.00 0.00 0.13 I

ZnN, 3% <0.75% 0.18 0.08 0.23 0.29 0.08 0.14 1.00 I

a

Suitability assignments are based on information available at the time of this report and may not reflect the current use practices. These recommendations are 

not and should not be used in lieu of military specifications.

b

Corrosion category is based on the highest concentration evaluated for a formulation.
Evaluation of Nonpressure Wood Preservatives for Military Applications

27

Acknowledgments

The authors acknowledge funding from the U.S. Army 

Armament Research Development and Engineering Center

(ARDEC) and the invaluable assistance provided by Patrick 

DeWald, Mark Rehmstedt, and Jason Langel of ARDEC.

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Evaluation of Nonpressure Wood Preservatives for Military Applications

29

Appendix—Protection Index: 

Methods and Criteria for Evaluating

Candidate Preservatives

1. Corrosion testing

A. Materials

1. Both wire and wood samples used in the testing 

shall come from untreated packing crates that are 

disassembled.

2. The wire shall be cut into 150-mm-long segments.

3. The wood box shall be cut into strips that are 25 

mm wide by 175 mm long.

B. Predip wire cleaning procedure

1. The wires shall be cleaned in an ultrasonic cleaner 

with a soap solution for 5 min followed by a rinse 

under flowing deionized water. The wires shall 

then be placed in an ultrasonic cleaner for 5 min in 

deionized water.

2. The wires shall then be weighed to the nearest 

0.1 mg.

3. After weighing, the fasteners shall be attached to 

the wood strip with a nonmetallic cable tie.

C. Dip procedure

1. The wood–wire assembly shall be dipped for 60 s 

in the treatment solution. The excess treatment 

shall be blotted from the wood, and the wood shall 

be sealed in a polyethylene bag.

2. At least 10 replicates should be run.

3. In addition to the treatment solution, 10 additional 

samples shall be dipped into deionized water, 

blotted dry, and sealed in a polyethylene bag.

These are the water control samples.

D. Exposure

1. The wood–wire assemblies shall remain sealed in a 

polyethylene bag for 8 weeks. The bags shall be 

placed in a high humidity environment (>90% RH) 

that is maintained at 27 °C.

E. Postexposure procedure

1. The wire shall be separated from the wood by 

destroying the plastic cable tie.

2. The corrosion products of the wire shall be 

removed.

a. The wire shall be placed in an ultrasonic 

cleaner in a solution of 50 vol% water and 

50 vol% EvapoRust (Orison Marketing, 

Abilene, Texas) for 60 min.

b. After being removed from the bath, the 

wires shall be wiped with a paper towel 

and allowed to air-dry.

3. The wires shall be weighed to the nearest 0.1 mg.

F. The percentage weight loss shall be calculated as





 



 − = initial

initial final Percentage weight loss 100

m

m m

2. Laboratory decay resistance testing

Testing shall be conducted in accordance with the most 

recent version of AWPA Standard E10 (AWPA 2017) with 

the following additional specifications:

A. The wood species used shall be the sapwood of 

Southern Pine and yellow-poplar.

B. Preservative shall be applied by immersing the 

specimen(s) in the treatment solution for 1 min at 

atmospheric pressure. If necessary, the treatment 

vessel shall be agitated to ensure homogenous

concentration of active ingredient within the vessel.

C. The weathering (leaching) method after preservative 

treatment will deviate from the standard method in 

that

(i) specimens shall not be vacuum-impregnated with 

leaching water, and

(ii) the total duration of leaching shall be 7 days 

(168 h) with water changes after 6, 24, 48, and 

96 h.

D. Specimen dimensions shall be 19 by 19 by 19 mm.

E. Only one specimen shall be placed into each bottle.

F. The fungi used for each wood species shall be

(i) Gloeophyllum trabeum (isolate Madison 617) and 

Postia placenta (isolate Madison 698) for 

Southern Pine and

(ii) Trametes versicolor (isolate Madison 697) and 

Irpex lacteus (isolate Madison 517) for yellowpoplar.

G. The following ratio shall be calculated for each 

fungus–wood species combination (four total ratios):

Average weight loss of preservative-treated 

specimens/Average weight loss of untreated 

specimens

3. Laboratory termite resistance testing

Testing shall be conducted in accordance with the most 

recent version of AWPA Standard E1 (AWPA 2017) with 

the following additional specifications:

A. The single-choice (no-choice) procedure shall be 

used.

B. The wood species used shall be the sapwood of 

Southern Pine and yellow-poplar.
Research Paper FPL–RP–693

30

C. Preservative shall be applied by immersing the 

specimen(s) in the treatment solution for 1 min at 

atmospheric pressure. If necessary, the treatment 

vessel shall be agitated to ensure homogenous 

concentration of active ingredient within the vessel.

D. The weathering (leaching) method after preservative 

treatment will deviate from the standard method in that

(i) specimens shall not be vacuum-impregnated with 

leaching water, and

(ii) the total duration of leaching shall be 7 days 

(168 h) with water changes after 6, 24, 48, and 96 h.

E. The following ratio shall be calculated for each wood 

species (two total ratios):

Average weight loss of preservative-treated 

specimens/Average weight loss of untreated 

specimens

4. Suitability determination

Suitability for WPMs shall be assigned based on the weight 

loss from corrosion testing (Note 1) and from the weight 

loss ratios calculated from decay and termite testing (Notes 

2 and 3):

-Type I (all WPMs) must meet these conditions:

A. Weight loss caused by corrosion test must be 

below 3%.

B. Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.0.

C. No ratio for any single decay or termite test can 

exceed 0.4.

-Type II (wire-bounds only) must meet these conditions:

A. Weight loss caused by corrosion test must be 

below 0.75%.

B. Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.25.

C. One and only one ratio for an individual decay 

or termite test can exceed 0.2.

-Type III (all WPMs except wire-bound boxes) must meet 

these conditions:

D. Weight loss caused by corrosion test may be

3% or more.

E. Sum of the six ratios calculated from decay and 

termite tests cannot exceed 1.0.

F. No ratio for any single decay or termite test can 

exceed 0.4.

-Not suitable: Preservatives that do not meet the criteria 

for Type I, II, or III are not suitable for treatment of 

WPMs.

5. Validation of test conditions

G. Average corrosion weight losses in watertreated controls shall be between 2% and 3%.

H. Average fungal weight losses in water-treated 

controls shall equal or exceed 40% for each 

fungus–wood species combination.

I. Average termite weight losses in untreated 

control specimens shall equal or exceed 20% 

for each wood species evaluated.