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A METHOD FOR THE PREVENTION OF WOOD DECAY FROM NAIL PENETRATION.

DIAN-QING YANG [*]

ABSTRACT

Wood often fails in structures due to decay around nail fastenings. Nails may penetrate the wood treated zone and bring fungal spores into the wood where the preservative has not reached. Nails trap water and will elevate the wood moisture content around them, creating a suitable environment for fungal growth. The objective of this research was to provide a simple and economic process for treating nail holes that pass through the treated zone of wood. This paper provides a process to seal the broken surface of the wood with a product containing a wood preservative of 2 percent by weight of chromated copper arsenate in grease, thereby preventing wood decay around the nails.

Many wood structures in buildings, such as stairs, frames, sheathing, and balconies, as well as structures used in public parks fail much earlier than they were designed to. These failures are most often attributed to wood decay. Most of these structures use preservative-treated wood, and are supposed to be decay resistant. It is well known that most of fungal infections start from cuts, holes, or injuries caused by saws, nails, or spikes that penetrate the treated zone. Therefore, the American Wood-Preservers' Association published a standard for the care of preservative-treated wood products [2]. Standard M4-96 requires that "all cuts, holes and injuries such as abrasions, nail and spike holes which may penetrate the treated zone shall be field treated" (M4-96, 1.5.1) [2]. The standard also states that "preservative field treatment shall be applied in accordance with the product label. The application method shall coat any surface exposed by damage or field fabrication while not using excess preservative" (M4-96, 1.5.3) [2]. Most cuts and significant openings are field treated by brushing on a wood preservative, such as copper naphthenate. However, there is no method of application for treating nail and spike holes and they are often left untreated. Nails may penetrate the wood treated zone and bring fungal spores into the wood where the preservative has not reached. Nails trap water and will elevate the wood moisture content around them, creating a suitable environment for fungal growth and nail corrosion. Therefore decay, in some cases, first appears around the nails of the wood structure [6].

The growth of decay fungi in wood fosters the corrosion of iron and steel nails as these fungi bring more water into the wood [5,6]. In the decay process, as wood loses strength, the nail withdrawal and lateral resistance are diminished. Of course, nails also corrode in the absence of decay fungi but at a much slower rate because less water is available.

The corrosion of nails and its prevention have been studied [3]. The results indicated that nail corrosion could be avoided by keeping water out of the joints, or by using non-corroding nails. Galvanized nails (zinc-coated) are most commonly used where corrosion resistance is required [4]. However, corrosion-resistant nails or coated nails do not prevent decay of the wood around them.

This paper proposes a product and a method to be used in the treatment of nail holes that substantially reduces the threat of wood decay.

MATERIALS AND METHODS PREPARATION OF PRESERVATIVE GREASE AND THE NAIL TREATMENT

The preservative grease was prepared by mixing a commercial wood preservative, chromated copper arsenate (CCA) (Chemical Specialties Inc., Charlotte, N.C.) with a carrier, DOW Corning high-vacuum grease (DOW Corning Corp., Midland, Mich.); 4 g of 50 percent concentrated CCA Type C were added to 96 g of the grease and mixed thoroughly with a blender. The appearance of the final product was a grease of yellow color.

Jack pine sapwood was cut into wafers 55 by 20 by 5 mm. These wafers were conditioned in a forced-draft oven set at 60[degrees]C to a constant moisture equilibrium and were weighed. The nails used in the test were common round iron nails with flat heads, which were 3/4-inch (19-mm) long and 1 mm in diameter. Each nail was weighted and dipped to half its length in the CCA grease before being thoroughly nailed into a wood wafer. Each wafer contained two nails situated in the middle of its width and 25 mm apart (Fig. 1). After nailing, each wafer was immediately weighed to determine the take up of the CCA grease. A second group of wafers was nailed with nails dipped in a clear grease without the addition of CCA in the same manner as just described. A third group of wafers was nailed with ungreased nails to serve as controls.

EFFECTIVENESS TESTING ON WOOD WAFERS

The following decay fungi were used in the test: white-rot, Coriolus versicolor (ATCC 12679) and Irpex lacteus (ATCC 11245); and brown-rot, Gloeophylum trabeum (ATCC 11539) and Postia placenta (ATCC 11538).

All fungal cultures were maintained on 2 percent malt extract agar (20 g malt extract and 20 g Difco agar in 1 L distilled water) at 5[degrees]C. Cultures were transferred onto the same freshly prepared medium in Petri plates and incubated at 25[degrees]C for 2 weeks before being used in the experiment.

A modified procedure of a standard soil block test defined in the American Wood-Preservers' Association Standard E10-91 (1) was used to evaluate the efficacy of the protection of wood against decay. Soil (250 g) was placed in glass jars, and distilled water was added to bring the moisture content of the soil to 30 percent by weight. Two feeder strips of jack pine (34 by 28 by 3 mm) were placed on top of the soil in each jar. The jars were autoclaved at 121[degrees]C for 30 minutes, twice within a 24-hour interval. The feeders in each jar were inoculated with one of the four test fungi. The jars were incubated 2 weeks in a growth chamber set at 26[degrees]C before being used for the experiment.

Test wafers were steamed at 100[degrees]C for 20 minutes in beakers containing a filter paper soaked with 5 mL of water, covered with aluminum foil. After cooling, these test wafers were placed in the soil bottles aseptically, nailhead facing down, making contact with the mycelium-covered feeder strips. Two wafers were added to each bottle, so each treatment contained 10 wafers placed in 5 bottles. The culture bottles of wood wafers were incubated for 16 weeks in a growth chamber set, at 26[degrees]C and 75 percent relative humidity. At the end of the incubation, wafers were removed from the bottles, cleaned of the attached fungal mycelia, and rated for decay development around the nails, based on a visual rating index: 0 = no decay around nails; 1 = light surface decay around nails; 2 = moderate decay around nails; 3 = heavy decay around nails, which become loose or fall out.

COMPRESSION TEST ON WOOD WAFERS

After the wood wafers were visually rated, they were put in an oven at 50[degrees]C and dried to a constant weight. They were then subjected to a compression test for nail withdrawal resistance. The testing machine used a 250 N load cell (Fig. 1). A force was applied to each nail tip in order to push the nail down a distance of 8 mm. The maximal load (N) on each nail was recorded. An average of 20 measurements in each treatment was calculated and used for measuring the effectiveness of the treatment against decay.

DATA ANALYSIS

Data were subjected to analysis of variance (ANOVA) using the statistical analysis system (SAS) (7). Following ANOVA, the individual means were compared using Scheffe's test for multiple comparison (7).

RESULTS AND DISCUSSION

The results showed that in the CCA grease treatment group, the average weight of wood wafers was about 2.89 g, and the average weight of nails was 0.2 g. The minimal take up of CCA grease by each nail was 0.011 g, the maximal take up of CCA grease was 0.031 g, and the average take up of CCA grease was 0.019 g.

The efficacy test of the product against decay is shown in Figure 2 and Table 1. The incidence of wood decay around nails dipped in CCA grease was significantly lower than those dipped in grease alone or untreated nails. The two brown-rot fungi, G. trabeum and R placenta, grew vigorously on wood wafers. The average visual wood decay indices around untreated nails reached 2.00 and 2.95 from the colonization of these two fungi, respectively. In the case of nails dipped in CCA grease, the decay indices dropped to 0.10 and 1.35, respectively. The wood decay indices around nails dipped in the grease alone were similar to those of untreated controls.

The compression test on wood wafers is shown in Table 2. Nails dipped in CCA grease were more resistant to withdrawal from wafers than untreated nails or nails dipped in grease alone after exposure to the white-rot fungi C. versicolor or I. lacteus. For example, 28.44 N was required to withdraw an untreated nail from a wafer exposed to C. versicolor, whereas a nail dipped in CCA grease and exposed to a same fungus required 88.03 N. There was no load difference found in the withdrawal of untreated nails and nails dipped in grease alone.

These results show that CCA in grease is effective against decay around nail fastenings. Rainwater is often trapped by nails or is found at the junction of wood pieces, providing favorable conditions for nail corrosion and fungal infection [6]. The grease in this product may prevent water access into the wood around nails, thus preventing the corrosion of nails. The CCA in the product may kill the wood-damaging fungi brought into wood through nail penetration. However, our test was a laboratory accelerated test that only lasted 4 months. A field application may be required to determine the effective duration of the product.

Since CCA is the most common wood preservative used in North America, we selected it as our working model. The Pest Management Regulatory Agency in Canada had withdrawn the registration of CCA as a field-applied preservative a long time ago because of its toxicity. However, it is expected that any wood preservative will work when mixed with grease and applied to nail holes in a similar manner as described in this paper. Copper or zinc naphthenates are more appropriate preservatives to use in the field. Both are registered for field applications and both will dissolve in grease.

This product was designed to use principally for nails or spikes that penetrate the wood, treated or untreated. However, the product may also be applied to checks in the wood where the likelihood of fungal infection is as important as nail holes. Further tests on this application may be necessary.

CONCLUSION

This paper provides an effective method of preventing or inhibiting wood decay around nails using a product containing 2 percent by weight of CCA in grease. It also provides a method of application of the product into nail holes of a wood structure. Nails are dipped half of their length in the CCA grease and nailed into wood. In the laboratory test, the area of wood around untreated nails was well colonized by the four decay fungi tested. In the case of nails dipped in CCA grease, the decay indices were much lower. The degree of wood decay around nails dipped in the grease alone was similar to those of untreated controls. The method described in this paper can be used to treat any wood fastenings such as nails, spikes, or staples. The combination of any suitable fungicide or wood preservative with a grease carrier will likely be as effective.

The author is a Research Scientist, Forintek Canada Corp., Eastern Lab., Sainte-Foy, QC, Canada G1P 4R4. Forintek Canada Corp. would like to thank its industry members, Natural Resources Canada (Canadian Forest Serv.), and the provinces of British Columbia, Alberta, Quebec, Nova Scotia, New Brunswick, and Saskatchewan for their guidance and financial support of this research. The author would like to thank Sylvain Mercier and Francine Cote for their assistance on the experiments and Paul Morris for his critical review of the manuscript. This paper was received for publication in April 2000. Reprint No. 9115.

(*.) Forest Products Society Member.

[c] Forest Products Society 2001.

Forest Prod. J. 51(4):67-70.

LITERATURE CITED

(1.) American Wood-Preservers' Association. 1991. Standard method of testing wood preservatives by laboratory soil-block cultures. AWPA Standard E10-91:1-11. AWPA, Granbury, TX.

(2.) _____. 1996. Standard for the care of preservative-treated wood products. AWPA Standard M4-96:248-249. AWPA, Granbury, TX

(3.) Baker, A.J. 1992. Corrosion of nails in CCA- and ACA-treated wood in two environments. Forest Prod. J. 42(9):39-41.

(4.) Canadian Standards Association. 1974. Wire nails, spikes and staples. CSA Standard B111-1974:1-34. GSA, Rexdale, ON, Canada.

(5.) Gjovik, L.R. and R.H Baechler. 1977. Selection, production, procurement and use of preservative-treated wood. Gen. Tech. Rept. FPL-15. USDA Forest Serv., Forest Prod. Lab., Madison, WI.

(6.) Kubler, H. 1992. Corrosion of nails in wood construction interfaces. Forest Prod. J. 42(1):47-49.

(7.) SAS Institute Inc. 1989. SAS/STAT User's Guide. 6th ed. SAS Inst. Inc., Cary, NC.
 Index of wood decay around nails. [a]
Treatment G. trabeum P. placenta
2% CCA grease 0.10 [+ or -] 0.21 A 1.35 [+ or -] 0.41 A
Grease alone 1.80 [+ or -] 1.09 B 2.90 [+ or -] 0.21 B
Untreated 2.00 [+ or -] 0.85 B 2.95 [+ or -] 0.16 B
Treatment C. versicolor I. lacteus
2% CCA grease 0.10 [+ or -] 0.21 A 0.15 [+ or -] 0.34 A
Grease alone 1.50 [+ or -] 0.58 B 1.75 [+ or -] 0.49 B
Untreated 1.65 [+ or -] 0.67 B 1.55 [+ or -] 0.50 B


(a.)Values are shown as means of 20 replications [+ or -] standard deviations. Values in each column followed by the same capital letter are not significantly (p = 0.05) different according to Scheffe's test following ANOVA. Visual rating index: 0 = no decay around nails; 1 = light surface decay around nails; 2 = moderate decay around nails; 3 = heavy decay around nails, which become loose or fall out.
 Compression test for nail withdrawal
 from wood wafers. [a]
Treatment G. trabeum P. placenta
 (N)
2% CCA grease 63.74 [+ or -] 44.69 A 22.43 [+ or -] 16.90 A
Grease alone 24.09 [+ or -] 8.41 B 14.20 [+ or -] 8.38 AB
Untreated 44.31 [+ or -] 35.14 AB 8.31 [+ or -] 5.44 B
Treatment C. versicolor I. lacetus
2% CCA grease 88.03 [+ or -] 29.38 A 93.94 [+ or -] 26.30 A
Grease alone 36.82 [+ or -] 14.76 B 26.67 [+ or -] 16.57 B
Untreated 28.44 [+ or -] 9.78 B 36.96 [+ or -] 18.52 B


(a.)Values are shown as means of 20 replications [+ or -] standard deviations. Values in each column followed by the same capital letter are not significantly (p = 0.05) different according to Scheffe's test following ANOVA.
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Author:YANG, DIAN-QING
Publication:Forest Products Journal
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Apr 1, 2001
Words:2499
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