Technical Field

The present invention relates to preservatives and particularly preservatives for wood materials. Background of the Invention

Wood continues to be one of the most commonly used raw materials for Framing and exterior construction. Susceptibility to insect, termite and fungal attack in some countries has been overcome by treatment of wood. Application methods and approved chemicals vary dramatically throughout the world. Softwood timbers, including pinus radiata, pinus elliotti, and pinus carribea and hardwood timbers, including eucalyptus species are used as building timber in Australia. These species, along with others, are susceptible to insect, termite and fungal attack. Wood can be used as solid wood, either sawn or roundwood or be converted in engineered wood products like plywood, laminated veneer lumber (LVL) or oriented strand board (OSB). Wood from solid wood production and engineered wood products need protection from insects, termites and fungal attack.

Many countries including Australia, New Zealand and the USA are struggling to find suitable cost-effective and environmentally acceptable methods to combat this ever- increasing risk of insect, termite and fungal attack. In Australia, for example, treatment of timber is covered by the Australian standard

AS 1604.1-2005 which states:

"All preservative-treated wood shall show evidence of distribution of the preservative in the penetration zone in accordance with the following requirements:

(a) If the species of timber used is of natural durability class 1 or 2, the preservative shall penetrate all the sapwood. Preservative penetration of the heartwood is not required.

(b) If the species of timber used is of natural durability class 3 or 4, the preservative shall penetrate all of the sapwood and, in addition one of the following requirements shall apply.

(i) Where the lesser cross-sectional dimension is greater than 35 mm, the penetration shall be not less than 8 mm from any surface. Where the lesser cross-sectional dimension is equal or less then 35 mm, the penetration shall be not less than 5 mm from any surface, (ii) Unpenetrated heartwood shall be permitted, provided that it comprises less than 20% of the cross-section of the piece and does not extend more than halfway through the piece from one surface to the opposite surface and does not exceed half the dimension of the side in the cross-section on which it occurs."

In order to provide for penetration of the preservative, a carrier must be used. As shown in the Australian standard, the carriers currently available are waterborne or solvent borne systems.

Waterborne carriers swell wood and hence may need to be re-dried prior to use in service.

The process sequence is:

Dry wood -> treat -^ re-dry wood Solvent borne preservatives, because they are non-polar, do not raise the moisture content and hence do not swell the wood. The process sequence is:

Dry wood -> solvent treat

The disadvantage of this treatment is the high cost of solvents and potential environmental concerns with volatile organic compounds (VOCs) being released into the atmosphere.

Prior processes for treating timber have been disclosed in our co-pending application, PCT/AUOl/01625, the contents of which are incorporated herein by reference. In that case, a self sealing envelopes which protected against damage could be produced. However, there is an ongoing need to find further improvements in wood protection which in some circumstances may provide advantages over the prior art or at least provide a commercial alternative thereto. Disclosure of the Invention hi a broad aspect, the invention provides a carrier system for impregnating wood which is capable of carrying an active ingredient throughout the wood. The carrier system comprises 0.1-30% of a drying or semi-drying oil and 70-99.9% of an extender.

According to a further aspect, the invention provides a composition for treating wood comprising: an active agent or agents; and a carrier system which comprises 0.1-30% of a drying or semi-drying oil and 70-80% of an extender.

Preferably, the active agent is present in an amount to achieve the desired treatment effect.

Preferably the active agent or agents is present in an amount up to 5 % mass/mass of the composition, more preferably an amount up to 2%, even more preferably in an amount up to 1%, even more preferably in an amount up to 0.5%. Preferably, the active agent or agents is present in a total amount of more than 0.001% of the composition, more preferably in a total amount greater than 0.01% and even more preferably in a total amount greater than 0.1% mass/mass of the composition.

Preferably, if the biocide is an IPBCs (3-iodo-2-propynyl- butylcarbamate) it is present in an amount of 0.01 to 0.05% mass/mass, more preferably 0.015% mass/mass to 0.03% mass/mass. However, IBPCs may be present in the composition in an amount as high as 0.2 to 0.6% mass/mass of the composition.

Preferably, if the biocide is tebuconazole, it is present in an amount of from 0.001% to 0.05%, and more preferably 0.004 to 0.030%. However, azoles may be present in an amount as high as 0.8% mass/mass of the composition.

Preferably, if the biocide used is a copper biocide it is present in an amount 0.01 to 0.4%, and more preferably in an amount of from 0.04 to 4%. Other preferred ranges include 0.04%-0.4% and 0.01 to 4%.

Preferably, if copper chrome arsenate (CCA) is used, it is present in an amount of from about 0.2 to 0.8% m/m, and more preferably to 0.63% m/m

In one preferred embodiment, the extender is combustible. The definition in Australia of combustible substance is one having a flash point above 60.5 ⁰ C. Preferably the extender has a flash point greater than 60.5 ⁰ C. hi an alternative preferred embodiment, the extender is flammable. Preferably, the extender has a flash point less than 60.5 ⁰ C.

Preferably, the drying oil is linseed oil. More preferably, the linseed oil is pale boiled linseed oil (PBLO)

Alternatively, the drying oil may be fish oil or any other drying oil or semi-drying oil may be used. A drying oil is an oil which saturates in air. For example, linseed oil dries to form a water barrier and penetrates without the need for pressure and advantageously is low odour.

Other suitable drying oils include tung oil, poppy oil, walnut oil, safflower oil and sunflower oil. Semi-drying oils suitable include cottonseed oil, corn oil and soybean oil.

Additionally, any oils having suitable quantities of linolenic and linoleic oil maybe used.

Preferably, the drying oil is present in an amount of 0.1 to 30% mass/mass of the carrier system, more preferably about 10-30% of the carrier system, more preferably around 10-20% of the carrier system, and even more preferably around 10-15% of the carrier system. The extender may be present in any amount to bring the drying oil and any active to 100% i.e. 70-99.9%.) The extender is preferably present in an amount of about 80% of the carrier system.

In one preferred embodiment, the extender is combustible, having a flash point greater than 60.5 ⁰ C. Extenders with high boiling point/flash point which reduce vapour emissions in production and use. Another surprising benefit of using a high boiling point carrier system is its advantageous effect on migration of the preservative. Without wishing to be bound by theory, it is believed that higher boiling point of the

carrier/preservative mixture tends to allow the preservative to move inwards, as compared with more volatile solvents which migrate outwardly.

In an alternative preferred embodiment, the extender is flammable, having a flash point less than 60.5 ⁰ C. Any extenders with suitable solvency properties, even those having very low flash points, are suitable in the present invention.

Preferably, the extender is heating oil. Other light weight hydrocarbons, such as white spirit, kerosene, high flash kerosene and oils such as diesel are suitable extenders. The term extenders as used herein also encompasses mixtures of one or more extenders, for example, mixtures of diesel and white spirit. Using a non-swelling drying carrier oil also has the advantage that the treated wood/timber does not need to be re-dried, i.e. treatment can be accomplished by simple dipping of the wood until the required level of uptake is achieved.

The treatments of the present invention can be applied both as an envelope, for example, to a depth of 5mm from the entire outside surface of the timber, or can be applied to a level of full penetration.

Preferably, the active may be a biocide, insecticide, termicide, fungicide or the like.

A wide variety of preservatives may also be used in combination with the carrier system. Various insecticides and termicides known in the art may be mixed with the oil including synthetic pyrethroid, permethrin, cypermethrin, bifenthrin, imidachloprid etc. Fungicides and mouldicides may also be used such as iodopropynylbutylcarbamate (IPBC), azoles, tributyltin naphthenate (TBTN) and the class of mouldicides known as isothiazolones.

Fungicides and mouldicides may also be used such as iodopropynylbutylcarbamate (IPBC), organic tin compounds such as tributyltin naphthenate, organic copper compounds such as copper 8 quinolinolate and copper naphthenate, organic zinc compounds, quaternary ammonium compounds, tertiary ammonium compounds, isothiazolones, triazoles such as tebuconazole, boron compounds such as trimethyl borate. Bethoguard is also particularly suitable. This would allow the formulation to be used as a permanent preservative as defined by Hazard classes 3,4 and 5 in Australian Standard AS 1604.1-2005 America Wood Preserves Association standards (USA) and MP 3640 (New Zealand).

In preferred embodiments, the active may be a metallic biocide. Metallic biocides are preferably copper or tin based compounds.

Preferred copper based actives include: alkaline (amine or ammonia) copper quats (ACQ), ammonium/copper, ammoniacal copper zinc arsenate (ACZA), bis(N- cyclohexyldiazeniumdioxy)copper, copper acetate, copper ammonium acetate complex, copper azole, copper borate, copper carbonate, copper citrate, copper/diethanolamine complex, copper/diethylamine complex, copper/ ethanolamine complex, copper/ethylene diamine complex, copper fluoride, copper fluoroborate, copper hydroxide, copper hydroxycarbonate, copper salt of 8-hydroxyquinoline, copper naphthenate, copper oxide, copper oxychloride, copper sulfate, copper/triethanolamine complex

In alternative preferred embodiments, the active is an organic biocide. Preferred organic biocides include IPBC, azoles, mixed azoles bethoguard.

Preferably, the active includes a combination of an organic biocide and a metallic biocide. Another highly preferred active is a combination of copper naphthenate and mixed azoles.

One highly preferred active is a combination of IPBC, Azoles and bethoguard. One particularly preferred composition is a combination of IPBC, Azoles and bethoguard in an 20:80 mixture of PBLO:heating oil. Drying agents such as cobalt, manganese, zirconium and copper naphthenate may be added to accelerate the drying of the drying oil.

In a second aspect, the invention provides a method of treating wood including treating wood with a composition according to the first aspect. Preferably, the composition is allowed to fully penetrate the wood. Preferably, the wood is treated with a composition of the first aspect in an amount of between 20 and 60 litres of composition per cubic meter of wood.

Preferably, the wood is treated with a composition of the first aspect in an amount of about 40 litres of composition per cubic meter of wood.

In a third aspect, the invention provides treated wood, wherein the wood is impregnated throughout with a composition of the first aspect. The composition is present in an amount of between 20 and 60 litres per cubic meter of wood.

The wood may be natural timber, or a composite product such as medium density fibreboard, plywood, laminated veneer lumber, medium density fibre board, particleboard, oriented strand board, agglomerated structural board, and structural members such as logs, poles posts, beams, sheets, mouldings. The treatment step can be conducted using conventional pressure application techniques such as existing vacuum pressure systems known in light organic solvent plants (LOSP).

Alternatively, the applicant has also found the mixture of the present invention can be applied without the need for pressure application. Treatment can be accomplished by spraying, dipping etc which, unlike previous conventional batch systems, is ideal for use on continuous production line facilities such as saw mills and production plants for engineered wood products.

A discussed earlier, the Australian standard requires that irrespective of the species of timber, i.e. natural durability class 1 to 4, the preservative shall penetrate all sapwood.

Brief Description of the drawings.

Figure 1 shows the effect of the ratio of extender to drying/semi drying oil on fungal activity. Figure 2 shows the effect of carrier and uptake on fungal activity.

Figure 3 shows the set up of a test procedure of the present invention.

Figure 4 shows representative results in an untreated sample.

Figure 5 shows representative results in a sample treated with a composition of the present invention .

Best method of performing the invention

Tests were conducted to verify the efficacy of the above mentioned compositions in preventing attach by various fungal organisms. Experimental treatments were carried out by dipping wood wafers (Sutter blocks)

(pinus radiata) in the candidate preservative system to give an uptake of approximately 401/m ³ . The wood wafers were then conditioned at ambient temperature for 14 days.

The wafers were then placed on agar plates with the candidate fungi. The wood plus fungi were then incubated at 25 ⁰ C and 75% relative humidity for 6 weeks. Determination of performance of the candidate biocides was by weight loss. Acceptable performance was less than 3% weight loss.

Table 1 shows the results of a number of different treatments conducted in relation to two different fungal species, Antrodia xantha and Paxillus panuoides.

Table 1 Treatment in Relation to Antrodia xantha and Paxillus panuoides.

As can be seen, the application of kerosene and/or PBLO controls alone at these levels of uptake are not sufficient to prevent decay of the wood. Using only the components of the carrier system, a substantial mass loss due to fungal decay was observed. PBLO alone may have some minor effect, however PBLO alone did not lead to acceptable minimization of fungal loss.

Diesel in conjunction with high levels of IPBC provided moderate protection against Antrodia Xantha, but not paxillus panuoides.

PBLO in conjunction with IPBC provided some reduction in mass loss against Antrodia Xantha, but again paxillus panuoides was still highly damaging. Using around 20% PBLO:80 Diesel in conjunction with an appropriate concentration of the biocide dramatically increased the efficacy against both types of fungus. Increasing the amount of PBLO to 40, 60 and even 80%, while still acceptable in some cases showed some diminution in the effect against fungal decay.

Acceptable results were also seen in carrier systems in the range of 10% PBLO to 40% PBLO. However, the best results were seen at around 20% PBLO.

Figure 1 shows the results presented in a graphical format. It can clearly be seen that 80:20 Diesel PBLO outperformed solvent mixtures with either 100% diesel or with lower levels of diesel, for both fungi tested. Using 80:20 diesel:PBLO led to a level of loss around half that of the next best carrier tested, neat diesel. Clearly, where the drying oil is present in around 10-30%, more preferably 10-20% and even more preferably around 10-15% of the carrier (eg 80:20 diesel :PBLO) there appears to be a synergy which allows the biocide (eg 0.03%IPBC) to be more effective than in either extender or drying oil alone.

Further, in the range of 10 to 40% PBLO, including at the preferred PBLO level of 20%, the impregnated timber still had good improved dimensional stability, water repellency and improved surface coating capability (paint adhesion), as well as improved handling properties, such as reduced splitting when nailing.

Surprisingly, and without wishing to be bound by theory, it appears as if the linseed oil in certain concentrations suppresses the activity of the organic biocides. This maybe due to some complexation with the biocide or caused by coating of the cell wall in such a way that the biocide is unavailable to them. Concentrations of PBLO in the 10-

40% range appear to provide optimal balance between timber penetration and potential deactivation of the biocide.

Optimal uptake was at around 4OL per cubic meter of wood. Increasing or decreasing uptake outside the range of about 20-60L per cubic meter led to decreased efficacy. For example, loading the formulations of the present invention onto wood at IOOL per cubic meter led to decreases in the efficacy of the formulation over the values at 4OL, even though two and a half times more biocide was being used.

A number of formulations were tested against a variety of fungi.

Table 2 shows the effect of ratios of high flash solvent (kerosene) and pale boiled linseed oil (PBLO).

Table 2 Treatment in Relation to F.lilacino and P. placenta

* Mean of 6 replicates per treatment

In this experiment, a copper based biocide and tebuconazole in the ratio of 25:1, as disclosed in WO 93/02557, were used as the biocides.

Two effects are observed, firstly with decreasing ratios of pale boiled linseed oil to high flash solvent the performance of the copper and tebuconazole improves (in relation to weight loss). Secondly with increasing concentrations of copper and tebuconazole weight loss decreases. In all cases the samples with copper and tebuconazole show less weight loss than the controls without copper and tebuconazole.

Table 3 shows the same combinations exposed to 3 other fungal species, C. olivacea, G. abietinum, and P. tephropor.

Table 3 Treatment in Relation to C. olivacea, G. abietinum, and P. tephropora

* Mean of 6 replicates per treatment

The data in Table 3 shows that these three species are readily controlled even at the lowest levels of biocides used. There is significant difference between the untreated controls and those formulations that include biocides i.e. as soon as biocides are present the fungi is controlled. The ratio of PBLO to high flash solvent also appears to have little effect.

Formulations including tebuconazole and propiconazole, were also tested against the 5 fungi previously tested. Table 4 shows the data collected.

Table 4 Treatment in Relation to F.lilacino C. olivacea, G. abietinum, P. tephropora and P. placenta

* Mean of 6 replicates per treatment

While overall the performance of tebuconazole and propiconazole in a mixture of kerosene and pale boiled linseed oil (70:30) was not as good as the same combination in white spirits, a dramatic improvement over the controls that did not contain tebuconazole and propiconazole was observed.

Table 5 shows the effect of high uptake of mixtures of kerosene and pale boiled linseed oil.

Table 5 Treatment in Relation to F.lilacino C. olivacea, G. abietinum, P. tephropora and P. placenta effect of high uptake (1/m ³ )

* Mean of 6 replicates per treatment

In this trial a 50:50 ratio of kerosene to PBLO was used and the uptakes ranged from 454 to 467 1/m ³ . In all cases there were 6 replicates. The high uptakes masked the performance of the biocides tebuconazole and propiconazole resulting in reduced dose response.

Figure 2 shows the effect of the carrier on the 5 fungi involved in the study. Only the 70:30 ratio of kerosene and pale boiled linseed oil treated at the very high uptake of 400 1/m ³ showed any effect on the fungi. All other carriers had similar weight loss due to fungal activity comparable with untreated timber, indicating that at the level of treatment preferred, the carrier system was not a significant contributor to wood protection. Carrier systems of the present invention, such as for example, the 70:30 ratio of kerosene and pale boiled linseed oil, maybe efficacious alone in preventing fungal decay if used at sufficient impregnation rates. Additional long term studies of decay resistance were carried out by Ensis Wood

Processing in Rotorua, New Zealand using radiata pine framing samples. A number of sets of radiata pine framing samples, treated with three LOSP/water repellent formulations had pre-inoculated decay feeder blocks attached to the ends and were placed in filleted stacks. The stacks were wrapped in polythene and kept in a chamber where there was a constant temperature of 25-27°C and relative humidity of about 90%. Preservative chemicals and water repellent additives were made up to a number of light organic solvent preservative (LOSP) working solutions. Ten samples of 90 x 45mm radiata pine framing were treated with each of the following solutions and a further ten untreated samples were used as an untreated control group. Treatment details are summarised below in Table 6.

Framecoat Blue is white spirit containing pale boiled linseed oil at the stated levels. Tanalith T is a high flash solvent, such as heating or diesel oil, plus PBLO at the stated levels, and was applied as an envelope to a depth of approximately 5mm. Framecoat F contained copper naphthenate as the biocide. Framecoat green contained an azole biocide.

TABLE 6 Solutions used to treat radiatia pine samples for long term studies

The stacks were uncovered after twelve weeks and the samples were removed, weighed and assessed for the spread of mycelium from the feeder blocks as follows:

Mycelium Spread Ratings

1 = No mycelium development onto the sample surface.

2 = Mycelium from the feeder block on the surface, spread less than 5mm.

3 = Mycelium from the feeder block on the surface, spread 5 - 50mm.

4 = Active mycelium from the feeder block on the surface, spread >50mm.

5 = Extensive mycelium over most of the sample width, <50% of the surface area. 6 = Extensive mycelium development over >50% of the surface area.

The surfaces of each sample were tested with a blunt probe to determine whether the decay fungi were damaging the framing. Staples were removed from one side of the sample so that the end joints could be opened and the internal joint area could also be assessed for decay. The decay rating system used was similar to ASTM D 1758, as follows:

Decay Ratings

10 = No decay or insect damage. T = Trace, discolouration or softening, not positively identified as decay. 9 = First stages of decay or damage up to 3% of cross-section. 8 = Lightly established decay, 3-10% of cross-section. 7 = Well established decay, 10-30% of cross section.

6 = Deep established decay, 30-50% of cross section. 4 = Severe decay, nearing failure, more than 50% of the cross section.

0 = Failed.

Samples were also assessed for mould development on the surfaces and given ratings according to the following scale: Mould Ratings

1 = No perceivable mould.

2 = Light mould or widely scattered spots.

3 = Extensive mould, numerous spots or widespread light mould.

4 = Severe mould, up to 50% coverage. 5 = Severe mould, >50% coverage.

After assessment the joints were stapled back together and the samples were placed back in their original position in the stack. The stacks were then re-wrapped in polythene.

ASSESSMENT RESULTS

Assessment results for the various treatment groups seen after twelve weeks are summarized in Table 7.

TABLE 7 Summary of Assessment Results - 12 Weeks

Overall the moisture content of the samples after twelve weeks generally reached levels within the 25-35% range. While differences in average moisture content between groups were up to 7%, there was no consistent pattern associated with preservatives or levels of PBLO.

The feeder blocks were positioned at the end of the main sample and touching the short end blocks. Mycelium from the feeder blocks had moved onto the surface of almost all treated samples. It had spread more than 5mm in many cases but seldom more than 50mm.

The fluffy white Auckland brown rot mycelium was often more prominent than the mycelium from Antrodia xantha and had spread slightly more than Antrodia xantha. Where mycelium was spreading on the surface it had usually penetrated the joint areas and was often accompanied by discolouration of the wood. There was little obvious difference between the preservatives. hi the untreated control samples the mycelium had frequently spread more than 50mm from the feeder blocks across fillets and sealed ends to treated samples.

After 12 weeks, all of the untreated control samples contained light-moderate decay at both ends, hi the groups treated with Framecoat Blue there was no decay or occasional early stages of decay in treatment groups 1 (0.48% IPBC + 9.4% PBLO), 2 (0.60% IPBC + 9.4% PBLO), 6 (0.40% IPBC + 18.8% PBLO) and 7 (0.40% IPBC control). There were seven samples with decay in group 3 (0.48% IPBC + 18.8% PBLO), four in group 5 (0.30% IPBC +18.8% PBLO) and three in group 4 (0.60% IPBC + 18.8% PBLO), although this was relatively minor in the group 4 samples. One sample in group 9 (0.24% IPBC + 9.4% PBLO), one in group 12 (0.24%

IPBC + 18.8% PBLO) and three in group 13 (0.30% IPBC + 18.8% PBLO) contained lightly established decay near the feeder blocks. Otherwise there was only occasional minor decay on samples treated with the low uptake, Tanalith T formulation.

The Framecoat green treated samples in group 14 (0.80% Azole + 9.4% PBLO) contained no decay but five samples in group 15 (0.80% Azole + 18.8% PBLO) contained decay.

The Framecoat F samples showed overall less resistance to decay due to the use of a copper resistant fungal strain. However, the degree of decay was still significantly below that seen in the untreated samples. For example, the joint decay score in untreated sample 27 was 7.4, compared to a joint decay score of 9.0 in the treated sample. In general, there appeared to be less decay in groups treated with a lower PBLO concentration. If groups of samples are compared where the only difference in the treatment solutions was either 9.4% PBLO or 18.8% PBLO, including the control treatments T16-T19, the number of samples with decay are 48 and 68 respectively. This suggests that higher concentrations of PBLO have, if anything, a detrimental effect on some of the preservatives as the concentration of PBLO increases.

Surprisingly, the use of less than 20% PBLO did not hinder the biocidal efficacy of the mixtures. For equivalent preservative retention groups, those with a higher concentration of PBLO frequently contained more decay.

The test pieces were then returned to their original positions and left for a further interval of time, whereupon they were re assessed after 26 weeks.

The moisture content of most samples was between 25% and 30%, and had declined by about 3% between the 12-week and 26-week assessments. Decay in some of the samples, particularly the untreated controls, reduced the sample weight and so may give a misleadingly low indication of moisture content. While the moisture content changes were relatively small the samples were quite dry on the surfaces. Feeder blocks had dried and distorted noticeably and patches of surface decay had shrunk and cracked indicating that conditions in the stacks were relatively dry. However the results are valid as all blocks were subjected to the same conditions.

Mycelium Development and Decay

There was little change in mycelium spread from the feeders compared to the 12- week assessment. While average mycelium spread ratings had increased slightly in all groups there had not been an obviously large increase on any samples, including the untreated control samples. Auckland brown rot mycelium was still more prominent than the mycelium from

Antrodia xantha, particularly at the end nearest the wall. On samples where there had

been extensive Auckland brown rot mycelium on the surface previously, much of this had degenerated into brown surface discolouration.

TABLE 8 Summary of Assessment Results - 26 Weeks

All of the untreated control samples contained moderate to severe decay at both ends. Decay in the treated samples increased slightly, more in the joints than on the

surface. This again was probably influenced by dry conditions in the stack. Of the untreated samples, only group 7, the IPBC treated control, was free from significant decay.

In the groups treated with Framecoat Blue, group 2 (0.60% IPBC + 9.4% PBLO) had the least decay. All other groups contained four or more samples with decay ratings of "8" or less i.e., more than 5% of the cross section. Groups with a higher IPBC retention had less decay. Conversely, equivalent IPBC treated groups had more decay where the 18.8% PBLO solution had been used. In the groups treated with Tanalith T (groups 8-13) decay ratings were very similar and there were 5-7 samples in each group with lightly established or established decay.

Differing levels of PBLO in the treatment solutions had little or no effect on decay. The Framecoat green treated samples in groups 14 and 15 were similar to the Tanalith T treated groups but with slightly less decay. The higher level of PBLO in the second treatment had not reduced decay. Treatment groups treated with Framecoat F continued to show less efficacy due to copper resistance of the fungus, but still exhibited an improved ability to ward off decay relative to untreated timber even in the case where the fungal species was resistant to the specific biocide used (untreated decay score was 4.7 after 26 weeks, while the copper treated timber had a decay score of 7.5). Decay, particularly surface decay, appears to have been slowed by dry conditions in the stack. However, it progressed slowly and more samples had decay ratings of "8" or worse than at the 12-week assessment.

If groups of samples are compared where the only difference in the treatment solutions was either 9.4% PBLO or 18.8% PBLO, including the control treatments 16- 19, the number of samples with decay are72 and 84 respectively. The corresponding average decay ratings are 8.9 and 8.6 respectively. This supports the trend seen after twelve weeks, which suggests that overly high concentrations of the PBLO additive are having either no effect or a negative influence on preservative efficacy. Surprisingly, the data suggests that less than 20% linseed oil does not hinder the efficacy of the biocides. Representative results can be seen in figures 4 and 5.

Figure 4 shows one untreated sample block from group 17 after 26 weeks exposure. Mycelium from the Antrodia xantha feeder block has spread well along the sample but the surface decay is only moderate. Decay in the joint area was more severe.

Figure 5 shows a sample treated with Tanalith T, 0.20% IPBC + 9.4% PBLO, 15 l/m3 after 26 weeks exposure. Mycelium from the Auckland brown rot feeder block had spread onto the surface of the sample and caused some discolouration but there was no surface decay and only very minor decay in the joint.