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Finishes for outdoor timbers
1975 - IRG/WP 378

Protecting wooden structures
1980 - IRG/WP 392
Chromium-containing chemicals that effectively retard weathering of wood improve performance of subsequently applied finishes. Current work is focusing on the performance of wood-derived products (plywood, hardboard, fiberboard, particle board) after surface treatment with inorganic chemicals. The overall objective of the continuing research is to investigate new environmentally safe procedures to stabilize wood surfaces and to improve performance of applied finishes.
W C Feist

Exterior wood stains
1980 - IRG/WP 3135
Experience has shown that conventional paints cannot now be relied upon to provide a complete seal against water entry, that in practice water can often circumvent the film and that the paint, far from serving to keep water out will seal it in. Moreover present-day paints are often subject to localised and premature failure out of doors and consequently entail high maintenance costs. Problems of wood decay and premature paint failure reached a high level during the 1960s, and led to the acceptance of the need for the preservative treatment of softwood joinery and cladding. The question remains however, whether, in the light of changes in the quality of timber and how it is used, the traditional approach of attempting to seal the outer surface of the wood is still valid, or should be abandoned in favour of using different types of finish which are more permeable to moisture and prevent it accumulating in the timber. One of the reasons for the remarkable success of semi-transparent exterior wood stains is that they met the demand for finishes of increased water vapour permeability for timber which was susceptible to decay. They also possessed two other important attractions: they provided natural finishes for exterior timber which were without the technical problems of clear varnish; and their mode of breakdown by erosion reduced the preparation work in maintenance and hence the overall maintenance costs. These are valid commendations for stains and remain important factors encouraging their use. Stains offer the architect additional design freedom and, used effectively, can make a pleasing contribution to the appearance of modern buildings. They do reduce average moisture levels in the timber and are simple to maintain, though these advantages may be offset to some extent if more frequent maintenance is necessary and if the higher permeability creates problems from dimensional movement.
E R Miller

Durability of exterior natural wood finishes in Brazil
1985 - IRG/WP 3343
Wood finishes systems were evaluated in natural weathering conditions during 5 (five) years, over "Parana-pine" (Araucaria angustifolia). Test samples results show that: - Semitransparent wood preservative stains, based on polimerized linseed oil, provided very good protection to the wood, compared with the one based on alkyd varnish; - Solid color wood preservative stains provided good durability. However, film degrading process was identical to the one of conventional finishes; - Conventional paint and varnish showed decomposition caused by cracking, checking and flaking (scaling).
D R Macedo

Weathering trials on natural wood finishes in New Zealand
1986 - IRG/WP 3383
The weathering properties of various transparent and semi-transparent exterior finishes for New Zealand-grown radiata pine are currently being examined. After 12 to 16 months' weathering, unpigmented water repellents have failed to provide satisfactory protection from weathering under field test conditions. With the exception of two formulations, penetrating oil-based stains are already showing signs of deterioration by surface erosion. Non-penetrating solid colour stains have generally remained in good-to-excellent condition. Acrylic emulsion formulations are the most durable of the transparent finishes under test.
D V Plackett, C M Chittenden

Preservatives stains as exterior wood finishes
1977 - IRG/WP 389
For many years wood preservatives and paints have been used as the only treatment for exposed wood surfaces. Because of the inherent color of the preservatives, such as creosote, the wood surface was stained as well as protected from attack by micro-organisms. Paints protect surfaces from weathering, but recently, with an increased interest in maintaining the more natural appearance of exterior wood surfaces, painting is being replaced by staining. Stains have the advantages, in addition to preserving the natural wood appearance, that they do not peel, blister or crack, can be applied easily and renewed with little difficulty. The cost is less than that of paint, initially and over the life of the building. One of the major attractions for homes is that stains blend in with the environment. If the home owner desires a white exterior or bright colors, paint rather than a preservative stain must be used. Paints are more effective in protecting the wood from damage by sunlight and will avoid discoloration of the exterior surface resulting from the natural extractives present in wood. Special aluminium or stainless steel nails are not needed with paints, but are needed with stains. Preservative stains can be classified in various ways. Wood preservatives, such as creosote and pentachlorophenol, have been used for many years primarily for preventing deterioration caused by fungi, including fungus species which discolor and those that decay the wood. These compounds provided some degree of water repellency, but this was not a major objective in their use. Later, water repellents were added to the preservatives to reduce the rapid uptake of moisture and thus provide some dimensional stability to the product. More recently water solutions of inorganic salts have demonstrated that they provide protection to the wood, add color and are beneficial primary treatments if the wood surface is to be painted. Some of the water soluble formulations may provide some fire retardant properties as well. A common system of classification today includes three general types of natural finishes as follows: 1. water-repellent preservatives; 2. pigmented penetrating stains; 3. inorganic water soluble salts. It is possible to obtain a satisfactory exterior surface if no treatment is applied. Such an approach, however, is satisfactory only where the weather is not favorable for micro-organisms. If the fungi and other micro-organisms are allowed to develop, the coloring will be very nonuniform, the wood surface will deteriorate, and warping and the like will occur to excessive degrees. Thus in most environments one of the above systems must be used.
D W French

Proposed method for out-of-ground contact trials of exterior joinery protection systems
1981 - IRG/WP 2157
Methods for testing the efficacy of preservative treatments for exterior joinery are described using the format of a European Standard. Commercially used treatments applied to jointed test units (L-joints) which are then protected by conventional finishes are exposed to normal outdoor hazards out of ground contact. Assessment is made a) by determining eventual failure through decay and b) by destructive examination of replicate treated and untreated units, after increasing time intervals, rating comparative performance in terms of wood permeability increase and the progress of microbial colonisation.
J K Carey, D F Purslow, J G Savory

Developments in the protection of wood and wood-based products
1980 - IRG/WP 340
Technology is playing an increasingly important role in the field of wood protection. This current review highlights how modern techniques have provided greater insight into the biological and physical processes affecting the durability of wood and wood-based products. Emphasis is also given to developments in preservative testing methodology and to the encouraging changes towards both the correct use of timber and the improvement of Standards and Codes of Practice. A final section, on recent technical developments in wood preservation, considers subjects ranging from an evaluation of new specific biocides to methods of increasing the permeability of refractory timber species.
J M Baker

Effect of protective additives on leachability and efficacy of borate treated wood
2002 - IRG/WP 02-30290
Borate preservatives have been used extensively in many countries as an effective means for protecting wood against fungal and insect attack especially in interior environments. Under exterior conditions, borate compounds have a main disadvantage as they can be leached from treated wood as a result of their water solubility. In this study, we compared the potential of different additives for reducing the leachability of boron preservatives from treated wood. Scots pine sapwood (Pinus sylvestris) and poplar (Populus trichocarpa x deltoides) test samples were vacuum treated with 1 % BAE (Boric Acid Equivalent) disodium octaborate tetrahydrate (DOT) solutions containing various additives e.g. glycerol/glyoxal, polyvinylpyrrolidone (PVPY), a commercial resin compound and a commercial water repellent. The European Standard EN 84 was used as a leaching test for both coated and uncoated specimens. The results of chemical analysis of leachates taken at different periods showed that the use of protective additives reduces the boron leachability. The glycerol/glyoxal additive applied to treated pine sapwood showed the best performance. The percent of boron retained in uncoated pine sapwood was 26% while coated samples still retained 45% after 14 days of intense leaching. Similar tests on poplar revealed 19% and 34% for uncoated and coated samples, respectively.This represents a gain of 20 to 25% compared to pure DOT treated specimens of both wood species. Preliminary biological tests were carried out on malt agar using a miniblock technique for uncoated pine sapwood and beech, with Poria placenta and Coriolus versicolor, respectively. After six weeks of exposure to fungal attack all boron protective systems tested proved their effectiveness, as none of the test samples exhibited a mass loss exceeding 4%. The reference 1% BAE without protective additives showed an average mass loss of 15%. Finally, test data are reported of standard EN 113 testing in view of a further evaluation of the biological efficacy of combined DOT-additive treatments.
A Mohareb, J Van Acker, M Stevens

Exterior weathering trials on radiata pine roofing shingles
1985 - IRG/WP 3240
A series of test roofs clad with radiata pine (Pinus radiata D. Don) shingles that had been pressure-treated with various water-borne preservative formulations were installed at a Forest Research Institute test site in Rotorua in 1977. A further series of test roofs installed in 1978 included radiata pine shingles pressure-treated with a commercial light organic solvent preservative (LOSP). Evaluation of selected radiata pine shingle test roofs in early 1984 showed that, although preservative leaching had occurred from shingles treated with an alkyl ammonium compound (AAC), a copper-chrome-arsenic (CCA) preservative, and an LOSP, the shingles appeared sound when examined microscopically. Slight lichen growth was evident on some shingles. In contrast, untreated radiata pine shingles displayed marked fungal infection, early stages of decay, and plentiful mould and lichen growth. Western red cedar (Thuja plicata D. Don) shingles, which were used as a reference point from which to judge radiata pine shingles, showed lichen and mould growth after seven years' exposure. Checking and cupping of western red cedar shingles were attributable in part to the inclusion of some flat-sawn material.
D V Plackett, C M Chittenden, A F Preston

The use of zirconium as an inert fixative for borates in preservation
2001 - IRG/WP 01-30256
Stand-alone borates have been used in internal protected situations as wood preservatives for about 60 years. They have not been deemed acceptable for external situations because of their leaching characteristics. Work carried out to reduce the leachability of borates has been reviewed briefly here, and a specific fixation agent based on zirconium has been tested in standard leaching and decay tests. It was found that the performance of zirconium could be optimized for fixation at specific drying temperatures and at higher formulation pH. Using sufficient quantities of ammoniacal zirconium carbonate and potassium zirconium carbonate such formulations are then able to pass both Standard European and American Wood-Preservers' Association methods designed for testing exterior wood preservatives. Formulations based on borate with a zirconium additive are probably suitable for use in exterior above ground and possibly ground contact situations. As only initial indicative tests have been carried out so far, further testing with a range of wood destroying organisms and field tests should be carried out to evaluate this system further.
J D Lloyd, J L Fogel, A Vizel

Laboratory experiments on aerial emissions from wood treated with wood stains
1993 - IRG/WP 93-50001-06
Due to the actual environmental interest in wood preservation, a series of experiments was carried out on the emission of biocides from treated wood. The research focussed on the volatilization of 5 biocides from boards treated with wood preservative finishes containing dichlofluanide (DCF) azaconazole (AZA), pentachlorphenol (PCP), iodopropynylbuthylcarbamate (IPCB) and tributhyltinoxide (TBTO). Formulations used were solventborne or waterborne and varried from low build to high build types. Treated samples were exposed in a standard emission column to a conditioned air stream and the emitted gasphase was adsorbed on amberlite xad. The chemical compounds were released in an appropriate solvent and subsequently analysed. A distinct variation was observed between the emission results of the different biocidal compounds. The volatilization values decreased in the following order: TBTO > DCF > IPBC > PCP >> AZA Relating the chemical concentration, obtained under various conditions of test to the inherent toxicity of the preservatives, it can be concluded that azaconazole possesses the lowest aerial toxicity potential. PCP and TBTO are considered to possess a lower aerial safety factor, while dichlofluanide and IPBC take an intermediate position. A significant effect of some of the exposure variables used could be noticed e.g. temperature, application dosis and exposure period. Other variables of importance were type of formulation, pre-curing of coating, moisture content and type of wood. As an overall conclusion, the emission tests gave evidence of no real danger for human inhalation toxicity. In none of the conditions used, for any preservative, the level of emission exceeded the maximal aerial concentration, cited in literature.
G M F Van Eetvelde, M Stevens

Preservative requirements for exterior particleboard as predicted from accelerated laboratory evaluations
1976 - IRG/WP 265
Arguments for and against preservative treatment of exterior particleboard were considered; it was concluded that preservative treatment is desirable. Laboratory decay tests were conducted to determine levels of sodium pentachlorophenoxide required to protect exterior particleboard from decay fungi. The decay resistance of treated board was compared with that of timber (both naturally durable and preservative-treated) currently used in situations for which exterior particleboard is designed. A retention of 0.35% sodium pentachlorophenoxide per oven-dry board weight was considered to offer adequate protection to the board.
M E Hedley

Blue stain resistance of exterior wood coatings as a function of their typology
1998 - IRG/WP 98-20145
Paints and wood stains were evaluated on their blue stain resistance using both EN 152 method and the reverse method. The typology of these exterior coatings was varied including standard and high solid solvent-borne coatings as well as different types of waterborne coatings. For the water-borne acrylic, alkyd based and hybrid coatings both applied as opaque primer paints and as decorative wood stains a range of synthetic resins were used. Though some components like dryers or bactericides are present in a number of formulations examined, a clear tendency of dependence of blue stain resistance on the typology of the coating seems obvious when evaluating blue stain development in an early stage. Longer exposures to test fungi fade away the effect of resin and indicate the role of a chemical protection of the coating.
J Van Acker, M Stevens, C Brauwers, V Rijckaert, E Mol

Natural durability of European wood species for exterior use above ground
2003 - IRG/WP 03-10499
The main interest in using more timber for exterior constructions is to protect the environment, where wood is considered an environmentally friendly material. However, chemicals for wood protection are getting more and more restricted, consequently, the focus on the natural durability of wood is increased. Good, well-documented data on the durability of wood species in ground contact exist, which form the basis of the standard EN 350-2:1995. Yet, we have, however, no useful documentation for the natural durability of wood, when used outdoors above ground. The study is large-scale field trials, including more than 30 species, where the objective is to define and document the natural durability of European wood species when used outdoors above ground. The idea of the test set-up is to simulate different application situations of wood to recommend individual wood species for specific purposes – fit to purpose. Two basically different test set-ups are used: 1. Panels in close-to-practice applications: Horizontally oriented with and without covering. Vertically north turning and vertically south turning oriented with and without covering as well as 45 degrees south turning oriented without covering. 2. Lap-joints in standardised field exposures: The set-up is according to the CEN-standard ENV 12037: Wood Preservative – Field Test Method for determining the relative protective effectiveness of a wood preservative exposed out of ground contact – Horizontal lap-joint method. The paper presents the results of the appearance, the moisture fluctuation, mould growth and wood decay after 3 years field trial.
B Lindegaard, N Morsing

Xenon simulation of natural weathering of external joinery preserving - Finishing systems
1992 - IRG/WP 92-2412
Semitransparent wood stains ('lazures') for external joinery have developed by means of product combination towards complete wood finishing systems that are easy to applicate, have a good weathering resistance and low maintenance cost. The search for enhanced formulations and the possibilities to standardize these products or treatment systems are always facing long periods of weathering tests. Extensive research was conducted to compare natural weathering with artificial ageing, using a scheme based on two cycle units commonly used for artificial weathering and intermediate low temperature exposures. Statistical analysis of test results showed good similarity between both natural weathering and Xenon ageing
J Van Acker, M Stevens, M Nys

Blue Stain Testing of Alkyd and Acrylic Stains
2003 - IRG/WP 03-20273
Resistance against blue stain of semi-transparent alkyd and acrylic stains was tested by both EN 152 and the so-called reverse exposure test methods. Comparison of the results, obtained by both methods was the most important aim of this study. As expected, performance of the water-borne acrylic paint was lower compared to protective effectiveness of the alkyd stain. This difference was even more pronounced when artificially accelerated aged samples were exposed. It seems that the reverse exposure method may give more distinctive results. In general, our results confirm previous literature reports on adequacy of the reverse test method for evaluation of blue stain resistance of surface finishes.
M Petric, M Pavlic, B Kricej, M Humar, F Pohleven

Evaluation of chlorpyrifos and fungicides alone and in combination for control of insects and fungi in wood and wood composites
1998 - IRG/WP 98-30187
Wood composites are rapidly being adapted for use in exterior applications. The incorporation of a preservative system to prevent fungus and insect attack is necessary with most exterior composites. Research studies were reviewed pertaining to organic preservative systems based on Lentrek* insecticide wood treatment which contains the active ingredient chlorpyrifos alone and in combination with tebuconazole and propiconazole (fungicides) for use as a combination treatment preservative system for solid wood and wood composites. Effective retentions for chlorpyrifos for protection of wood from termite and beetle attack was determined to be 0.2 kg/m3 set by the high retentions needed for field control of Coptotermes formosanus. In addition, this retention also provides effective control of the termites; Coptotermes lacteus, Reticulitermes flavipes, and Nasutitermes exitiosus, and the Lyctiid powderpost beetle, Lyctus brunneus. Retentions needed for control of Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) were determined to be 0.11 kg/m3 and 0.06 kg/m3 for tebuconazole and propiconazole, respectively. Discussions with the manufacturers of tebuconazole and propiconazole indicated that the two fungicides work best together when in a 1:1 ratio. Given the need for the 1:1 ratio then, retentions needed for the tebuconazole and the propiconazole for treatment of wood composites are therefore 0.1 and 0.1 kg/m3, respectively, using tebuconazole as the benchmark. Tebuconazole and propiconazole retentions of 0.08 and 0.08 kg/m3, respectively, afforded moderate stain and mold protection of treated wood with a 64% reduction in stain and mold coverage by 3 weeks; thereafter, protection diminishes with time to a 40% reduction in coverage by 8 weeks. Overall, the retentions needed for a mixture of tebuconazole/propiconazole/chlorpyrifos (T/P/C) for use in wood composites are 0.1/0.1/0.2 kg/m3, respectively, to protect the wood from attack by insects and decay fungi while at the same time providing some moderate reduction of stain/mold coverage. Also, in order to compensate for the anticipated long term degradation of the two fungicides under field conditions, the fungicide retentions were increased by 50% thereby resulting in final recommended retentions for use of T/P/C in wood composites as 0.15/0.15/0.2 kg/m3, respectively.
M P Tolley, P E Laks, R Fears

Performance of different treatments and finishes on wood out of ground contact. Preliminary results
1984 - IRG/WP 2221
Pinus and Eucalyptus L-joints treated with CCA, a water dispersable PCP and untreated ones were painted according to seven different finish's schedules and exposed at two sites in State of Sao Paulo. After ten months of exposure, it was possible to verify that preservative treatment improve the performance of both wood and finish. It was also possible to observe that wood substrate, preservative treatment, kind of finish and site of exposure had a great influence on finishes' surface colonization by both algae and mould fungi.
S Milano

Comparative study of blue stain resistance of various types of wood stains after artificial and natural weathering
1992 - IRG/WP 92-2411
For the determination of the protective effectiveness of a preservative treatment against blue stain in service, artificial weathering has been proposed as an alternative for the natural weathering period of 6 months in the European standard EN 152. Research on a range of products and on complete finishing systems for external joinery was conducted during 1986-1990. It revealed that the decisions drawn after 4 weeks Xenontest do not always confirm those of the EN 152 natural weathering test. Results were influenced by the nature of the formulation, the resin binder and the product combination (treatment system). However the variation among the ageing methods generally does not effect the practical conclusions on the blue stain resistance when well-defined limits are considered.
J Van Acker, M Stevens, M Nys

Exterior wood stains
1979 - IRG/WP 3136
The use of semi-transparent exterior wood stains has grown remarkably since their development during the 1960s. This can be partly attributed to their offering a break with tradition at a time when it was being recognised that changes in the quality of timber and how it was used demanded different methods of exterior wood finishing. Information is already available on the characteristics and uses of exterior wood stains. This paper presents the current opinion on their performance and limitations, based on continuing research and considerable site experience. Until now there has been greater use of the so-called lowbuild stains which deposit little film onto the timber and so come closest to the ideal natural finish. They have a high moisture permeability, which has the benefit of reducing the level of any decay hazard but can lead to wide fluctuations in moisture content in service and to consequent problems of surface splitting and dimensional movement. In order to limit movement it is necessary to maintain the water repellency of the stain by periodic retreatment which, on exposed aspects, is likely to be necessary at intervals of about three years. High-build stains form a surface film about half the thickness of a conventional paint film and they possess a moisture permeability between that of paint and typical lowbuild stains. They exert more control on wood moisture content, reducing the problems of dimensional movement and surface splitting, and should not require such frequent maintenance as the low-build types. However, high-build stains are more prone to localised failure by flaking and this tendency will increase after a number of maintenance coats, which will also tend to obscure the natural features of the wood. Thus it is possible that the improved protection provided by high-build stains may be offset by losses in appearance and ease of maintenance, but there is at present insufficient experience of them in Britain to establish the extent to which this is so. Some high-build stains are based on water-borne acrylic agglutinants and have very good durability although when used as the sole treatment they lack the freshness of the solvent-borne materials and the thermoplastic nature of the film creates problems on contacting surfaces. Interest continues to grow in the opaque stains, or moisture-regulating paints. These materials share with stains the characteristics of being applied coat on coat instead of by the normal primer/undercoat/finish procedure, and of weathering by erosion. They have the appearance of satin finish paint but should possess improved flexibility and higher moisture permeability, and be easier to maintain. There has also been a revival in interest in the Swedish Royal Process which effectively combines wood preservation and decoration. The timber is vacuum-pressure impregnated with a water-borne preservative and is then subjected to a pressure treatment with a heated mixture of oil and pigments to confer colour and weather resistance to an outer zone of the wood. Experience suggests that the maintenance requirements of Royal-treated wood are much reduced.
E R Miller

Minimisation of the Environmental Impacts of Coatings on Exterior Wood by Optimisation of their Life Spans
2003 - IRG/WP 03-50197
The study has shown that the environmental impacts from coatings on exterior wood are dependent criteria on their life spans. A minimisation of the environmental impacts can be performed with the help of the integrated design model, which is tested in this study. The optimal life spans, found as reference service lives from the exposure tests, statistical evaluation and the assessment of experts were used for forecasting in Life Cycle Assessment of the coatings on exterior wood. The integrated life cycle design, performed in this study, showed that the water-borne acrylic coating and the water-borne acrylic stain are the best choice as regards the integrated assessment of the environmental impacts and service lives of the coatings. The discussed coating systems are a solvent-borne alkyd coating, a water-borne acrylic coating, a water-borne acrylic stain, a solvent-borne alkyd stain and an alkyd oil.
L Strömberg

L-joint based testing for service life prediction of exterior plywood in out of ground contact conditions
2006 - IRG/WP 06-20342
Good biological performance of several plywood types in exterior conditions is most probably related to altered wood moisture behaviour compared to solid wood. Therefore a test set up was developed, using EN 330 L-joint testing methodology, to facilitate differentiation of plywood for exterior applications. The proposed test set up is an adaptation of an accelerated L-joint method introduced by Van Acker and Stevens (2003). Regular L-joints are used to expose plywood specimens as an infill window system. The L-joints simulate bottom corners of a low quality joinery unit. Accelerated testing is based on a moistening device using a drip irrigation system feeding a horticultural rock wool sponge as wetting agent. This keeps the lower corner of the plywood sample wet and creates a moisture gradient in the panel. The specimens are inclined for 10 degrees, the face veneer of the plywood is facing south and inclined 45°. The newly developed exposure method is intended to be severe and acts as a simulation of a worst case situation. The accelerated weathering makes differentiation among several plywood products possible after only one year of outdoor exposure. Visual appreciation of the tested plywood, mass loss measurements, alterations in moisture absorption and desorption patterns and isolations of fungi present on the samples help to rank plywood in view of fit for purpose for use class 3 exposure conditions.
J De Smet, I De Windt, J Van Acker

Decay Hazard Classifications in China for Exterior Above-Ground Wood
2007 - IRG/WP 07-20357
A decay hazard map for exterior above-ground wood structures is presented based on Scheffer’s Climate Index, with the major purpose of promoting awareness for proper protection of wood structures in different locations in China. A very large area in the South, including southern Yunnan, most of Sichuan Province and Chongqing, and part of Hunan, Hubei, Anhui, Jiangxi, and Zhejiang, as well as all the more southern areas, has decay hazard ratings above 70, considered a severe decay hazard zone according to the accepted classifications. The moderate decay hazard zone, Index values between 35 and 70, consists mainly of the central areas of China, from the west to the east, including parts of Xizang, Yunnan, Qinghai, Gansu, Shaanxi, Shanxi, Henan, Hubei, Anhui and Jiangsu, as well as Shanghai. It also includes most areas in Northeast China, together with a small pocket around Beijing. By comparison, large areas in the north, from the west to the east, including most areas in Xinjiang, Inner Mongolia, part of Qinghai, Gansu, Ninxia, Shaanxi, Shanxi, and Hebei, and a small part of Henan, are in a low hazard zone with index ratings below 35. The research demonstrates that the areas across China in the Southwest, South, Central China, Southeast, and Northeast, with the highest population densities and also containing areas on the east coast with the strongest economic development, have severe to moderate decay hazard for above-ground wood structures, making proper wood protection more critical and economically important.
J Wang, X Wu, M Jiang, P I Morris

Improving the Dimensional Stability and Fire Resistance of OSB by Roller-Coating Panels with UV-Curable Finishes
2008 - IRG/WP 08-40434
Oriented strandboard was sanded and roller-coated with UV-cured finishes. The effects of these treatments on the surface roughness, dimensional stability and fire resistance of OSB were assessed. Sanding reduced the average roughness of OSB, but it had a smaller effect on maximum roughness because sanded boards still contained surface voids between some strands. Sanded boards absorbed less than half of the coating material of unsanded boards, and when they were finished with a UV-cured coating system consisting of filler, sealer and two top-coats they absorbed less water and were almost as dimensionally stable as unsanded and coated boards. The swelling of coated boards after 72 h immersion in water was less than one third of that of uncoated OSB. This reduction in swelling compares favourably with that which can be achieved using chemical or thermal modification of OSB. Coated boards were more fire resistant than uncoated ones, but sanding reduced the fire resistance of OSB (coated and uncoated), possibly because it removed part of the densified surface layer from panels. Hence, we conclude that light surface sanding makes it easier and more economical to apply moisture resistant finishes to OSB using roller coating, but it should not be used prior to application of fire-retardant finishes.
P D Evans, I Cullis

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