In situ, in vitro and in silico analysis of coating performance

Service life prediction (SLP) is a complex yet essential method for analysing coating performance. Accurate and precise assessment is crucial for a strong position on the market. Correct knowledge of the critical failure points, maintenance/replacement frequency and related costs are part of this approach. This paper describes the scale-dependent tools within a bio-engineering framework that are applied for coating research, ranging from modelling, X-ray tomography, lab testing, controlled fungal infestation up to continuous moisture set-ups and large-scale window frame weathering

Moisture conditions in coated wood panels during 18 months natural weathering at five sites in Europe

Wood moisture content of coated panels of Scots pine sapwood was recorded during 18 months natural weathering in Vienna by logging electric resistance and temperature near the surface. Eight coating systems with various film thicknesses were used, including three solvent borne alkyd stains, three water borne acrylic stains and two water borne acrylic paints. At five sites in Europe wood moisture content of panels coated with three solvent borne alkyd stains, a brow acrylic stain and a white opaque acrylic paint was recorded weekly by changes in panel mass. Fluctuations in wood moisture content were influenced by the film thickness, moisture protection and colour of the coating systems used. Degradation phenomena led to decreasing moisture protection of less durable coating systems over time of exposure. Differences between the exposure sites were relatively low, except the site in the UK where moisture conditions were higher

Preventive action of organosilicon treatments against disfigurement of wood under laboratory and outdoor conditions

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Investigating plywood behaviour in outdoor conditions

Moisture behaviour of plywood is investigated in combination with detailed structural analysis. In the lab, neutron radiography and X-ray computed tomography (X-ray CT) were used to map the moisture distribution and internal structure of plywood respectively. In an outdoor natural weathering test, the average moisture content (MC) and moisture distribution of plywood were monitored using a continuous moisture measurement set-up and an adapted electrical method, respectively. The structural changes of the specimens during weathering were recorded by using X-ray CT. Based on the interrelationship of moisture behaviour and structure, suggestions are given for improving the water resistance of plywood by optimising structure

Non-destructive evaluation of wood decay

Evaluation of wood decay is often prone to subjective assessment. Standard rating scales are based on human perception of decay, often in addition to weight loss measurements. Especially the assessment of graveyard specimens or other long term testing material that has to be monitored regularly on a non-destructive basis, is challenging. In this paper two techniques are presented that can deliver extra insight. The first technique is based on the analysis of the resonance frequencies of the material. It is very fast and only minimal sample manipulation is required. Instantaneously, an approximation of the modulus of elasticity (MOE) and damping are obtained that can be followed during degradation. The technique is applicable in the field. The second method requires an X-ray tomography scanner, but enables a three dimensional view on the internal structure of the sample and accompanying degradation. It is not applicable in the field but can give a very interesting view on possible degradation patterns. Both methods can not only assist in non-destructive assessment, but can possibly best serve as early decay detection techniques and give more insight into the rate and modes of degradation

Outdoor weathering performance parameters of exterior wood coating systems on tropical hardwood substrates

Wood coating research almost exclusively focuses on softwood as substrate despite the fact that coatings applied on tropical hardwoods show a different weathering behaviour. The objective of this study was to quantify the impact of wood substrate and coating type on the weathering behaviour of finished wooden joinery in outdoor exposure using a set of statistical methods. Therefore, a broad range of white opaque paints and mid-oak semi-transparent stains were used. The coatings were industrially applied on window frames made of frequently used commercial tropical hardwood species. The general appearance of the wood/coating systems was assessed visually using a rating scale that takes into account the anatomical characteristics of hardwood. For the evaluation, a required minimum exposure time of 2.5 years outdoor weathering for joinery in vertical position and facing south-west was determined. At 30 months best performances were recorded for waterborne alkyd primers with an acrylic topcoat when dry coating film was sufficiently thick. The dry layer thickness also affected the impact of the hiding power on the performance of the wood/coating system. Within hardwood species the degradation rate of coatings on species with a fine texture was the lowest. The significant influence of the substrate's texture on the weathering behaviour of coated hardwood stressed the need to evaluate the wood/coating system in total

Moisture behavior and structural changes of plywood during outdoor exposure

Plywood is an important wood-based construction material yet prone to water uptake, as such potentially decreasing mechanical properties and increasing decay risk. It is, therefore, essential to understand the moisture behavior and structural changes of plywood in service. In this research, several plywood specimens were exposed in outdoor weathering conditions for approximately one year. During this period, the average moisture variation of and moisture distribution in different veneer layers of a set of plywood specimens and detailed field weather information were recorded continuously. The internal structure of the specimens was also monitored by periodically scanning using X-ray CT. Measurements indicate that moisture distribution in plywood is not homogeneous in outdoor conditions. The second layer can, in some plywood types, accumulate a significant amount of rain, and long rainy periods and cloudy weather can keep the moisture content of the inner layers of plywood significantly high. Moisture accumulation and moisture dynamics, in combination with wood species, are the main factors causing structural changes, mainly occurring as cracks, of the plywood veneers in service. The glue line between the veneers, however, is not ruptured after one year of outdoor exposure. Plywood with layers having a slow water sorption and fast water desorption could effectively avoid internal moisture accumulation and cracks in service. Based on the knowledge of the interrelationship of weather data, internal moisture behavior and structural changes in service, fit-for-purpose design of plywood could be improved and service life prediction is at hand