Use of Confocal Profilometry to Quantify the Weathering of Wood

IRG/WP 09-20421

Chunling Liu, P Evans

The methods that have been used to screen chemicals for their ability to prevent the weathering of wood involve assessing the loss in weight and tensile strength of treated wood veneers or measuring the rate of erosion of exposed and unexposed (masked) wood subjected to weathering. The erosion of wood during natural weathering occurs slowly and long exposure times are required to produce differences in erosion of masked and unmasked areas that can be quantified using optical microscopy. The erosion of wood can be accelerated using artificial accelerated weathering and by selecting low density wood species that erode quickly, but specimens still need to be exposed to accelerated weathering for 600 hours before reproducible differences in the erosion of masked and unmasked areas can be detected using optical microscopy. Accurate measurements of the erosion of materials can be made using confocal profilometry. We hypothesized that the use of confocal profilometry would make it possible to more accurately measure the erosion of wood during accelerated weathering and hence shorten the exposure time required to produce reproducible differences in the erosion of masked and unmasked wood in samples subjected to accelerated weathering. In this study we tested this hypothesis by using confocal profilometry to assess the erosion of western red cedar wood exposed to artificial accelerated weathering in xenon-arc and QUV weatherometers for 100, 250, 500 and 1000 hours. We also assessed whether erosion was affected by the size of the unmasked area exposed to artificial accelerated weathering. The erosion of wood specimens during artificial accelerated weathering increased with time as expected. Specimens exposed in the xenon arc weatherometer eroded significantly faster than specimens exposed in the QUV weatherometer. There was a positive correlation between the size of the unmasked area and the erosion of wood during artificial accelerated weathering. Our results confirm that confocal profilometry can accurately measure the erosion that occurs when western red cedar wood is exposed to only 100 (xenon arc) or 250 (QUV) hours of artificial accelerated weathering. We conclude that confocal profilometry is a faster, more accurate and less labour-intensive way of measuring the erosion of wood during accelerated weathering than optical microscopy. The implications of our findings for the development of surface treatments and preservatives that can maintain the appearance of wood exposed outdoors are briefly discussed.


Keywords: confocal profilometry, artificial weathering, erosion measurement

Conference: 09-05-24/28 Beijing, China


Download document (63 kb)
free for the members of IRG. Available if purchased.

Purchase this document