Proceedings e report - Firenze University Press

AGEING OF WOOD – DESCRIBED BY THE ANALYSES OF OLD BEAMS
Michael Grabner*, Maria Kotlinova
Institute for Wood Science and Technology, University of Natural Resources and Applied Life Sciences
Vienna, Austria
Abstract
Wood underlies ageing processes which means that the properties of old wood have been changed. Wood density
shows very close relationships to the amount of latewood (for softwoods only). There are no changes of the
wood anatomy due to ageing; except due to destruction by insects or fungi. Interior beams of two buildings
(felling of the trees 1720 AD and 1854 AD) were sampled. To understand the effect of ageing on wood density,
x-ray densitometric analyses of 10 beams from pith to bark were done. Plotting radial profiles of percentage of
latewood and wood density sometimes showed an increasing divergence of these trends with increasing cambial
age.
1. Introduction
Many buildings are preserved as important cultural heritage. A lot of theses buildings are unique
architectural and artistic objects [1]. Usually a lot of wooden structures can be found within these
buildings.
Wood remains durable when it is protected from weathering and biological attacks (insects and fungi)
but still underlies ageing processes. That means that the properties of old wood are altered [2, 3, 4].
Obataya [2] reported that wood loses strength, but stiffer with increasing time. Schniewind [7] found
evidence, that wood density of used, old wood can be lower as well as higher compared to recent
material. Wood quality, i.e. wood density, varies strongly – within the cell wall, within tree-rings,
within trees and across sites [5]. Wood density should always be compared with respect to the cambial
age (that is the number of tree-rings outside the pith) of the sample [6]. Typically wood density of
softwoods (as well as mechanical strength) increases with increasing cambial age (number of rings).
This is due to juvenile wood effects and due to age-related trends in wood formation [8]. Fig. 1 shows
the general trends of ring-width, latewood percentage and wood density with increasing tree-age.
Ring-width
Ring-width Ring-width
Latewood Latewood percentage percentage
Wood Wood density density
Increasing tree-age
Fig. 1: General trends of ring-width, latewood percentage and wood density
with increasing tree-age (for softwood only).
* E-mail: michael.grabner@boku.ac.at
Joseph Gril (edited by), Wood Science for Conservation of Cultural Heritage –Braga 2008: Proceedings of the International
Conference held by COST Action IE0601 (Braga - Portugal, 5-7 November 2008, ISBN 978-88-6453-157-1 (print)
ISBN 978-88-6453-165-6 (online) © 2010 Firenze University Press
Latewood percentage, wood wood density