Thesis (MScFor (Forest and Wood Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Balau, a group consisting of 21 Shorea species, is widely used for outdoor application. In
South Africa, Balau is one of the most popular materials used for decking. Due to the
increasing scarcity of Balau, it is of economic importance to investigate the possibility of a
substitute timber for decking material. One possible timber could be Colorado, a mixture
containing one or more of the following: Eucalyptus camaldulensis, Eucalyptus tereticornis
and their hybrids. These two species and their hybrids are extensively cultivated in countries
such as Australia, India and parts of South America because of their short rotation period and
easy adaptability to a wide variety of soil and climatic factors. The timber was initially
utilized as raw material for the pulp and paper industry but is now gaining importance in
structural uses like furniture, flooring and decking.
The aim of this exploratory study was to investigate relevant material properties and to
examine the natural and accelerated weathering behaviour of Colorado and Balau to predict
Colorado’s suitability as decking material.
It was found that Colorado had smaller vessel lumina, fewer vessels/m2 and smaller rays than
Balau and had a higher density than Balau. Although both timbers had a relatively low FSP,
Colorado’s FSP was 2.3 percentage points higher than Balau’s. The swelling coefficients
(radial and tangential) of Colorado were slightly higher than Balau’s but Colorado’s lower
swelling anisotropy can result in a lower tendency to twist in service. Colorado had a higher
water soluble extractive content than Balau, which can lead to the rapid initial colour changes
when the timber is exposed uncoated.
The weathering performance of Colorado and Balau was investigated by exposing samples in
a QUV accelerated weathering apparatus and to natural weathering at an inland and a marine
location. During weathering Colorado showed a slightly higher colour change ( E*) than
Balau. Balau showed a higher increase in roughness (Rz), surface checking and check
formation than Colorado. Colorado showed slightly more cup than Balau, however, Balau
showed much larger amounts of twisting than Colorado. No statistically significant
differences were found between the hydrophobicity of the two timbers. A coating was
effective in increasing the initial hydrophobicity of samples and could maintain a relatively
hydrophobic surface during weathering. No statistically significant differences were found in
the effect of sample cut on timber species surface wettability. Although only long term
exposure studies and using substantially more samples can confirm its weathering
performance, the results of this exploratory weathering study indicated that Colorado can
successfully be used as a substitute decking material for Balau. / AFRIKAANSE OPSOMMING: Balau, ‘n houtsoort wat ongeveer 21 Shorea-spesies verteenwoordig, word wyd in
buitenshuise aanwendings benut. In Suid-Afrika is Balau een van die mees gewilde materiale
wat vir dek-doeleindes gebruik word. As gevolg van die toenemende skaarsheid van Balau, is
dit van ekonomiese belang om die gebruik van ‘n moontlik plaasvervangende houtsoort vir
dek-materiaal te ondersoek. Colorado, ‘n mengsel van een of meer van die volgende:
Eucalyptus camaldulensis, Eucalyptus tereticornis en hibriede daarvan, kan as ‘n moontlike
plaasvervanger gebruik word. Hierdie twee spesies en hulle hibriede word op groot skaal in
lande soos Australië, Indië en dele van Suid-Amerika gekweek vanweë hul kort rotasieperiode
en goeie aanpasbaarheid by ‘n wye verskeidenheid grond- en klimaatsfaktore. Die spesies is
aanvanklik as grondstof in die pulp- en papierbedryf gebruik maar word tans al hoe
belangriker in strukturele aanwendings soos byv. meubels, vloer- en dek-materiaal. Die doel
van hierdie verkennende studie was om relevante materiaaleienskappe te ondersoek en om die
versnelde en natuurlike verweringsgedrag van Colorado en Balau vas te stel om sodoende ‘n
aanduiding van die geskiktheid van Colorado as dek-materiaal te kan kry.
Daar is gevind dat Colorado kleiner vat-lumina, minder vate/m2 en kleiner strale as Balau
besit en dat Colorado ‘n hoër digtheid het as Balau. Alhoewel beide houtsoorte relatiewe lae
veselversadigingspunte (VVP) besit, is Colorado se VVP 2.3% persentasiepunte hoër as dié
van Balau. Die swellingskoëffisiente (radiaal en tangensiaal) van Colorado is effens hoër as
dié van Balau, maar Colorado se laer swellingsanisotropie kan op ‘n kleiner neiging tot
skeeftrek dui. Colorado het ‘n hoër wateroplosbare ekstrakstofinhoud as Balau bevat, wat tot
aanvanklik vinnige kleurveranderings kan lei wanneer die hout sonder oppervlaktemiddel
blootgestel word.
Die verweringsgedrag van Colorado en Balau is ondersoek deur monsters aan versnelde en
natuurlike verwering bloot te stel. Eersgenoemde is in ‘n QUV versnelde verweringsapparaat
uitgevoer en laasgenoemde in ‘n binnelandse en ‘n mariene lokaliteit. Tydens verwering het
Colorado ‘n effens hoër kleurverandering ( E*) as Balau getoon. Balau het ‘n hoër toename
in rofheid (Rz), oppervlaktekrake en kraakvorming as Colorado getoon. Colorado het effens
meer kromgetrek terwyl Balau meer skeefgetrek het as Colorado. Geen statisties beduidende
verskille kon tussen die waterwerende eienskappe van die twee houtsoorte vasgestel word nie.
‘n Oppervlakbedekking was effektief om die aanvanklike toename in waterwerende vermoë te
verhoog en gedurende verwering te kon behou. Geen statisties beduidende verskille kon
tussen die invloed van snit van die monster op die oppervlaktebenatbaarheid van die
houtsoorte vasgestel word nie. Alhoewel slegs langtermyn blootstellingstudies en die gebruik
van beduidend veel meer monsters die verweringsgedrag kan bevestig, dui die resultate van hierdie verkennende ondersoek aan dat Colorado suksesvol as ‘n plaasvervangende dekmateriaal
vir Balau gebruik kan word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4202 |
| Date | 03 1900 |
| Creators | Smit, Norman Hein |
| Contributors | Rypstra, T., Terziev, N., Vermaas, H. F., University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Format | 130 p. : ill. |
| Rights | University of Stellenbosch |
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