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Sjökvist, T. (2019). Coated Norway Spruce: Influence of Wood Characteristics on Water Sorption and Coating Durability. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Coated Norway Spruce: Influence of Wood Characteristics on Water Sorption and Coating Durability
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood used outdoors is often degraded and discoloured by microorganisms as a natural part of its life cycle, particularly when exposed to high levels of moisture for prolonged times. In this case, the application of a coating (i.e. paint) is an option for increasing the service life of the wood.

Norway spruce (Picea abies (L.) Karst.) is commonly used for outdoor applications in Sweden. Earlier studies have shown that uncoated spruce heartwood is less prone to moisture sorption in outdoor exposure, resulting in lower moisture content (MC) levels, as compared to sapwood. However, studies related to the above mentioned characteristics are rather limited for coated spruce, especially including the influence of outdoor exposure (i.e. weathering).

The aim of this thesis is, therefore, to increase the knowledge of how heartwood and sapwood of different densities influence on the durability of coated Norway spruce for outdoor use. Different types of coatings with alkyd-, acrylic-, flour- (calcimine paint), or linseed-oil-based resin were included. The objectives were to study the water sorption (including MC variation) behaviour and crack formation of uncoated and coated heartwood and sapwood of different densities.

Furthermore was an objective to study the microbial growth on the surface of similar samples of coated spruce in outdoor exposure. The used methods included wetting and liquid permeability experiments, accelerated water absorption (with samples floating freely in water), and outdoor field test. The field method lasted between three to five years and involved monitoring of the MC variation, the crack formation and the microbial growth on the samples.

The results based on wetting measurements using octane as the adsorbed liquid showed no difference in liquid permeability between the spruce heartwood and sapwood samples of comparable densities, and indicated a similar level of pit aspiration (closure). The common flow path between two cells of conifers occurs through the pits. Still, the sapwood samples had in general a clearly higher water sorption rate than heartwood samples. It could be concluded that the increased sorption was presumably caused by a lowered water surface tension, most likely by a contamination effect of the water by surface-active sapwood extractives rather than differences in morphology of heartwood and sapwood.

However, no clear difference in water absorption and MC levels was seen between coated heartwood and sapwood in the field study or in the accelerated water absorption study. Thus, it is suggested that a coating hinders the surfaceactive extractives to lower the water surface tension, resulting in a similar water absorption behaviour of coated heartwood and sapwood. The influence of density on water sorption of coated spruce was similarly to uncoated spruce, meaning the low-density samples had a higher MC than the high-density samples in the field tests. Furthermore, a one-year weathering of the coated and uncoated samples caused a larger increase in water sorption of high-density heartwood in the accelerated water absorption study.

The field study on uncoated and calcimine-coated spruce showed a higher number of cracks on the high-density samples than on the low-density samples. Additionally, within each density group, a larger number of cracks were seen on sapwood samples as compared to heartwood samples. High-density samples with an alkyd- or an acrylic coating also showed a higher number of cracks. As expected, the formation of cracks on the samples increased their water sorption significantly. The microbial growth was higher on sapwood than on heartwood samples with a white coloured alkyd coating.

The main conclusion is that heartwood and sapwood of different densities influence the water sorption and durability of coated Norway spruce. However, the principles in water sorption of uncoated heartwood and sapwood could not be applied to coated samples. Overall, the results point out that low-density heartwood could be the best material combination to improve the durability of coated spruce in outdoor use. The knowledge acquired in this thesis can enable an increased service life of coated spruce in outdoor use. The increase in service life is achieved by a careful selection of the wood material regarding the proportion of heartwood and to the choice of wood density. As a concluding remark, the role of surface-active spruce extractives needs to be explored, and a follow-up investigation in the context of water sorption is suggested for future research.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2019. p. 56
Series
Linnaeus University Dissertations ; 344
Keywords
Heartwood, Sapwood, Wood extractives, Moisture content, Paint, Alkyd, Acrylic, Linseed oil, Calcimine paint, Mould, Fungi, Algae, Weathering
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-80768 (URN)978-91-88898-39-5 (ISBN)978-91-88898-40-1 (ISBN)
Public defence
2019-03-13, Södrasalen, Hus M, Växjö, 13:00
Opponent
Supervisors
Available from: 2019-02-21 Created: 2019-02-21 Last updated: 2019-03-06Bibliographically approved
Sjökvist, T., Niklewski, J. & Blom, Å. (2019). Effect of wood density and cracks on the moisture content of coated Norway spruce (Picea abies (L.) Karst.). Wood and Fiber Science, 51(2), 160-172
Open this publication in new window or tab >>Effect of wood density and cracks on the moisture content of coated Norway spruce (Picea abies (L.) Karst.)
2019 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 51, no 2, p. 160-172Article in journal (Refereed) Published
Abstract [en]

A protective coating is often used on the cladding of wooden facades to limit the absorption of moisture. Low wood moisture content (MC) is essential to obtain satisfactory durability performance. Wood density is known to influence the water sorption and crack formation of uncoated wood. However, the effect of density on the aforementioned behaviors of coated spruce is not yet fully understood. Six-years of data on the crack formation and the MC variation of outdoor exposed panels are analyzed in this article. The outdoor test was complemented by a subsequent laboratory experiment, wherein the MC variation was monitored at different depths on the board during artificial water spraying. The aim of this research was to increase the knowledge about how wood density and aging affect the water sorption of coated spruce through the crack formation. The results indicated that wood density had an impact on the overall sorption behavior of coated spruce. Low-density spruce contributed to faster water absorption and desorption processes than coated samples with higher density. However, the observed correlation to density was limited to a condition with an intact coating. High-density characteristics contributed to more crack formation, and the density–sorption relationship reversed with a cracked coating. A cracked coating caused a strong local increase in the MC of the wood at the location of the cracks. Weather-exposed replicates without cracks had a higher MC in the core of the board compared with the value beneath the coating. The higher MC is probably due to the water sorption of the uncoated backside of the panel. Such an occurrence raised awareness for future studies to account for multidimensional sorption behavior from all sides of the panel. The local difference in MC also raises awareness for future studies to investigate local MC variations (as opposed to the global average of the panel) in research on the durability of coated wood.

Place, publisher, year, edition, pages
Society of Wood Science and Technology, USA, 2019
National Category
Wood Science Other Materials Engineering
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-81577 (URN)10.22382/wfs-2019-017 (DOI)
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-08-28Bibliographically approved
Sjökvist, T. & Blom, Å. (2019). The influence of coating color, heartwood and sapwood, on moisture content and growth of microorganisms on the surface during outdoor exposure of Norway spruce boards. Journal of Coatings Technology and Research, 16(3), 819-826
Open this publication in new window or tab >>The influence of coating color, heartwood and sapwood, on moisture content and growth of microorganisms on the surface during outdoor exposure of Norway spruce boards
2019 (English)In: Journal of Coatings Technology and Research, ISSN 1547-0091, Vol. 16, no 3, p. 819-826Article in journal (Refereed) Published
Abstract [en]

The use of wood contributes to the global transformation into a bio-based community. There are, however, challenges. The growth of mold, rot fungi, and algae on the coated surface is of major concern due to decreased aesthetic service life and shorter maintenance intervals. The colonization of a coated surface requires the presence of spores, nutrients, and a sufficient amount of water. This work studied the influence of using heartwood and sapwood on the moisture content (MC) and growth of microorganisms on the surface of coated Norway spruce boards [Picea abies (L.) Karst.]. The results revealed a relationship of heartwood samples having a lower MC and a lower or equal degree of biological growth on the coated surface than sapwood samples. The relationship was valid through a range of densities (309–548 kg/m3) and two different coating systems based on either an alkyd or an acrylic resin. Furthermore, the choice of coating color (red compared to white) affected the MC as the red-colored samples had a lower MC, combined with no growth of microorganisms.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Mold Fungi Algae Durability Cladding
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-79712 (URN)10.1007/s11998-018-00165-3 (DOI)000466347800017 ()2-s2.0-85060156167 (Scopus ID)
Available from: 2019-01-22 Created: 2019-01-22 Last updated: 2019-08-29Bibliographically approved
Sjökvist, T., Blom, Å. & Wålinder, M. (2019). The influence of heartwood, sapwood and density on moisture fluctuations and crack formations of coated Norway spruce in outdoor exposure. Journal of Wood Science, 65(1), 1-9, Article ID 45.
Open this publication in new window or tab >>The influence of heartwood, sapwood and density on moisture fluctuations and crack formations of coated Norway spruce in outdoor exposure
2019 (English)In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 65, no 1, p. 1-9, article id 45Article in journal (Refereed) Published
Abstract [en]

The moisture sorption behaviour of wood strongly influences the durability of exterior-coated wood. Wood characteristics are known to influence the water sorption of uncoated wood. Despite this, the majority of the research on coated wood has been focused on the coating properties. This study aims to investigate the impact of heartwood, sapwood and density on the moisture content (MC) and crack formation of coated Norway spruce (Picea abies (L.) Karst.). Boards with film-forming coatings or a non-film-forming coating were exposed outdoors during 3 years. Crack development and the mass of the boards were recorded during this period. Heartwood and sapwood samples showed no differences in MC. Thus, a coating seems to reduce the differences in water sorption behaviour that is present in uncoated heartwood and sapwood spruce. The reduction is probably related to wetting properties and different sorption mechanisms, involving free and bond water diffusion. However, the low-density samples had significantly higher MC levels than the high-density samples. The high-density samples with a non-film-forming coating showed a higher number of cracks than those with lower density. Furthermore, sapwood samples had a remarkably high number of cracks when compared to the corresponding heartwood samples, despite a similar density and MC.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-89196 (URN)10.1186/s10086-019-1825-1 (DOI)000486489400001 ()
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-10-03Bibliographically approved
Sjökvist, T., Wålinder, M. E. .. & Blom, Å. (2018). Liquid sorption characterisation of Norway spruce heartwood and sapwood using a muiticycle Wilhelmy plate metho. International Wood Products Journal, 9(2), 58-65
Open this publication in new window or tab >>Liquid sorption characterisation of Norway spruce heartwood and sapwood using a muiticycle Wilhelmy plate metho
2018 (English)In: International Wood Products Journal, ISSN 2042-6445, E-ISSN 2042-6453, Vol. 9, no 2, p. 58-65Article in journal (Refereed) Published
Abstract [en]

A multicycle Wilhelmy plate method was applied to study the water and octane sorption behaviour of small Norway spruce veneers. Dry heart- and sapwood samples of varying density were investigated. The results showed a correlation between the porosity and the sorption of octane for all samples, i.e. a higher wood porosity resulted in higher octane sorption. However, no difference in octane sorption was found between heart- and sapwood samples of similar density. The water sorption behaviour was difficult to interpret, probably due to the influence of surface-active wood extractives. It is suggested that the presence of such extractives, particularly in the sapwood samples, increases the sorption of water due to a significant decrease in its apparent surface tension. Hence, the results indicate that the liquid water sorption of spruce heart- and sapwood is strongly influenced by variations in the extractives content rather than by the micromorphology.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Picea abies, water, octane, extractives, permeability, pit aspiration, coating, durability
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-73984 (URN)10.1080/20426445.2018.1467602 (DOI)000440888400004 ()2-s2.0-85046402339 (Scopus ID)
Funder
Swedish Research Council Formas, EnWoBio 2014-172
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2019-08-29Bibliographically approved
Sjökvist, T. & Blom, Å. (2017). Utomhusexponering av ytbehandlat trä: Undersökning av trämaterialets påverkan på beständigheten hos en målad granpanel. Växjö: Linnéuniversitetet
Open this publication in new window or tab >>Utomhusexponering av ytbehandlat trä: Undersökning av trämaterialets påverkan på beständigheten hos en målad granpanel
2017 (Swedish)Report (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Växjö: Linnéuniversitetet, 2017. p. 46
Series
Rapporter: Fakulteten för teknik, Linnéuniversitetet ; 50
Keywords
Gran, Målad panel, Utomhus, Beständighet, Linolja, Alkyd, Akrylat, Slamfärg
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-71485 (URN)978-91-88357-97-7 (ISBN)
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-03-15Bibliographically approved
Sjökvist, T. & Blom, Å. (2016). Influence of some wood characteristics on the variation of moisture content in outdoor exposed coated Norway spruce panels. In: : . Paper presented at 70th International convention Portland, Oregon, USA, June 27-29, 2016. Forest Products Society
Open this publication in new window or tab >>Influence of some wood characteristics on the variation of moisture content in outdoor exposed coated Norway spruce panels
2016 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A field test of coated spruce was exposed outdoors during three years, measuring the influence of wood characteristics on the variation of moisture content in coated panels. Wood samples had following characteristics: fast-grown or slow-grown wood, heartwood or sapwood. Three different film-forming coatings were tested and all samples were exposed above ground on racks. The measured moisture contents were evaluated using the statistical method Principal Component Analysis (PCA). The moisture content of the coated samples was clearly influenced by wood characteristics; fast-grown wood had higher moisture content and higher moisture fluctuation than slow-grown wood in each respective coating system. The choice of coating system also affects the wood moisture content. The result indicates that in order to achieve low moisture content- excluding the effectiveness of coatings, wood characteristics should also be considered.

Place, publisher, year, edition, pages
Forest Products Society, 2016
Keywords
Exterior coating, Moisture content, Heartwood, Sapwood, Fast-grown, Slow-grown, Alkyd, Acrylate
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-56684 (URN)
Conference
70th International convention Portland, Oregon, USA, June 27-29, 2016
Projects
The Bridge
Available from: 2016-09-23 Created: 2016-09-23 Last updated: 2017-01-17Bibliographically approved
Sjökvist, T. & Blom, Å. (2016). The impact of heartwood and sapwood on biological discoloration of a painted surface. In: Bruno Andersons, Arnis Kokorevics (Ed.), Proceedings of the 12th meeting of the Northern European Network for Wood Science and Engineering (WSE): Wood science and engineering - a key factor on the transition to Bioeconomy. September 12-13, 2016, Riga, Latvia. Paper presented at 12th Northern European Network for Wood Science and Engineering (WSE) ,Riga, Latvia, 12-13 September, 2016 (pp. 137-142). Riga: Latvian State Institute of Wood Chemistry
Open this publication in new window or tab >>The impact of heartwood and sapwood on biological discoloration of a painted surface
2016 (English)In: Proceedings of the 12th meeting of the Northern European Network for Wood Science and Engineering (WSE): Wood science and engineering - a key factor on the transition to Bioeconomy. September 12-13, 2016, Riga, Latvia / [ed] Bruno Andersons, Arnis Kokorevics, Riga: Latvian State Institute of Wood Chemistry , 2016, p. 137-142Conference paper, Published paper (Other academic)
Abstract [en]

Wood material has advantages, it comes from a renewable source and it is easy to manage. But one disadvantage when used outdoors is biological discoloration of the material. Some impact on the discoloration is the presence of moisture and nutrients, necessary components for the microorganisms to grow and start a colonisation. Samples made of Norway spruce (Picea abies (L.) Karst) heartwood or sapwood coated with two different film forming paints was studied. The paints had a binder formula made of alkyd or acrylate. Additional parameters related to study the influence of moisture content on discoloration were high and low density material, with and without impregnation oil. Outdoor exposure was made during five years in the southern part of Sweden. The samples were hung with 45 degree inclination, facing south direction. Visual differences in biological surface discoloration were observed for samples within the same paint, which could be explained by differences in heartwood and sapwood.

Place, publisher, year, edition, pages
Riga: Latvian State Institute of Wood Chemistry, 2016
Keywords
Discoloration, Heartwood, Sapwood, Paint
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-56687 (URN)978-9934-14-981-8 (ISBN)978-9934-14-982-5 (ISBN)
Conference
12th Northern European Network for Wood Science and Engineering (WSE) ,Riga, Latvia, 12-13 September, 2016
Available from: 2016-09-23 Created: 2016-09-23 Last updated: 2017-04-13Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4760-3787

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