Colour as a quality indicator for industrially manufactured ThermoWood®

Figures & data

Table 1. Colour guidelines for ThermoWood® Norway spruce and Scots pine as currently defined within Finotrol (2017). Colour values for untreated timber (newly planed surfaces) are given as a reference. Temp. and Time – treatment temperature and time in phase 2 of the process, MC is moisture content at colour measurements and EMC equilibrium MC at 20°C and 65% RH.

Class	Temp. (°C)	Time (h)	MC (%)	EMC (%)	L*	a*	b*
Thermo-S	190 ± 3	2–3	4–7	6–8	58–68	8–10	–
Thermo-D	212 ± 3	2–3	4–7	4–6	45–55	–	19–24
Untreated Norway spruce	–	–	18	12	82 ± 1.2	4 ± 0.9	19 ± 1.7
Untreated Scots pine	–	–	18	12	84 ± 0.8	4 ± 1.4	19 ± 1.7

Table 2. Process conditions for the 12 ThermoWood® process plants studied between 2007–2018. Kiln size: small < 20 m³, medium 20–60 m³, large > 60 m³.

Plant No.	Year of measurements	Initial MC	Species	Thickness (mm)	Process control	Size of kiln
1	2010–2012, 2015–2017	pre-dried/green	pine	25, 32	wood	small
2	2007–2008, 2013–2014, 2016, 2018	pre-dried/green	pine	32	air	large
3	2009–2010, 2013, 2016	pre-dried	pine, spruce	25,32, 38, 50	wood	small
4	2010, 2012–2016, 2018	pre-dried	pine, spruce	25, 32, 38, 50	wood	large
5	2009–2011, 2014, 2016–2018	pre-dried	pine, spruce	25, 32, 38, 50	wood/air	large
6	2010–2011, 2013–2015, 2017	pre-dried	pine, spruce	25, 32, 50	wood	small
7	2011, 2013–2014, 2017	pre-dried	pine, spruce	25, 38, 50	wood	large
8	2008, 2010–2011, 2013, 2016	pre-dried	pine, spruce	32, 38, 50	wood	small
9	2010–2011, 2016	pre-dried	pine	25	air	medium
10	2014	pre-dried	spruce	25, 38	air	large
11	2015, 2018	pre-dried	pine	25	wood	large
12	2018	pre-dried	pine, spruce	25, 32	wood	large

Figure 1. Average colour-measurement data and their standard deviations for ThermoWood® Thermo-D Norway spruce and Scots pine.

Finotrol (2017) FC-2. Thermally Modified Timber (TMT) (Mikkeli: Finotrol Oy), 13 pp.

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