# Drying Behaviour of 50 mm Thick Turkey Oak Lumber
## 3 Results
### Air-Drying  
The evolution of the moisture content of the monitored boards throughout the air-drying period is presented in Figure 8.  
It can be noticed that after 7 months of exposure, the Turkey oak lumber eliminated only free water, 12% of its moisture content (from an average of 47% to an average of 35%), thus remaining at a moisture content above the fiber saturation point. The highest drying rate (w = 0.13%/day) was attained in June, but the average over the whole period was only 0.06%/day.  
The moisture gradient across the lumber thickness in Turkey oak decreased from the initial 18% to 5-6% during the winter months, but it increased again a little toward the end of February, when the relative air humidity dropped from 80-90% to 60-70% (see Figure 3).  
According to the obtained results, it can be stated that the air-drying of 50 mm thick Turkey oak lumber allowed the removal of ca. 2% of free water per month from November to April and ca. 4% of free water per month from May to October, in this geographic area (with a continental temperate climate). Under these circumstances, depending also on the initial moisture content, it might take 9-12 months for the 50 mm thick Turkey oak lumber to reach the fiber saturation point.  
This result is in good correlation with data provided by an industrial survey [10], which indicated a duration of 9 months for the moisture content reduction from 45% to 35% in the case of the same species. According to the measured data, the air-drying time could be reduced if the lumber was stacked in March. The drying rate was increased during the spring and summer months, but increases in the moisture gradient across the lumber thickness and case-hardening hindered drying during the same period.  
The obtained results showed that the air-drying of Turkey oak lumber required more than that of European oak or red oak. According to the reference literature, 50 mm thick European oak (_Quercus robur_) dries in 100 days from 50% to 25% when stacked in February and in 70 days when stacked in May [3], and 4/4 red oak lumber needs 2.5 months to dry from 80% to 21% when stacked in March [5].  
The present research did not allow assessing the time needed to air-dry this species below the fiber saturation point.  
The results of the final quality control, when all test boards were visually examined, revealed that 37% of the evaluated boards displayed surface and end cracks. The cracks occurred only on the wide boards (with \(b\) = 30 cm). None of the narrow boards (\(b\) = 15 cm) displayed any type of cracks, neither in the heartwood nor in the sapwood or in the transition area between the sapwood and heartwood. The end-sealing with a paraffin-based sealer was ineffective: 75% of protected pieces displayed end cracks (Figure 9). The case-hardening test confirmed the accumulation of moderate internal stresses through drying) as all evaluated boards recorded a gap opening of 2.5 \(\pm\) 0.5 mm  
Figure 8: Drying diagram for air-dried Turkey oak lumber.  
(medium case-hardening) (Figure 10). Crosscutting the test boards revealed that no internal cracks occurred.