Active Thermography in Diagnostics of Timber Elements Covered with Polychrome

Area of Science:

• Materials Science
• Non-Destructive Testing
• Wood Science

Background:

• Natural wood defects like knots significantly impact structural timber strength.
• Accurate assessment of timber condition is crucial for historic building preservation.
• Existing methods for evaluating timber defects can be limited, especially with surface coatings.

Purpose of the Study:

• To evaluate active thermography for determining the knot area ratio (KAR) in painted timber.
• To assess the effectiveness of different energy sources for active thermography in wood.
• To establish active thermography's utility in guiding semi-destructive testing (SDTs) on historic timber.

Main Methods:

• Active thermography was applied to timber specimens (fir, pine, spruce) with varying paint coatings.
• Three external energy sources were utilized: laboratory dryer, air heater, and halogen lamps.
• Thermal images were analyzed to estimate KAR based on temperature differentials between knots and wood.

Main Results:

• Active thermography successfully enabled the estimation of KAR in painted timber elements.
• The choice of external energy source and operator judgment influenced the results.
• Thermal imaging provided effective localization for subsequent SDTs.

Conclusions:

• Active thermography is a viable non-destructive method for assessing KAR in painted structural timber.
• The technique aids in identifying areas requiring further investigation through SDTs.
• This approach supports the technical assessment of historic structural elements with polychrome finishes.