Microdrill

Overview

A Microdrill assessment is a form of advanced decay detection used to evaluate the internal structural integrity of trees. It involves using a high-resolution, mechanical drilling tool (commonly a Resistograph) to measure the resistance of wood as a fine drill bit penetrates the stem, root collar or major limbs.

Purpose

Microdrill testing is used to:

• Detect internal decay, cavities, or hollows not visible from the outside.
• Measure residual wall thickness and structural soundness.
• Distinguish between healthy wood, compromised tissue and voids.
• Support risk assessments and management decisions for valuable, mature or high-risk trees.

Methodology

• A very thin drill bit (approx. 1.5 mm) is driven slowly into the tree.
• The resistance to drilling is recorded digitally and plotted as a graph.
• High resistance indicates solid, sound wood; low resistance suggests decay, rot or cavities.
• The procedure causes minimal damage to the tree – only a small, self-healing hole is left.

Typical Outputs

• Graphical trace showing wood resistance at various depths.
• Interpretation of findings by a qualified arborist or tree risk assessor.
• Recommendations based on structural condition (e.g., monitoring, pruning, reduction or removal).

Microdrill assessments are commonly used alongside Visual Tree Assessment (VTA), PiCUS Sonic Tomography, or Load Analysis to provide a full picture of a tree’s condition, especially where decay is suspected but not externally visible.