Wood Filler Shrinkage Test
Ensure machined filler repairs remain dimensionally stable before final finishing or reassembly by following this strict volumetric shrinkage verification procedure.
To establish a standardized method for evaluating the volumetric shrinkage of two-part epoxy and polyester wood fillers used in pattern making, die modeling, and structural repair prior to coating or machining. This procedure ensures repaired surfaces maintain dimensional integrity under thermal and mechanical stress.
This SOP applies to all high-build wood fillers and body putties utilized in the pattern shop, foundry, and maintenance repair bays. It covers the preparation, casting, measurement, and acceptance/rejection criteria for shrinkage testing of materials applied at depths exceeding 1/4 inch.
- Lockout/Tagout mixing equipment per Plant Standard PS-101 before cleaning or performing setup. Verify zero energy state before reaching into mixing chambers.
- Wear nitrile gloves, safety glasses, and chemically resistant aprons. Ensure adequate ventilation (LEV) is operating to capture styrene and isocyanate vapours below 20 ppm.
- Isolate all ignition sources. Ground mixing containers and molds to prevent static discharge when handling volatile solvents, hardeners, and accelerators.
- Digital micrometer (±0.001 in) or calibrated calliper with NIST traceable certificate.
- Precision-machined aluminum mold cavity (3.0 x 3.0 x 0.5 in).
- Two-part epoxy wood filler (e.g., Smooth-On EA-40) or polyester filler (e.g., Bondo).
- Graduated mixing cups, stir sticks, and a gram scale (resolution ±0.1 g).
- Temperature/humidity data logger with alarm logging capability.
- Mold release agent (PVA or silicone-based).
[(V_initial - V_final) / V_initial] * 100. Acceptable threshold is <0.5% linear shrinkage (or <1.5% volumetric) per the Engineering standard. Tag and quarantine any batch exceeding these limits for engineering review.