U-POL Fiberglass Filler 3L — Ready-to-Mix Polyester Repair Kit with BPO Paste, High-Build & Sandable

This two-part kit combines a high-build, sandable polyester filler with U-POL's benzoyl peroxide (BPO) paste catalyst to deliver controlled cure times and a strong, conformal finish. Formulated for automotive, marine and composite repairs, the filler lays on smoothly, sands to a feather-edge and accepts topcoats. The separate BPO paste lets you adjust working time and ensures thorough crosslinking when mixed at the recommended ratio.

What makes this fiberglass filler suitable for structural and cosmetic repairs?

The U-POL 0700 filler offers a balance between filling strength and sandability. Its polyester chemistry bonds well to prepared fiberglass laminates and gelcoat, providing a stable base for finishing layers without excessive shrinkage.

• High-build formulation for deep fills and profile shaping
• Good adhesion to fiberglass, gelcoat and primed substrates
• Controlled shrinkage for consistent finish thickness
• Sands easily to a smooth feathered edge

How do I mix and control cure time with the BPO paste?

Mixing is done by adding the BPO paste to the polyester filler in the manufacturer’s recommended ratio, then stirring until uniform. Adjusting the amount of catalyst and working temperature changes pot life and cure speed—less catalyst = longer working time; more = faster set.

• Use recommended paste weight percent for standard pot life
• Work at moderate temperatures for predictable curing
• Mix thoroughly to avoid soft spots or incomplete cure
• Wear gloves and avoid skin contact with uncured material

Which surfaces and prep steps give the best results?

Best performance comes from mechanically abrading the repair area, removing contaminants, and wiping with a suitable solvent. For delaminations or holes, backing with a glass mat and building layers of filler creates a strong repair.

• Abrade to sound substrate; remove wax, oil and loose material
• Use glass mat or woven roving for structural fills under the filler
• Apply in layers, allowing each to tack before adding more
• Finish with progressive sanding grits before priming and topcoat

What safety and handling practices should I follow?

Both polyester fillers and BPO catalysts are reactive chemicals; handle with care, use PPE, and ensure good ventilation. Store the BPO paste in a cool, dry place away from heat sources and incompatible materials.

• Wear nitrile gloves, safety goggles and a respirator during mixing
• Work in well-ventilated areas to minimize styrene fumes
• Clean tools immediately after use to prevent cured build-up
• Follow local regulations for disposal of unused catalyst and resin

Who is this for: U-POL 0700 Fiberglass Filler with BPO paste is intended for professional bodyshops, marine repair technicians and advanced DIYers who need a dependable polyester repair system. It suits projects from gelcoat repairs and fairing compounds to medium structural rebuilds where a sandable, paint-ready surface is required. If you require epoxy-level structural bonding or underwater repairs, consider a purpose-built epoxy system instead; for conventional fiberglass and GRP repairs, this kit is a practical, widely used solution that balances strength, workability and finishability.