Fairing

Fairing compounds are mixtures of resin (epoxy, polyester, or vinyl ester) and lightweight fillers designed to create a compound that is easily sanded to a smooth, “fair” surface. Their primary purpose is to patch gaps, cracks, dings or dents, and other uneven surfaces while remaining easy to sand.

When fairing as a part of an initial build process, the best practice is to utilize the same resin type with which the component is being constructed. For retrofit and repair work on post-cure resin systems, epoxy will achieve the best bond (even if the part was originally constructed utilizing a polyester or vinyl ester resin system).

The specific characteristics of a compound depend on the filler-to-resin ratio and the types of additives used. Adjust these mixtures to prioritize different properties, such as:

• Density and Strength: Balancing weight against structural integrity
• Sandability: Ensuring the cured material can be easily leveled or “faired”
• Finish and Color: Achieving a specific texture or aesthetic color-match

Common Fillers and Their Roles

• To Extend & Reduce Density (added first)
  • Phenolic Microballoons- Provides lightweight, easy-to-sand volume; distinctive reddish-brown color
  • Glass Bubbles- Another filler utilized for lightweight, easy-to-sand volume; cures to milky-white or more solid white, depending on mix ratio
• To Modify
  • Wood Flour- Adds density and structural body while remaining sandable; great when fairing wood or surfaces similar in color and/or density.
  • Talc- Refines the compound to a texture that can be sanded to a smoother finish
• To Thicken & Reduce Sag (added last)
• • Cab o Sil- Thickens resin compound to prevent sagging; great for working on vertical or near-vertical surfaces

*Pro-Tip: For deeper imperfections, use a mutli-stage approach. Apply fairing compound in layers, or for even larger voids, first fill with compatible core materials (such as foam, wood, or fiberglass) before fairing in thin layers. This prevents excessive exothermic heat buildup, which can compromise the resin during the curing process.