Attention to surface prep ensures the fairing compound will adhere to the surface and stay in place once it’s cured.

Clean
If the surface isn’t clean, sanding will grind dirt, wax, and other contaminants deeper into the substrate, compromising the effectiveness of the fairing compound, and subsequent primers and topcoats. Clean the surface with a solvent, such as acetone or denatured alcohol, using clean rags and the two-rag wipe on/wipe off method: one rag to apply, one rag to remove. Change rags often so you aren’t smearing contaminants or residue over the surface.

(Optional) Grind
Any surface cracks, crazing (micro-cracks), or gelcoat blisters need to be ground out and have their edges beveled using a right angle grinder or a rotary tool with a right angle attachment. Grinding and beveling roughs up the surface so the fairing compound can achieve a sound mechanical bond. The repair will look better and last longer.

Sand
If necessary before sanding, mask any areas that you do not want to be roughed up. Roughing up the surface by sanding helps the fairing compound adhere better. Use 60-180 grit sandpaper, and sand down to solid material.

Clean Again
If not using a dustless sander, remove all sanding residue with a vacuum cleaner. Clean the area again with acetone or denatured alcohol, and allow the solvent to flash.

Additional Surface Prep Considerations:

Wood

Wood is a very absorbent material, so if you’re using an epoxy fairing compound made with a liquid epoxy resin system, you need to ensure the compound achieves a sound bond on this porous surface. Before applying the compound, brush on a thin coating of properly mixed (that is, resin and hardener only) epoxy resin to first wet out the area to be faired. Then you can do one of two things:

• Wait for the wet-out coat to cure, sand to ensure sufficient key (roughness for mechanical bond), remove sanding residue, and apply the fairing putty.
• Or, you can apply the fairing putty to the wet-out surface once the surface is tacky to the touch.

Metal

Before applying fairing compound to a cleaned metal surface, an etching primer is needed to ensure proper adhesion. For best results, follow all manufacturer’s directions for the etching primer.

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