A fairing compound is typically composed of epoxy resin and low-density fillers, and is used to fill and shape low areas on surfaces like fiberglass, wood, steel, and aluminum. Fairing a surface creates a fair appearance that looks and feels smooth while blending with the surrounding area.
Fairing compound is often used prior to fiberglassing to ensure an even surface, and because it sands easier than fiberglass. Surface fillers, fairing compounds, and repair compounds are used to fill large cavities, cover large areas, and provide a smooth surface for subsequent processes. Fiberglass hulls frequently require minor touch up repairs to address scratches and other surface defects like small hull dents, dings, and gouges prior to priming and painting the surfaces.
Common repairs below the waterline, like reshaping and fairing a boats rudder and keel, or filling holes after grinding down gelcoat blisters, are very common fairing applications.
Each type of fairing compound contains an epoxy, polyester, or vinyl ester resin. Each resin is designed for specific boat construction and repair tasks.
In addition to the resin, each compound contains a substance designed to activate the resin and ensure that it cures to a hard plastic material. For example, epoxy resin is paired with a hardener. Polyester and vinyl ester resins depend on a catalyst to complete the curing process. Always use the manufacturer-specified amounts of hardener or catalyst, or the resin will not cure as intended.
All fairing compounds also feature a filler component. For example, an epoxy resin-based fairing compound contains fumed silica. Polyester- and vinyl ester-based compounds generally contain fiberglass strands or chopped fiber, both intended to thicken the putty so it will not sag or run.
Every fairing compound also contains an additive, such as glass microballoons, that makes sanding easier after it cures.
Yes! Making your own fairing filler lets you customize the fillers properties. You will need an appropriate epoxy resin system, thickener like colloidal silica, and microballoons to make it easier to sand. Tip: always mix resin and hardener before adding additives or filler to the mixture. In general, a pre-mixed, pre-packaged product is a faster, easier, and less expensive method.
Compatible with fiberglass, wood, and metal boat hulls when primer and/or paint are applied over the compound. It can be used below or above the waterline. Compared to the other resin types, epoxy resin-based compounds provide improved adhesion, superior strength, and more resistance to water penetration (also called osmosis). This is the best fairing compound for wooden boats.
Ideal for above-the-waterline fairing on fiberglass boats. These compounds also excel at filling dents, dings, and gouges. After applying the compound, the user must finish the surface with gelcoat or prime using an epoxy primer, and then paint with a topcoat.
Used for fairing above or below the waterline on fiberglass vessels. Vinylester resin also fills dings, dents, and gouges. After the fillers are applied, the surface must be finished with gelcoat or primed and painted. Compared to polyester resin, vinylesters show less cracking and shrinkage.
Bondo type fillers cannot be compared to marine fairing compounds, as Bondo is not waterproof, and lacks the strength of marine epoxy and vinyl yester repair products. It should not be used below the waterline.
To prep the surface, you will use tools like an angle grinder, and a rotary tool like a Dremel. You will need a trowel or spreader, notched spreader, a scraper, sanding block, flexible long board sander (the long board makes sanding large areas a lot easier) to sand afterwards, and sandpaper.
Generally, 60 to 180 grit sandpaper is used for surface prep, and 220 to 320 to sand cured compound smooth. Be sure to mask off adjacent areas with a good tape that allows clean removal. Use clean rags and denatured alcohol to wipe down surfaces. Always protect yourself by wearing a suitable NIOSH approved respirator, eye protection, protective clothing, and gloves.
Begin with a clean surface to improve adhesion, and will also ensure that the compound remains in place after it is cured.
Yes, you can apply fairing compound over gelcoat. Sand the hull and wipe it down before application. Note that polyester fairing compound is only designed for above-the-waterline use. Epoxy fairing compound is suited for above-the-waterline and below-the-waterline applications.
Gelcoat should not be applied directly over epoxy fairing compounds like TotalFair. Doing so will result in the gelcoat failing to cure properly. In order to gelcoat over fairing compound, you need to first apply a 2-part epoxy primer.