A beautiful paint job is 90% preparation and only about 10% actual painting. The professionals put their greatest effort into prep, and so should you. Here are seven basic steps for preparing your surface with the right prep and cleaning supplies.

1. Wash, De-Wax Twice, and Wash Again

Start by cleaning the hull with soap and water, rinse thoroughly, and let dry. Follow up by applying a de-waxing solvent 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 the old wax over the surface. Repeat the dewaxing process. Finally, wash the hull thoroughly with a strong detergent such as TSP (trisodium phosphate) to remove any last traces of wax.

If the surface isn’t clean, sanding will drive dirt, wax, and other contaminants deeper into the substrate, compromising the quality of the finish. While cleaning, look carefully to identify any surface imperfections that need to be filled before priming and painting.

2. Fill Dents and Gouges

New paint will only hide the old color–not the old dings and dents, and will actually make imperfections stand out. Although a high-quality topside primer does have some minor filling abilities, it’s best to use a quick-drying, easy-sanding fairing compound to fill any surface imperfections first.

Apply the fairing putty. If using an epoxy fairing putty, apply it proud so it stands above the surrounding surface. This way it’s easier to sand down smooth after drying. To fair and smooth it, use a random-orbit sander. Start with heavy grit sandpaper to rough sand the area. For the final smoothing and contouring, switch to finer grit paper. Once you reach 220-grit, you’re ready for primer.

3. Sand and Wipe

This initial sanding is to prepare for application of the primer. Sand fiberglass or gelcoat, previously painted surfaces in good condition, or previously painted wooden boats with 220-grit sandpaper. For wood, use 180 grit and sand down to 220. After sanding, wipe the surface down with the solvent recommended by the primer manufacturer, for example, xylene or mineral spirits, and let flash.

4. Priming

Primer provides a solid foundation for subsequent coats of paint by doing the following:

1. Bonding to the underlying surface, and allows the topcoat to achieve a sound mechanical bond with it.
2. Sealing and hiding any repairs. Some higher solids primers even fill small scratches.
3. Separating the old topside paint from the new preventing any adverse chemical reaction.

5. Sanding Again

Lightly sand the primed surface with 220 or 320-grit sandpaper, or the grit recommended by the coating manufacturer. If hand-sanding, take care and use a sanding block or flexible longboard sander so you sand evenly and don’t create any unintentional dips in the surface.

If sanding with a random-orbit sander, set the mode switch to "random orbit" action (for finish sanding), not "random orbit with forced rotation" action (for aggressive sanding and polishing). It’s also very important to hold the sander flush with the surface and keep it moving to prevent swirl marks and dishing (low spots).

6. Masking

Certain masking tapes tear easily and leave traces of residue on removal. Use a high-quality masking tape that removes cleanly to protect non-painted surfaces. For taping curved surfaces, use a durable, flexible tape that lets you lay down a clean line quickly and easily.

7. Wiping Again

Ensure that any hand or fingerprints from masking, and any final traces of dust are removed prior to painting. Wipe the surface with a clean, lint-free rag soaked in mineral spirits, or the paint manufacturer’s recommended solvent, and allow to dry completely. Take care not to touch the surface before painting because the cure will be affected by any contaminants.

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