How to Prepare your Boat for Painting a Gelcoat

If the gelcoat is in good condition with no major cracking or crazing, the job is relatively straightforward—clean and prepare the surface, apply an epoxy primer, sand the primer, remove the sanding residue and then apply the topcoat.
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Proper preparation is key. Photo courtesy of Mark Corke

Proper preparation is key. Photo courtesy of Mark Corke

So, the gelcoat on your boat is looking chalky and faded. You’ve cleaned, compounded and waxed, and it looks good for a while, but the chalkiness returns—maybe the red accent stripe that used to look so good looks pink, or the dark blue bootstripe is now baby blue. If so then it’s time to think about refinishing the gelcoat.

As gelcoats age they lose their luster and become chalky and porous. They also become brittle, and crazing will begin to appear in areas where the boat flexes. At first the crazing will appear like it does on old china, where you can see the crack but cannot feel it when you run your finger over it. As the cracking progresses, however, you will begin to feel it, and the crack will keep expanding. This crazing and cracking is different from the stress cracks that occur around stanchions, cleats and other deck hardware.

If the gelcoat is in good condition with no major cracking or crazing, the job is relatively straightforward—clean and prepare the surface, apply an epoxy primer, sand the primer, remove the sanding residue and then apply the topcoat. Gelcoats that are more heavily cracked or crazed will require additional preparation and labor. Areas that have been damaged will require still more labor to repair the surface.

Sanding and cleaning the hull is the first step for any paint job. Photo courtesy of Mark Corke

Sanding and cleaning the hull is the first step for any paint job. Photo courtesy of Mark Corke

At this point, you will want to determine whether you want to do the work yourself or have a professional do it for you. If you want to do it yourself and have applied paint to smaller boats in the past, either with a single part enamel or a two-part polyurethane, then you will already be familiar with the techniques necessary to provide a good finish. One part-finishes are particularly easy to use, being less sensitive to temperature and humidity, and will provide a good finish. On the other hand two-part finishes—while more difficult to apply—have a higher gloss level and keep their color and glossy finish longer. They are also more resistant to abrasion.

If you decide to do the job yourself, there are some other things to consider. How much time will the project take? Do you have that much time? Do you have a good work place, the proper equipment, and the materials that are needed? And finally, and perhaps most importantly, do you have the skill required to do the job properly?

Prepping your topsides is key for a quality finish. Photo courtesy of Mark Corke

Prepping your topsides is key for a quality finish. Photo courtesy of Mark Corke

If you do decide to repair the gelcoat yourself, this is what you’ll need to do. The first step is to clean the surface. Anything that can cause a problem with the finish, such as oil, wax, grease, silicone, dirt, mold or mildew, must be removed prior to sanding. Why? Because not only does sanding not remove surface contamination, it may, in fact, spread the contamination from one area to another. And because of the heat developed when sanding, any wax, oil or grease on the surface may melt into it, making it extremely difficult to get it clean.

Start off by scrubbing the surface with soap and water using a Scotch-Brite pad, and make sure to rinse the soap residue off. If the water sheets off and does not bead up or separate, the surface is clean and ready to be sanded.

Next, inspect the surface and mark any nicks, dings or small scratches with a pencil. Go back and fill these areas with epoxy putty. Many people use a polyester putty for filling, because it dries quickly and is easier to sand. But in my experience it is best to only use polyester putty for small pinholes and use epoxy putty for anything larger—it is more stable and will not shrink or distort the way polyester putty will.

Once the imperfections have been filled, apply one to two coats of a high-build primer and then one to two coats of a finish primer. Final sanding of the finish primer should be done with 320- to 400-grit sandpaper. After sanding, wipe off the residue. Once the surface has been sanded and cleaned, apply two to three coats of finish.

For areas with deep cracking or crazing, start with 36- to 60-grit sandpaper and apply a high-solids epoxy, such as Awlgrip Hullgard. Fill and fair between each coat of primer. If the gelcoat has been damaged to the point where you can see the cloth pattern underneath or it has become delaminated, it will need to be repaired prior to application of primer. If this is the case, in these areas start with a 100 percent solids epoxy such as WEST System Epoxy. After filling and fairing, apply a high build primer.

The point of all this filling, fairing, priming and sanding is to get the surface as smooth and even as possible to provide a blank canvas for the finish—the high gloss of the finish will magnify every imperfection in the hull, and once the finish goes on it will not be possible to go back and repair the surface without removing the finish.

A good Tyvex suit and respirator go a long way when working with coatings. Photo by billy black

A good Tyvex suit and respirator go a long way when working with coatings. Photo by billy black

Before you Begin

A few questions to ask yourself before repairing your gelcoat

How long will it take?

The estimate for the labor on a 45ft boat for the hullsides alone will be between 60 and 80 hours from sanding and prepping through the final coat of primer. Eighty percent of the job is preparing the boat, 20 percent is applying the finish coat. The time it will take a dedicated do-it-yourselfer to apply the finish coat will be at least double that amount. In general, most repair yards estimate the job by the foot, so the estimate for painting the hullsides from the waterline to the gunwale with the gelcoat in good shape and maybe some minor crazing might be around $300 to $500 per foot from start to finish. Decks and anything from the gunwale to the coach roof may be quoted at two to three times the amount of the hullsides, because of the extra labor involved and to cover any surprises they may find. As a rule of thumb, yards generally figure one-third of the cost will be materials and two-thirds will be the cost of the labor.

Do you have the place? 

The best place to work on a boat is inside, where you can control the environment and work in clean conditions. Unfortunately, the best time for painting your boat is also the best time for using it. Much of the prep work is not temperature dependent, so you can clean, sand and maybe even apply primer in less than ideal conditions. Working outside in summer in the south or in winter in the north may not be as fun as it sounds. If you can do the work yourself in a boatyard be sure to follow the Green Marina practices.

Do you have the equipment? 

Sanders and safety equipment are just some of the things you will need. Many paint manufacturers have excellent product information that can be found on their websites, as well as customer service numbers you can call to speak with professionals and get expert advice. Both are great assets, as is going to boat shows and talking with the company representatives that cover your area. The more information you have, the better.

Do you have the skill? 

Primers and fairing compounds will need to be sanded after application, so fear not first-timer: it will be difficult to make a mistake that cannot be corrected

Tools for the Job

Here is a down and dirty list of what you’ll need to take on the job yourself

30ft sailboat waterline to gunwale will approximately require:

1½ Gallons of Primer

2–3 Gallons of High Build Primer

Fairing compound as needed

45ft sailboat waterline to gunwale will approximately require:

4 Gallons of Primer

5–6 Gallons of High Build Primer

Fairing compound as needed

Supply List

High Build Primer $100–$125 per mixed gal

Fairing Compound $110–$125 per mixed gal

Finish Primer $100–$125 per mixed gal

Thinners for the above $40–$70 per gal

1-Part Primers $30/qt–$90/gal

Thinners for the above $12/qt–$42/gal

Safety Equipment

Tyvek Suits $6–$12

Gloves $12/box

Respirators $14–$400

Painting Supplies

Sandpaper

Masking tape ($6–$30 per roll)

Mixing pails

Stirring sticks

Wipe down rags

Tack cloths

Paint strainers

Note: Prices are approximate and may vary depending on location and vendor

Editor’s Note: Stay tuned for part 2 in April, a guide to the best techniques for giving your boat a high-quality finish.

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