The difference between an amateur and a professional painter is preparation. The amateur focuses on painting. The professional puts most of his efforts into preparing for painting. It is a cliché, but it is also true, that 99 percent of a good paint job lies in the preparation. It does not matter if the boat is wood or fiberglass, preparation work still has to be done. However, remember, paint hides the underlying color, but not texture. The use of sanding surfacers, putties, sealers and sandpaper will have as much to do with the final result as how many coats, or what type of paint you use.
A professionally sprayed two-part urethane topside paint will last five to ten years, but the gloss gradually fades. To maintain a high gloss, a boat should be repainted every five years. If you do not worry about the gloss fading you can leave the paintwork for ten or twelve years. A two-part polyurethane will usually last 2 to 3 times the life of a single part paint.
Painting a boat is not difficult. By purchasing quality marine paints, you are assured of great results as long as you follow the manufacturer's instructions. There are a number of ways to apply paint:
1. Wash and de-wax the surface.
The first step is to wipe down the surface with a dewaxer. Wax removal is critical. Do not use acetone as it flashes too quickly and does not remove all the surface contaminants. If any silicone polishes (Star Brite, etc.) have ever been applied, be sure the solvent is blended to remove silicone. Use the remover generously so that you wipe the residue off and not just smear it around. Apply the dewaxer using a two-rag method: one rag to apply and one rag to remove.You will need plenty of clean rags and must change your rag often. Wiping a 2' x 2' section at a time is the best approach. Rotate the pad often to expose fresh cloth. A double de-waxing would not be overkill. Last, wash the area well with a strong detergent, including TSP (Tri-sodium-phosphate). Any good paint store should have it. This will help degrease the surface.
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2. Fill any dents or gouges.
Fill any gouges with an epoxy fairing compound and follow with sanding. Let the putty stand "proud" above the surrounding surface so that it can be faired and smoothed by sanding. Epoxy filler is tough, so power sanding with a variable-speed, random-orbital sander is recommended. Rough sand the patch with 60 grit before switching to 120 grit to get the final contour.
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3. Sand and prime.
Topside paints can be used on any surface (wood, metal, epoxy, Gelcoat) as long as the surface is prepared properly. If your boat has previously been painted and you are unsure if it was done with a two-part or single-part paint, use a single-part. Two-part paints are not compatible with single-part paints.
Preparing Wood (Unpainted)
Fasteners in wood hulls are always countersunk below the surface of the wood. It is necessary to fill these countersinks in order to achieve a completely smooth finish. The countersinks should be filled with plugs. Do not use epoxy or polyester putties for this job, precisely because they bond so well to wood. (Webmaster's note: This is a matter of opinion.) Should it ever become necessary to remove the wood for repair, it would be difficult to get to the fasteners under epoxy putty.
Bare wood should be sanded smooth with 80-grit paper before application of a filler type primer. The purpose of this primer is to fill in the grain of the wood. It has an unusually high amount of solid material. Allow the primer to dry for 24 hours before sanding with 220-grit paper. The goal is to sand to the thinnest possible paint film without sanding down to bare wood. Obviously, this cannot be done with just one application of primer. Some bare wood will inevitably show and require a second or third coat and sanding. Primer coats and sanding should be continued until the grain is completely filled and the surface is smooth.
Carvel planked boats require seam compound. Traditional seam compounds are never applied until after the hull has received its primer coat. They should never be applied to bare wood. The exact opposite is true of polysulfide seam compounds that must be applied only to bare wood. When polysulfide is used, it is put into the seam prior to applying the primer.
Preparing Wood (Previously Painted)
Paint in good condition should be sanded with 220-grit paper to knock off the gloss. Use a random orbital sander. This will invariably reveal some paint that is blistered or flaking and which needs to be scraped off the hull. In these spots, it may be necessary to sand down to bare wood. Such areas should receive a coat of filler type primer and be hand sanded to "feather" them into the rest of the existing paint.
Paint that has been sadly neglected must be completely removed. Power sanding is the only way. (Webmaster's note: Not true. If the paint is not a two-part urethane, it can be removed with a heat gun.) Paint remover is too costly and too time consuming. This process is affectionately known as "wooding". Once the old paint is gone, prepare the hull as if it were new bare wood.
Fiberglass gel coat is not an ideal surface for paint. It is so slick and has such low porosity that paint has a hard time adhering. A primer coat that chemically softens the gel coat and bonds to it should be used prior to applying the first finish coat of paint. Special fiberglass primers are made just for this purpose.
According to International Paint (Interlux), the use of this type of primer results in better adhesion of the finish coat than can be obtained by sanding the gel coat with 80-grit paper. Always choose a primer that is compatible with the finish coat paint. If sanding is chosen instead of a primer coat, the goal should be to remove all gloss and establish a good anchor pattern for the paint.
Primer can be applied with a brush or a roller. Using a roller speeds up the work and provides a more even film thickness.Do not worry too much about looks at this point. Just be sure that the entire surface is given a thin even coat with no skips. To understand how a fiberglass primer works, think of flypaper that is sticky on both sides. The primer softens and bonds to the gel coat on one side. On the other, it provides a chemically compatible base for the first coat of finish paint. Professionals often refer to this type of primer as a "tie coat". The chemical bonding to the finish paint works best when the primer is still quite fresh.
Apply two coats of epoxy primer, sanding in between coats. The next step is to sand the entire surface with 220-grit sandpaper, depending on the hardness of the surface. When power sanding, a variable-speed random orbital sander with a circular foam pad works best. Hold the sander perfectly flush on the surface or you will create dips and swirl marks. Avoid the temptation of tilting the sander from the flat position when sanding areas where filler was used.
When hand sanding, always use a sanding block (rigid or foam) to ensure that you do not add any dips in the surface that may appear in the finished surface.The next day wet sand the entire area with 220-grit paper and lots of water. Then do a thorough water wash and a full wipe down with thinner, rotating and throwing out the rags every couple of feet. Then paint it again. Be sure not to touch the surface after cleaning or you will spread contaminants that can affect the cure.
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Do not use 3M fine line masking tape, unless you like retaping every day; while a terrific product, it is not designed to stay on for more than a day or two and will leave residue if left on longer, especially outside. In addition, the thin tape may be more difficult to remove with a thick Awlgrip on top of it. Use 3M #225 tape it works flawlessly and removal is easy with no residue even after more than 3 weeks on the boat.
It is no longer possible for do-it-yourself application of many two-part urethanes popular for refinishing fiberglass boats. These paints use isocyanates and other dangerous chemicals in their formulations. Under current OSHA and EPA regulations, they can only be sprayed by professionals using supplied-air respirators. Less durable formulae are available for most two-part urethanes. These do not use the regulated chemicals, so can be used for do-it-yourself application. Even so, chemical respirator masks, protective clothing and eyewear are essential. Many people prefer to use the single part polyurethane. The two part gives a harder more durable finish. However, you have to mix the two parts and fiddle with the ratio to get it to be runny enough to level itself out, but not so thin it runs.
Unless you are an expert with spray equipment, the best way to apply paint is the "roll and tip" method. One person rolls a thin coat of paint. The second person follows the roller with a brush. The brush removes the "stipple" created by the roller and produces the smooth finish.
Rolling paint is the best way to get the desired great gloss thin finish coat. Use a solvent resistant (phenolic core), high density/closed cell foam roller with a 1/8" nap. This will minimize the formation of bubbles in the surface that can occur with mohair and large cell foam rollers. A thick coat with a regular roller will run or sag and may not adhere as well to the substrate.
One word of caution: check that both the roller covers and the brushes you plan to use are compatible with the paint before your start the job. Many brushes and roller covers will fall apart in the solvents used with these paints.
Bigger is not better. A 9-inch roller loaded up really has enough paint on it for two or three, 3 square foot sections. If you roll more than 3 square feet at a time and then try to spread the excess paint, the paint will already be setting by the time you start tipping and the brush will drag and leave marks. You will get too much paint on the first section, just right in the second, and not enough in the third.
A good approach is to roll the paint on in about a 2' x 2' square area. Roll out the paint in a big W and then re-roll the area to distribute all the paint evenly in the 2 foot square area. Roll horizontally, then tip vertically with a good unloaded 3" bristle brush.
It takes a certain amount of trial and error to get the knack. Too much paint and it will run. Too little and the roller marks will not tip out or the brush will drag and leave brush stroke marks that do not level out. The proper amount of reducer is critical, and you will likely have to add more as you go along. If the brush drags even a little, add more reducer (in small increments).
Paint runs are a problem when rolling vertically then tipping horizontally. Instead roll horizontally and then tip vertically top to bottom. Then the last motion that touches the paint is downward and excess paint will be pulled down off the side of the boat to the bottom. The paint then levels out horizontally resulting in no roller marks, no runs, and no brush marks.
Clean the tipping brush with solvent every single time it is used. This keeps the brush from loading up and brush strokes in the paint unbelievably fine, hence they flow out and level as the paint sets.
You need to work and move quickly. If you move too slowly, the paint will already be setting and the brush strokes do not level out.
The next day wet sand the entire area with 220-grit paper and lots of water. Then do a thorough water wash followed by a full wipe down with thinner, rotating and throwing out the rags every couple of feet. Then paint it again.
Do two to three coats this way. You should find that with your nose 12 inches or less from the hull and the light at ANY angle there are not but a handful of tiny brush strokes to be seen, much less roller marks. The very small number of imperfections that sneak in are not visible from two or three feet away.
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