Sand, Blast, or Strip Your Way to a Smooth Bottom
Before taking on a giant paint project, study methods, precautions, and costs. From our February 2008 issue "Hands-on Sailor"
Few maintenance jobs are as potentially gruesome as removing your boat's bottom paint. Ordinarily, this odious job comes up after about 20 years of nonablative-paint residues have built up below the waterline. But other factors, including gel-coat blister prevention, better boat speed, a pre-purchase survey inspection, or the adjustment of your boat's waterline, can also prompt a full-tilt bottom job.
Whatever the inspiration, it's important to approach this job with personal safety in mind, in addition to employing methods that allow you to work quickly and efficiently. There are also significant environmental considerations to weigh, especially where local laws mandate the mitigation of toxic hazards. And, of course, cost and convenience come into play, too. So it's best to start by answering the single most important question: Is this job necessary?
Without question, bottom-paint removal is necessary if you know that your boat has gel-coat blistering below the waterline. If left untended, these blisters typically expand and eventually compromise not only boat speed but hull integrity. Once discovered, they have to be addressed and preventive measures taken before the hull is repainted. (More on this in next month's CW.)
Less certain, at least on a cruising sailboat, is whether you need to remove old bottom paint to improve boat speed. Old paint does indeed add weight to your boat, but even 20 years' worth of residue adds only a marginal amount of poundage to the boat's overall weight. More likely, old bottom paint will result in an uneven surface, which increases drag as the boat moves through the water. But calculating the toll of imperfections and weight is dicey at best, and it may be of marginal importance to a long-distance cruiser. In short, how much labor and money do you want to invest to gain, say, a quarter of a knot of boat speed? For racers, the answer's easy: Take off the old bottom paint; toil and cost be damned. For some cruisers, however, a quarter of a knot may not be worth the effort and expense.
At least the partial removal of old bottom paint may be necessary in two common situations: when you or a marine surveyor are conducting a thorough pre-purchase survey, and if your boat's kept idle for long periods in warm, southern waters, where it's a good candidate to develop small blisters that hide under bottom paint. Because blistering is more common in warm-water boats, partial random removal of bottom paint may be advisable on a routine basis.
Some bottom paint may also need to be removed when a part-time cruiser becomes a liveaboard. All the extra gear, stores, and tankage can raise a boat's waterline, necessitating the scribing of a new boot stripe and the addition of some bottom paint.
In any case, be forewarned: Once you start peeling away old paint, you may conclude that complete removal makes sense. It's the old "I've come this far, I may as well finish the job" syndrome. And that's when you have to ask yourself, "Do I want to do the job, or should I pay to have it done?"
Hiring a professional to do the dirty work is more expensive, but personal health concerns and complex environmental issues are eliminated when you bring in a pro.
Three removal methods dominate the bottom-paint scene these days: soda blasting, chemical stripping, and mechanical sanding. Wooden-boat owners have the added option of using heat to remove old bottom paint, while aluminum or steel hulls can stand up to sandblasting. In all cases, though, safety precautions are critical because dried bottom paint is a toxic, hazardous material.
If you're going to do the work yourself, you'll want to suit up before you begin. With any of these removal methods, gloves and safety glasses are mandatory. When soda blasting, sandblasting or sanding, a disposable jumpsuit and a high-quality dust mask are also essential. And when taking off paint with a heat gun, upgrade the dust mask to an organic-vapor respirator.
Soda blasting, rapidly becoming today's removal method of choice, is a significant upgrade from ordinary sandblasting. On fiberglass boats, sandblasting leaves the underlying gel-coat surface badly pitted, while soda blasting leaves it unscathed. The "soda" in this method is made up of larger crystals of plain old baking soda, which helps reduce environmental hazards.
Although it's possible to do soda blasting yourself, most boat owners hire the work out, which costs between $40 and $65 a foot. The higher rate is generally applied to boats larger than 45 feet, which have a greater beam and, therefore, more surface area. Higher rates are also found in states in which environmental laws force contractors to follow expensive cleanup and disposal procedures. By renting a soda-blasting machine, you may be able cut the cost of the job nearly in half. But this is fairly labor-intensive work, rental units are scarce, and you still must dispose of the old paint properly.
Rather than using soda blasting or sanding, many marinas prefer to chemically remove bottom paint. The chief advantage in chemical stripping is better control over environmental hazards, particularly toxic dust and noise. Chemical stripping is also the simplest of stripping methods, requiring skill with only a paintbrush and a scraper-provided that you strictly adhere to the manufacturer's instructions. When done by a professional, expect chemical-stripping costs to be in the same neighborhood as soda blasting, usually between $45 and $75 per foot. Again, costs may run higher in states with stricter environmental laws.
For the do-it-yourself boat owner, chemical stripping has some hazards to weigh against its ease of use. First, be sure to get a marine stripper that doesn't contain methylene chloride, and be sure that it's compatible with use on fiberglass. Until about 10 years ago, methylene chloride was a common ingredient in nearly all chemical strippers. It is, however, widely regarded as a carcinogen. Moreover, as it emulsifies old finishes, it gives off carbon monoxide. Fortunately, most marine strippers today contain no methylene chloride. But many still contain highly toxic chemicals, including acetone, toluene, and ketones, so working in an environment that has plenty of fresh air is essential.
But that environment usually can't be your backyard or the local boatyard. Most chemical strippers are very sensitive to direct sunlight. Moreover, chemical strippers work best when both the boat's hull and the ambient air temperature is around 70 F. Much higher or lower temperatures can seriously compromise results. And, of course, stripped paint containing chemical-stripping residue is a toxic waste and must be dealt with as required by local environmental regulations. Chemical strippers are pretty expensive, too, costing between $50 and $125 per gallon. To strip the average 30-foot, full-keel sailboat requires about five gallons of stripper, depending on how thick the paint is.
Least expensive of all is sanding off old bottom paint. Many boatyards won't use this method anymore because it's messy, and it makes complying with local environmental mandates very difficult. If you can find a yard that will strip your boat's bottom paint via sanding, the cost generally will be in the neighborhood of $50 per foot. Most of that expense is in the labor.
Meanwhile, for do-it-yourselfers, sanding off bottom paint is a toilsome, although fairly inexpensive, job. With an investment in about $60 worth of 80-grit sanding discs and a six-inch random-orbit sander that will set you back about $100, you can remove all the bottom paint from the average 30-foot sailboat in about 15 to 20 hours. The odious nature of the job comes in three parts. First, you must cover up to keep the toxic sanding dust off your skin. In the past, I've found disposable jumpsuits and a head sock ($10 each) to be ideal. Regular clothes will get so filled with dust that they'll be rendered unwearable. Goggles, a tight-fitting dust mask, and heavy-duty gloves are also a must. And shoulders, arms, and hands of steel are a good idea, too.
Although standards vary from state to state, all methods of bottom-paint removal dictate at the very least some common-sense precautions. First, plan to corral as much of the removed paint as possible. This means having a drop cloth covering the ground under the boat. For soda blasting or sanding, it will also be important to "tent" the boat's bottom by hanging plastic sheets from just above the waterline to the ground; have them reach all the way around the boat. Otherwise, the dust will fly everywhere.
Regardless of which stripping method you choose, old paint or stripper residues will require proper disposal. Again, the exact disposal procedure varies from state to state. Where regulations are most stringent, the removed paint may have to be separated from the removal medium, the baking soda or the chemical stripper. The separation process requires special equipment not available to the do-it-yourself boat owner. To comply with regulations, you'll have to find a local company specializing in hazardous waste, which can usually be tracked down through your household trash hauler. Fees for hazardous waste disposal can run between $100 and $200.
Unless you're working in an enclosed (but well-ventilated) area, some other environmental precautions will also be necessary. First, never work in breezy conditions. When sanding or blasting, toxic dust will escape even a well-tented boat and land on other boats. And few chemical strippers work well with a breeze drying them out faster than they can act on the paint. Also, be sure the ground cloth under the boat offers some measure of traction and water permeability. Fine dust on top of plastic sheeting is surprisingly slippery. Moreover, most stripping methods conclude with washing the hull with water; the runoff must be able to pass through the ground cloth in addition to leaving residual sanding dust and removal medium behind. Professionals use a feltlike carpeting to comply with regulations and to separate water from residues.
Given the cost and work involved, it's easy to see why some cruisers are willing to sail a little slower on a less-than-perfect bottom. Still, for those who decide to spend the money, time, or both to do the job right, the reward will be a smooth hull sliding into the water come launch day.
Ken Textor is a frequent CW contributor. Next month, he writes about blisters and barrier coats to protect that newly cleaned bottom.