Along with changing the engine oil, stripping multiple layers of old bottom paint has to be one of the most onerous jobs a boat owner faces. If youve got a lot of bottom paint, to the point that it has begun flaking off, it is time to take the bottom down to gelcoat.
Since methylene chloride, the active ingredient in many strippers, was determined to be carcinogenic, chemical companies have been working to develop safer alternatives. Weve been testing these so-called safe strippers for several years.
The active ingredients used in these new products include acetone, methyl ethyl ketone (MEK), toluene, dimer acid, hydroxyethanoic acid, dibasic ester and methyl-2-pyrrolidone. Most of the labels call these products environmentally friendly and biodegradable, but also warn that they cannot be made non-poisonous, adding that they may be fatal if ingested. Clearly, these are still powerful chemicals. After all, they have to emulsify paint or penetrate and release it from the substrate-no mean feat.
Why Use a Stripper?
Good question! This most recent test reminded us what a messy job it is, especially working on an overhanging surface (i.e., the bottom of a hull). While some of the products can be sprayed (one, Napier SV-35/M insists on professional spraying), most owners will use a brush for application. Thats what we did. The five strippers tested all have the consistency of a thick gel or paste, and instructions call for laying it on as thick as possible. The stuff invariably slops off onto the ground, your arm, your face… It aint clean and it sure aint fun.
And because this stuff isn’t cheap-up to $200 per 5-gallon pail-you hate to see an appreciable portion of your investment falling off, wasted. (Oh, be sure to spread a drop cloth or cheap plastic cover on the ground to catch the slop and the bottom paint scrapings which will follow.) After applying the stripper and waiting the recommended time, you then have to scrape off what paint will come. Most likely, youll have to apply a second coat of stripper and scrape again. Then, with any luck, you will sand the bottom (we like a random orbit sander) and be done with it. This might be a good time to consider applying a barrier coat.
But what are the alternatives? Shotblasting is an option but not inexpensive. And there is the risk of damage to the gelcoat. Operator proficiency is key.
Several years ago, we reported on the Armex Accustrip System, which is essentially shot blasting with baking soda as a media. Its about as fine as talcum powder. The idea is that it is less abrasive and less likely to damage the gelcoat. Developed by Church & Dwight Co., makers of Arm & Hammer baking soda, Armex is used for removing grease, rust, paint and other coatings from industrial equipment. Accustrip is the name of the blasting apparatus.
As we discovered in our test, it works well, but anything that can take paint off, can damage gelcoat, too. It depends on the amount of pressure used, and the operators skill. Following our report, one PS reader reported watching a boat being blasted with Armex; all went well until the operator failed to recognize the gelcoat, and cut through it to the underlying laminate. The owner stopped him when he realized his gelcoat was being taken off.
Cost is 57-1/2 per pound. Expect operators to use about a half pound per minute at 20 lbs. pressure. Because the baking soda media is so fine, it wont work in ordinary blast equipment typically owned by boat yards. The blasting is most often done by contractors with mobile trucks. Last time we checked, technicians worked for $125 per hour. We were told it would take four hours to do a 33-foot boat-total cost: $500-$600.
The bottom line with shotblasting is to watch the job carefully and not hesitate to stop the process if you believe your gelcoat is being damaged.
Another reader said a good shotblasting job leaves just a little tooth for good paint adhesion. Any more tooth than that and you may find yourself having to fill and fair the bottom by troweling on epoxy and some sort of filler. That means a lot of work, both in application and in sanding.
It is possible to scrape the paint off with a good quality scraper. Occasional contributor Bill Seifert says he can clean the bottom of a 50-footer in one day with a 1 Red Devil scraper. We don’t doubt him, and maybe this is ultimately easier, but we don’t aim to find out. Scraping may be worth at least an experiment. If the paint sheds easily with one pass, perhaps youll go for it. But if it resists, as do the two oldest layers of bottom paint on Viva, our 1975 Tartan 44 test boat, wed resort to sanding at that point. In any case, round the corners of the scraper so as not to gouge the hull, and keep a file handy for frequent sharpening.
Which brings us back to the strippers. Cost to do a 40-foot boat yourself may well be upwards of $500, especially if you require two coats. Still, this is a significant savings over a professional shotblasting. But youll pay the difference in sweat and hard labor.
There is no easy way to remove multiple paint layers; either you do the work, or pay someone else to do it for you.
The Tests
In addition to perennial winner Peel Away, the four other products tested this year were Dolphinite Marine Paint and Varnish Remover, Interlux Interstrip 299E, Napier SV-35/M and West Marine MarineStrip Bottom Paint Stripper System.
Peel Away and West Marine MarineStrip are brown-colored pastes. The others are opaque or colored gels. All were applied with a disposable brush, though as mentioned, some can be sprayed.
Sections of Vivas hull were taped off into about 2′ x 5′ rectangles. These in turn were taped into smaller sections. Each stripper was applied to the squares within its rectangle. After 30 minutes, we scraped the first section in each rectangle and noted the results. Subsequent sections were scraped at 1 hour, 2 hours and at the maximum time duration specified for each product, which varied from 3 to 36 hours.
The Results
None of the products did much in the first 30 minutes. After one hour some paint was removable and after two hours a bit more. The results are noted in the accompanying chart.
Some of the strippers began to harden after about four hours, making removal of the dried-out gel difficult. Some of the strippers call for specific cleaners to remove, such as Interstrip 399 for Interstrip 299E, Peel Away All Purpose Cleaner and Surface Prep or mineral spirits for Peel Away. They will, however, sand, but not always easily. Better to scrape away the stuff before it hardens and save the step and cost of an extra product.
All of the strippers removed the three to four layers of black bottom paint on top, but not uniformly. None of the strippers penetrated the well-adhered blue and green bottom layers. A second application was required to get to gelcoat.
We found that Peel Away and West Marine MarineStrip were the most effective, with Peel Away having the decided edge. Part of the reason we believe is that Peel Away is by far the thickest paste and least likely to drip off. Both of these products require that you plaster a cellophane sheet (provided) over the product to keep the solvents from flashing off. This keeps the paste from drying out and allows it to remain active longer. The other three do not provide a plastic film, nor would you want to with Dolphinite or Interstrip 299E as they should only be left on the hull a few hours and will still be moist at the end of that time.
After 24 hours, the Peel Away was still wet and active while the West Marine stripper had unexpectedly hardened under the plastic sheet.
Because Peel Away removed the most paint and was the easiest to apply, it remains our winner. West Marine MarineStrip is second, but test it periodically to make sure it isn’t hardening. Dolphinite, Interstrip 299E and Napier SV-35/M performed more or less the same, with the advantage going to the first two. Napier believes that if we had sprayed its product, as recommended, it would have performed better.
Performance varies with ambient temperature and most stripper labels stipulate a minimum such as 50F. In our experience, and from what weve learned from other users, its much better to apply in temperatures of at least 65F and higher. Our test was conducted in 75F weather.
Gelcoat Damage?
Just as we were beginning these tests, we noticed the owner of a neighboring boat using Peel Away on his newly purchased Nordic 44. The bottom required two applications, and we winced as we watched him slather the paste onto the boats big bottom. He had the stuff slopped all over him. When at last he finished, we (and he, we guess) were horrified to see that perhaps 20% of the bottom had no gelcoat.
Our first thought was that the gelcoat had been damaged earlier and hidden by bottom paint. What a sad surprise for the new owner!
At this same time, we were testing yet a sixth stripper-MDRs Strip Away-sent to us by the company in response to a PS Advisor about removing cured varnish from non-skid fiberglass decks. The Strip Away didnt work on Cetol (which splatters horribly), but was somewhat effective on cured varnish. It didnt appear to harm the gelcoat but when we noticed some bare spots a few days later, we got nervous.
This got us to thinking again about our neighbors Nordic 44 problem. Next time we saw him, we asked if the Peel Away had possibly eaten his gelcoat. No, I don’t think so, he said. He figured it had been damaged earlier and simply painted over. But I had some areas where the Peel Away had a tough time removing the paint, so I got some real nasty stuff and that did appear to damage the gelcoat, he said.
By now we were leery about what all strippers do to gelcoat.
Checking Vivas hull again, we were disturbed to see that most of the strippers had continued penetrating the paint even after a liberal water rinse at the end of the test.
Marine surveyor Tony Knowles of Newport Marine Survey Group was asked to inspect the hull. He confirmed that in several places the gelcoat had been penetrated. Again, we were thankful not to have treated the entire hull. The damage was limited to areas no larger than a dollar bill and were not deemed serious.
Back at the office, we obtained a two- or three-year-old hatch cover, marked it off with tape, and applied all six strippers-the five tested on Vivas bottom plus MDRs Strip Away. Interlux Pintoff 199, containing methylene chloride, also was tested, just for the hell of it. Again we checked at intervals. Only Dolphinite, Interstrip 299E and Napier warned about possible gelcoat damage. Dolphinite said not to leave it on longer than 4 hours, Interstrip no longer than 8 hours. Napier gives more specific warnings about soft gelcoat of less than 30 in the Barcol hardness test, adding that SV-35/M may not be appropriate for all hulls.
After 1 hour, Pintoff began to raise the gelcoat ever so slightly, visible only in a reflected light. After 4 hours, Interstrip 299E, Napier and Dolphinite did the same.
After 1-1/2 hours, Pintoff destroyed the gelcoat, cracking and lifting it into dime-size fragments that looked like a dried, cracked mud flat.
After 24 hours, Dolphinite did the same number on the gelcoat and after 48 hours, Interstrip followed. After about 60 hours, Napier cracked through, too.
Peel Away, West Marine MarineStrip and Strip Away neither lifted nor cracked the gelcoat. Both Peel Away and West Marine MarineStrip note, however, that the potential for gelcoat damage exists and that tests on small patches should be conducted prior to application of the entire hull. New gelcoat is much more resistant to damage from paint strippers than old, porous gelcoat.
This test was somewhat unrealistic in that the strippers were placed on bare gelcoat, with no paint, and left far longer than instructions recommend. Then again, it is evident that the longer you leave a stripper on, the better it works. But don’t be fooled into exceeding recommended time limits, because even if you have rinsed the hull or neutralized the stripper with the recommended treatment, it is possible that some of the stripper, absorbed in the paint, resisted neutralization and continues to eat away. The damage wont necessarily be visible until all paint is removed.
We obtained a copy of a test done by the Dockyard Laboratory Pacific (DLP) in Victoria, British Columbia, a government agency. DLP tested Peel Away Marine Strip II (a different product than we tested and intended for boats with barrier coats or very aged gelcoat), Napier SV-35/M and Interstrip 299E for possible damage to gelcoat. Gelcoat weight and hardness were measured as well as examination for chemical changes using Raman spectroscopy and mechanical tests for changes in modulus, strength and flexibility. As in our test, the three products were applied to bare gelcoat that had been aged in a weather chamber.
Results indicate that all of the gelcoats were softened, but over time recovered much of their hardness, though not the same for each product. Interstrip 299E was absorbed the most and the gelcoat only regained half its original hardness. Peel Away Marine Strip II absorbed the least but showed significant surface attack, including discoloration and permanent loss of weight. Napier SV-35/M was the least harsh, showing no permanent loss in hardness of more than 10%.
Our best recommendation is not to leave any stripper on bare gelcoat any longer than necessary.
Recommendations
In our test, done in warm weather, most of the strippers seem to have done the majority of their work within 4 hours. Test often to see when you can start scraping.
Adhere to the manufacturers recommended maximum exposure limits. Exceeding these may cause gelcoat damage.
Neutralize the stripper per manufacturers recommendations, but beware that stripper absorbed in the paint may continue to work. Finish scraping in a timely manner (not next day) so that absorbed stripper is removed, and to avoid the problems of sanding/cleaning hardened stripper.
Of the five products tested, Peel Away Marine Safety Strip remains our preferred bottom paint stripper because it is the thickest and therefore easiest to apply. It remains active longest. West Marine MarineStrip, which also uses a plastic film, seemed to work as well as Peel Away after four hours, but hardened overnight.
Interstrip 299E, Napier 35-SV/M and Dolphinite all seemed to work more or less equally. Napier is only available by professional application, so do-it-yourselfers are limited to the others. Interstrip and Dolphinite would be good for small jobs. Both of these are potentially damaging to gelcoat, so be sure to remove and neutralize within the recommended time period.
Contacts- Armex & Accustrip, in the Northeast, Dawson-McDonald, 845 Woburn St., Wilmington, MA 01887; 978/988-8034. For other distributor names, US Filter/Schmidt, 800/231-2085. Dolphinite, 43 Water St., Box 12, Beverly, MA 01915; 978/232-0150. Interstrip 299E, Interlux Yacht Finishes, 2270 Morris Ave., Union, NJ 07083; 800/468-7589. Napier International Technologies, 9439-192 Street, Surrey, British Columbia, Canada V4N 3R7; 800/564-9929. Peel Away Marine Safety Strip and Marine Strip II, Dumond Chemicals, 501 Broadway, New York, NY 10036; 212/869-6350. Strip Away, Marine Development & Research Corp., 2116 Merrick Ave., Suite 4001, Merrick, NY 11566; 516/546-1162. West Marine, PO Box 50070, Watsonville, CA 95077-0070; 800/262-8464.
