Gelcoat Repair Kits: Bondo Best
In the beginning, there was paint, and for a long time the repair of scratches and gouges was relatively simple.
Today, we have gelcoat, in which cracks, chips, and scratches are a constant problem for owners who want to keep their vessels looking good. Gouges must be filled and faired smooth. Cracks need to be opened (routed out) and similarly filled and resurfaced. Like bodywork on a car, gelcoat repair is as much art as technology.
We wanted to see what’s involved and how difficult it is for average boat owners to do their own gelcoat repair using the available "off the shelf" products. We visited the BoatUS, West Marine, and Overton’s websites and ordered the three most common gelcoat repair kits available—from Evercoat, SeaFit, and Bondo. We reviewed and closely followed the instructions that were included, and we also put the kits through a few unanticipated paces that an owner might encounter.
What We Looked At
We began by taking an inventory of what each kit includes. We then evaluated the quality of the instructions by reviewing them for clarity, detail, accuracy, and the availability of technical support. We looked closely at the gelcoat base resin materials to determine ease of mixing, color change from curing, and exothermic heat generation. We then assessed the mixed (combined) system for working time, sag resistance, cure time, ease of handling, ease of sanding, fairing, and compounding, and final gloss and hide characteristics. As a final test, we subjected the repaired surfaces to a two-week-long UV exposure to look at the color stability of the repairs.
All the kits contained what their suppliers refer to as their resin or gel base. We began by using the base resins in an unmodified fashion with no pigmentation. All suppliers required the use of teaspoon or tablespoon quantities for metering the base resin. None included a measuring device in their kits.
Working time is very important with these types of materials since their mixing and application must be complete prior to the materials thickening to what is called a gel point (the point at which the material begins to thicken like gelatin).
All the instruction sets estimated working times for the catalyzed base at room temperature. The catalyst supplied by all the kit makers consisted of MEKP, which is a clear liquid supplied in a tube. All MEKP tubes were sealed and had to be cut open for use. No instructions for opening the tubes were included. This procedure might seem obvious, except that all instruction sets referred to metering the catalyst in terms of drops of catalyst per teaspoon or tablespoon of base resin, and depending on how the tubes are opened, drop size variations can be fairly large.
With respect to the use of the pigments, no instruction as to the amount to be used was included except for a maximum quantity not to be exceeded. The Evercoat and SeaFit kits advised using the pigments sparingly.
To look at the accuracy of the combination and mixing information, we first measured the teaspoon weight of the base. We then measured the weight of the catalyst drop quantities given in the instructions. Although both teaspoon and tablespoon quantities were given, they were not identified as level, heaping, or anything in between. A level teaspoon weighed about 5.0 grams and an unleveled teaspoon could weigh as much as 11.25 grams. The catalyst/resin ratios and their effect on the final color can have a big impact on your success and the longevity of the repair.
We looked at the ability of the mixed repair materials to hang on a vertical surface between the temperatures of 65 F and 95 F, since that range represents real world conditions. Hang was checked by filling both a gouge and a deep scratch with mixed repair material on a piece of gelcoated laminate that was pre-heated to the test temperature in a Fisher Isotemp oven. The panels were then held vertically and horizontally (upside down) until cured. The initial and final positions of the repair materials were recorded.
Note to the kit user: A white hull in the high summer sun can reach 160°F and a dark colored hull over 200°F. Don’t try to make this type of repair in direct sunlight if working time and the hang-ability of the repair is a consideration.
We measured the gel times, exotherm and working times of the mixed systems by combining 10 grams of material and catalyzing at the recommended catalyst drop ratio provided in the instructions. We assumed that the instruction writers meant a teaspoon was a level teaspoon.
We cut our catalyst tubes open by piercing their tops with the point of a standard utility knife blade. Both the SeaFit and Evercoat kits called for 4 drops of catalyst per teaspoon of mixed material. The Bondo kit called for slightly more catalyst at 5 drops per teaspoon or 10 drops per tablespoon. Unfortunately, if any more than a level spoon unit measurement was used, the catalyst ratios dropped into ranges that would be considered low, especially in cold weather (65°F). Cure of thin or small-mass areas of these materials at low catalyst ratios would result in slow and possibly incomplete cures of the patch material. This would compromise their color stability and weather resistance.
We prepared a plaque of white gelcoated laminate with both a deep scratch and a wide gouge (down to the fiberglass surface). The gelcoat on the plaque was Cook Composites and Polymers' Armorcoat standard white (a leading NPG isophthalic incorporating modern technology to inhibit UV color change and provide increased toughness). Following the manufacturer's instructions to the letter, we mixed and filled both the scratch and the gouge using the items supplied in the kits.
Neither the Evercoat and SeaFit kits provided any materials to be used in the finishing process after the patches had cured. Their instructions included only one line mentioning the use of 600-grit wet sand and polishing compound to complete the job professionally. The Bondo kit dealt with the subject of finishing more extensively and provided materials for finishing as well.
During repair we noted the handling characteristics of each kit with regard to tools and materials. All our repairs were made at 75°F in an environment with controlled humidity.
What We Found
Kit contents: The Bondo repair kit at $29.99 was the most expensive kit in the group. However, it contained all that’s required to do the job from mixing to finishing except the final wax and buff materials. It included a significantly greater amount of resin gel base, pigments and catalyst (8 fluid oz. compared to 3 in the large SeaFit and Evercoat kits), as well as two different grits of sandpaper (one coarse dry and one fine wet) and some fine polishing compound. It had more basic tools for mixing and dispensing the repair material, as well as two sheets of plastic release film instead of one in the other kits.
Given the fact that a larger percentage of boats are white than any other color, half of the Bondo base resin (4 oz.) was pre-tinted white. Bondo recommended this for light colored gelcoats as well.
The large Evercoat and SeaFit kits cost in the range of $19.99 to $21.99 but provided less than half the total repair material and no materials for finishing the repair.
Bondo only offers the large kit, while both SeaFit and Evercoat sell smaller kit versions that cost about $15.99. They consist of 1 oz. of resin base and the same number and quantity of pigments and catalyst as in the larger kits, but no release film or mixing cups and less detailed instructions (on the back of the package).
Evercoat also sells a separate 6 oz. can of the resin base (gel paste) for $12.99 and separate pigment colors for $5.99 each (larger tubes). If you have future repairs and don’t think you need all the elements of the kit, this might be a better option to consider, especially if you know what tints you want and how to match them, or have a large repair area.
Both the SeaFit and Evercoat kits also contained a small tube of cleaning solvent, while Bondo did not.
Instructions: The Bondo instructions were, by far, the best in the group. They wisely recommend that you mix and cure a test quantity of patch material and check it against the original. This helps you adjust for any color shifts due to base resin or catalyst amount. They also suggest taking the color match test material from a larger quantity of mixed material. If the cured material looks good, the rest of the retained material can be used or slightly adjusted.
The Bondo instructions also lead the user through the finishing steps, as well as provide considerations for different types of repairs such as scratches vs. holes or larger impact areas. Bondo provided an assistance number for questions related to their kit. Our call was returned within 30 minutes by a professional who had extensive hands-on experience with the products and repair types. We also called the Evercoat tech help line and received an answering machine. An equally experienced person in this area returned our call after 5 hours.
The SeaFit kit contained no type of contact information for technical questions or problems.
The SeaFit and Evercoat instructions were nearly exactly the same, as were the contents of their kits. Based on the help line in the Evercoat instructions we would guess that Evercoat sells their kit contents to West Marine, which in turn uses its own packaging and slightly different instructional format, and sells the kit under the SeaFit label.
We feel that both Evercoat’s and SeaFit’s instructions are weak in most areas, particularly with respect to color matching. This is an extensively complicated area and difficult for most to execute. Possibly for that reason, all the instruction sets tend to treat color matching in a cursory way, leaving the real work up to the user.
We were surprised that neither the SeaFit nor the Evercoat instructions required pre-sanding the repair area before application of the mixed patch materials. This is important when considering how well the patch will adhere to the original gelcoat. Their instructions simply said to wash the area with the solvent provided, a weakened version of acetone.
Based on our experience, surface preparation is the most important part of the repair process. On any flat areas outside the scratch or gouge where both the SeaFit and Evercoat patches were applied to unsanded gelcoat, the patch was easily separated. It was also difficult to feather the edge of the repair into the original gelcoat due to the lack of adhesion.
It may be that pre-sanding was left out of the instructions because sanding would create a greater need for a focus on finishing—again, a complicated topic, and not one that SeaFit or Evercoat seemed willing to approach.
Mixing and working: Only the Bondo kit cured right on target with the time listed in their instructions. At 75°F, the Bondo product is faster curing, with a working time of about 13 minutes and a gel time of 15. The Bondo product cured solid in 19 minutes in a 10 gram mass (75°F). The SeaFit and Evercoat instructions state a working time of 15 minutes but really offered about 20 minutes of working time at 75°F with a longer gel-to-cure time. This could perhaps be a smart way of assuring ample work time or perhaps off spec material. Both these materials gelled in 22 minutes and cured solid in 27 minutes.
Obviously the Bondo system would offer better working times in cooler weather and the Evercoat and SeaFit systems in hotter weather if these are the normal performance times of the Evercoat and SeaFit systems. At 95°F, the Bondo product's working time dropped to 7 minutes with gelation in 8 minutes. Both the SeaFit and Evercoat working times dropped to 10 minutes with gelation in 11 minutes at the same temperature.
In cooler temperatures (65°F) the Bondo working time was about 24 minutes and the SeaFit and Evercoat materials as long as 45 minutes. All materials cured well at room temperature to yield hard tack-free surfaces.
The Evercoat and SeaFit gel bases were adequately thick at 75°F to hang on a vertical surface. After combining pigments and catalyst, they both ran out of the deep scratch and gouge only a bit. At 95°F neither hung well and would require successive building of thickness to fill a deep, broad gouge.
The Bondo resin base was yet thinner than its competition and after mixing had even more trouble hanging at room temperature. At 95°F the Bondo system drained noticeably out of the deep gouge. All of these results depended on the mix ratio and variation of both catalyst and pigment. The higher the ratio of catalyst and pigment, the more pronounced the hang problem.
With respect to color, the base resin in both the SeaFit and Evercoat kits started out with a light brown tint. The Bondo base had a pink tint. After cure, the SeaFit and Evercoat resin bases turned darker brown. The Bondo resin base managed to hold nearly its original color pink tint after curing. This would tend to make the predictability and matchability of the Bondo colors better than the others. The Bondo product did have a tendency to cure hotter and even crack from heat and shrinkage in larger masses while the SeaFit and Evercoat products cured slower and cooler with no cracking in direct comparison of masses.
All kits recommended the use of a release film to be applied over the repair patch as it cured. Bondo offered this as an optional step to yield a quicker surface cure that could be worked on sooner. Although the Evercoat and SeaFit instructions say the plastic release film will yield a workable surface in one hour, at 65°F it took nearly two hours for this point to arrive. The Bondo product stated two hours and even at 65°F met the stated cure time to yield a workable surface.
We found that generous use of pigment (but below the maximum recommended) was required to yield a repair that was opaque enough to hide the fiberglass surface in the gouge. Our first mixes were too light on pigment and resulted in a see-through effect in the gouge repair.
White is perhaps the easiest color repair to do if you can settle for an approximate match. Many people think that if you can’t detect the difference when you stand away from the hull, it’s good enough. On the other hand, matching a white color precisely is one of the most difficult jobs; the use of other colors for gradations in the tint options requires a surgeon's hand and a way of metering tiny pigment quantities.
Bondo’s provision of a white tint base is useful here, but still requires white pigment to provide complete hide of the exposed underlying fiberglass. Matching other light colors proved very difficult—especially beige, since small tint amounts are required using brown and yellow.
Longevity: All repairs were performed in duplicate. One plaque set was kept in darkness and one plaque was exposed to long-wave UV light for a period of two weeks to assess color stability. The exposed panels were then compared with the dark-room original repairs.
Where white patches were used, the Bondo product was noticeably more colorfast. Both the Evercoat and SeaFit products yielded a slight browning after exposure. When exposed to prolonged heat (160°F) for a period of one week, no change was noted in color, although all repairs yielded a slightly more distorted (sunken) look on the gouge repair surfaces. This indicates that after some time period, your smooth repair area may look slightly distorted and need further fairing application of patch material.
Other Products: There are a couple of other products available in this area, although they are not exactly the types of kits tested here. SeaFit makes a product called Gelcoat Quick Fix at $ 6.99 per unit. This product might be considered for scratches but nothing else. It’s a one-step product in a tube which appears to be based on a solvent evaporation-type system where polymer is dissolved in a solvent and pigmentation added. When the solvent evaporates the polymer and pigmentation is left in place. The dried material is then shaped flat with a sharp plastic tool.
We tried this white Quick Fix in scratches and noted that it worked fairly well, with a couple of exceptions. Its cure is soft and cannot be scraped from an area larger than the width of the scraping tool without removing too much of the patch to yield a level surface. It did show some discoloration in the UV test and offered no options for color adjustment. Future buffing would tend to remove this material from any scratches due to its softness.
There is also a product called Factory Match by Spectrum Color. The product supplied is supposed to be a match to a manufacturer’s original boat color to save the customer the hassle of mixing and matching. Although this may be a good idea for a relatively new boat, the factory color may no longer match a boat a few years old. We didn't test Factory Match.
In all the kits we looked at, there’s a considerable amount of error possible in the final outcome of the repair, due to the lack of clarity in measurement techniques. That said, all three of the large repair kits tested performed fairly well in our semi-skilled hands.
The Bondo kit is the best value for larger or more extensive repairs. It supports a complete repair from gouge to polish with a good wax and buff ending the process. More than twice the quantity of patch material is supplied in the kit. The white tint base is especially useful if you have a white or light colored boat. We liked its faster performing cure and found we could produce a shiny finish much sooner. We also note its better performance in the UV exposure test.
The SeaFit and Evercoat kits consist of almost identical materials, and exhibit almost identical performance. Neither kit addresses finishing the repair, at which point the do-it-yourselfer is on his own. We did not like the dark color shift on the cure of the base resin and noted its color shift towards beige in the UV exposure tests.
If you own a new and expensive boat with a long scratch on its side, or a boat of a non-standard color, you should consider using a professional. If you have an older or middle-aged boat with a moderate number of cumulative cracks, dings and scratches, a repair kit might be just the call.
We recommend the Bondo kit due to its complete contents, good instructions, and the color stability it provides.
Contacts- Bondo, 3700 Atlanta Industrial Pkwy. NW, Atlanta, GA 30331; 800/622-8754; www.bondomarhyde.com. Fiberglass/Evercoat, 6600 Cornell Rd., Cincinnati, OH 45242, 513/489-2602; www.evercoat.com. Spectrum Color, 1410 37th St. NW, Auburn, WA 98001, 800/253-1366; www.spectrumcolor.com. West Marine/SeaFit, P.O. Box 50070, Watsonville, CA 95077-0070, 800/BOATING; www.westmarine.com.
Also With This Article
Click here to view "Value Guide: Gelcoat Repair Kits."