All Aboard Boats: Fix Ation

Repairing fiberglass is a seemingly simple repair that does have a degree of difficulty.

February 11, 2010

All Aboard Boats Fixation

I’m cheating here. Instead of coming up with a fabulously enthralling topic about the how and why of boats, I’m reprinting a reply to one of the many letters you guys send us each month. This question came in from a reader who wanted advice on repairing a small ding in her boat’s fiberglass swim platform. She was also frustrated the she couldn’t get the local glass man to come and fix it. Following is my reply, with annotations in italics. I’m hoping to illuminate two things. First, in describing the repair process, you may discover a thing or two about the properties of fiberglass. Also, while I’m not rah-rahing the marine industry’s reputation for providing service, I think you’ll see a situation that might shed light on the difficulty involved in performing a seemingly simple repair. Out of respect for privacy, no names are mentioned.

You say the ding is about an inch deep? The laminate thickness of most hull bottoms isn’t an inch thick, let alone a swim platform. If you could e-mail a picture, it would allow me to better advise you. Barring that, I’m going to proceed on the assumption that you have a hole through the platform’s fiberglass, and that crushed ’glass makes its appear as though it’s an inch deep. (Your platform is hollow.)

It’s surprising how many people I speak with think they are cruising around on three inches of solid ’glass. Most laminates, properly supported by the stringers, are quite thin, yet stiff and strong enough for the rigors of running through and across the water. It’s when you hit something that you wish you had a “bulletproof” hull. Puncture resistance isn’t built into all thin fiberglass layups , though high-end boats are made using multidirectional fabrics laid up in vinylester or epoxy resin by some iteration of vacuum-bagging (infusion, SCRIMP, etc).


Step 1. Clean out all loose, chipped, shredded fiberglass from the damaged area. Files, rasps and utility knives will all prove helpful for this.

You’re often better off making a bigger hole so that your repair can be affixed to good, solid material, rather than trying to keep the repair as absolutely small as possible. It’s already a hole; get over it. There’s not much more labor and materials in fixing a 4-by-2-inch gash as there is in fixing a 12-by-6-inch gash.

Damage like this requires a pro, but lesser dings CAN be handled on a DIY basis. Courtesy Boat US


Step 2: Use a thin file — or, if you have one, a Fein tool or a Dremel tool — to bevel the edge of the now-clean hole. In other words angle the sides of the hole to a bevel that is four to five times the laminate thickness.

Making ramped edges to an area to be repaired makes it easier to fill the ding because your filler will tend to flow in as you spread it across the hole; with vertical sides, the goop sticks everywhere but the hole. A bevel also gives a greater “purchase” for the patch, making better adhesion.

Step 3: Wipe the area down with acetone.


The boats we enjoy are built and repaired with some really horribly toxic products. You want to wear gloves and a cartridge respirator for this. Acetone is a nasty VOC. Don’t get any on your skin — it goes right through into the blood.

Step 4: You’ll need to apply putty (explained in a minute) to fill the hole. To prevent this from just squishing through into your platform, you’ll need a “backer” of some sort. I’d use a small scrap of wood with a screw attached to its center, sized to fit through the hole lengthwise but wide enough to cover the hole from the backside. Coat the edges of this backer with Super Glue or any quick-setting adhesive. Insert the backer through the hole, rotate it and then pull it against the hole’s perimeter using the screw so that the glued surface contacts the backside of the repair. Hold it until the glue sets.

I know, I know. I could have advised wetting out a little scrap of fiberglass cloth and inserting into the bottom of the hole. Or some chopped strand for that matter. When that cured, it would have sealed the bottom. But then she would have had to WAIT for that, and I figured she was looking to get going. Of course, I also could have described how she would need to wait only until the scrap was “green” cured before applying the filler, but you make decisions in writing like in anything else. There’s more than a few ways to skin this cat. The point is that specialized techniques, including purpose-made tools built on the spot, are part and parcel to working with fiber-reinforced plastic laminates.


Step 5: At this point, you could use one of the pre-made epoxy putty fillers, such as Marine Tex. These are white or gray; some can be colored, but they may not shine nicely. Steer clear of polyester fillers like Bondo. Secondary bonding (adhesion to a cured surface) with these polyester products is always suspect for the long term.

More expensive, more trouble and better is to purchase some two-part epoxy resin, such as Interlux Epiglass colloidal silica thickening agent and a coloring agent to match your platform. The silica gets mixed with the resin to a putty with peanut butter consistency.

Note: You can repair the hole with uncolored resin, then paint on gelcoat — contact your boatbuilder and it will sell you a small can of the exact color that’s on your make and model. This is best applied with a small sprayer, like those made by Preval. Of course, even the exact color won’t be a perfect match because your boat has weathered, but subsequent weathering of such a small repair will “blend” any difference in shade after a season — maybe.

Epoxy resin offers superior adhesion and allows you to make your own putties and fillers. Courtesy: International Paints

I didn’t see the damage, so I don’t know if it was in a conspicuous place or even whether the owner cared. Some folks might be just fine sticking some cheap, pre-made goop in there for a “good-enough” finish. Others might want an invisible repair. Fact is, once fiberglass has cured, epoxy will provide the best adhesion, the least shrinkage and the most resistance to popping out or cracking once the boat gets back in service and starts to flex. And they all flex to one degree or another — the better boats less than others. This fact, plus not knowing where the boat is used or how hard the owner runs it, makes it very difficult to estimate how long a repair will last. So, I pulled all the stops.

Step 6: Apply the putty — either pre-made or one that you mixed yourself — using a plastic spreader, available where you bought the resin. “Overfill” the repair, as these products shrink on curing, and you want to sand back to flush with the surrounding area after curing. At an inch deep (which, as I said earlier, I doubt for an integrated platform), you’ll probably have to fill the hole three-quarters full. Let that cure overnight, and then make another pass to “overfill” the next day. Let that cure.

Tip: If you can make that second pass so that you just barely overfill the hole, apply a 4-milliliter sheet of polyethylene film (from a nursery or good hardware store) over the repair. Let cure. The next day peel the plastic, which won’t stick to the goop you applied. If the stars are aligned, your repair will be clean, super smooth and you’re done (you might need to use a Scotch-Brite pad to clean up any slag stuck to the area surrounding the repair area). If you chose not to use the plastic sheet trick, or the repair is rough, wet-sand with a sanding block, starting with 120 grit and working your way to 600 grit. Use the block because hand-held sandpaper will scour out your repair area, creating a depression that will show, at least in sunlight. Then apply rubbing compound, then the wax of your choice. The repair should look good.

This “nothing” repair doesn’t take two whole days. But you need to wait a day between start and finish. That means two trips to the boat. Now, just what could a repairman charge for such a small ding that would allow him to cover his time (leave his expertise aside for a moment) and not leave the boat owner with his jaw dropped to the dock? I know one guy who’ll do this kind of work — as long as your boat’s en route to his shop or other jobs and the “be-back” travel time doesn’t take more than the be-back work, which in this case might be about an hour’s fee. Otherwise, it’s “too small a job for me.”


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