Patching My Aluminum Boat by Rick Itami

Patching My Aluminum Boat by Rick Itami

I Almost Threw Away My Boat!!

Back in 1997, I got a heckuva good deal on a brand new 19-foot aluminum Grumman fishing boat with 90 hp and 6 hp Johnson motors and trailer for $13,900. I love that boat because it’s never let me down and through the years went with me to places like Montana’s famous Missouri River trout waters, the Columbia River from Lake Roosevelt to Buoy 10 and many other fishing venues in Washington, Idaho and Oregon. I can’t tell you how much joy this boat has given me over the years, allowing me to catch scores of steelhead, salmon, trout, sturgeon, bass, walleye, panfish and bottomfish.

Five years ago, my wife suggested I buy 4-stroke motors because she didn’t like the fumes from my 2-stroke engines. Being a dutiful husband, I bought new Yamaha 4-stroke 90 hp and 6 hp replacements that have worked great. I take good care of my equipment and every year the motors start right up and the boat has always proven to be safe and seaworthy.

But this year, when I took my boat out of storage and parked it in front of my house anticipating a first-of-the-year run in my neighborhood Liberty Lake in eastern Washington, I was shocked to see a pool of water under the boat. Closer examination found that I had two pinhole leaks and one more significant leak from a hole about 1/3 inch in diameter.

fix a leak in boat patch acetone sandpaper

The author was shocked to find leaks in his 23-year old boat and eventually learned how to permanently fix them himself

I went to the internet to see what options I had to repair the leaks.

The method that seemed to be the best permanent fix was to have an aluminum welder spot weld the holes shut. I looked up some local welders that worked with aluminum and found out that one must be very careful about choosing who to have such work done.

The first guy looked at the holes and said that he would fix them for $200. I was a bit skeptical about his experience and expertise because he was a younger fellow who worked out of his home with no business sign out front.

I decided to contact another welder who seemed to have a good reputation with years of experience. When I showed him my boat to get an estimate, he said that there was no way he could give me an estimate. The reasons were that he would have to take out the floor boards of my boat (no easy task) and see what was underneath, like floatation material that could catch fire with the heat of the welding. The largest hole was also right beneath my gas tank and he would have to make sure there was enough clearance to be sure the fuel tank wouldn’t explode.

Finally, he said that he had never worked on a Grumman boat before and therefore did not know what kind of bonding materials were used in the rivet seams. He said that the welding heat could melt the bonding material and cause new leaks.

Finally, he said he could fix the leaks but it could cost a lot more than I was prepared to pay. I appreciated his honesty. Finally, he suggested using marine epoxy to fill the holes and said that would be a lot cheaper and safer.

For some reason, I just didn’t think that epoxy would be a permanent fix and decided to do more research.

I called a guy who owned a fabrication business that specialized in aluminum.

When I described to him where the leaks were and what size they were, he asked if they were leaks from rivets. I said “no” and added that I could not see any dents from possible hits from underwater rocks or boulders. I also told him the leaks were not located where my boat trailer rails may have rubbed. He didn’t even have to see my boat.

He said the leaks were probably caused by electrolysis and therefore he would not want to take my money to try to repair them. I was stunned! Then he suggested that I simply purchase a new hull.

I contemplated buying a new hull and having my Yamaha engines installed on it. But I would have to find a way to get rid of the old hull. I called a local marina to see if they knew of a boat salvage business that would take care of my old hull.

The fellow who owned the business asked me why I wanted to get rid of my boat.

When I told him, he was astonished and said that I could save thousands of dollars by just patching the leaks with epoxy. When I told him that I didn’t think epoxy would be a permanent solution, he said that he owned several boats over the years and had successfully fixed leaks with epoxy that lasted forever.

He told me to come by his shop and he would sell me a marine epoxy that he uses for about $20.

I excitedly drove to the marina, bought the epoxy and then drove straight to the storage facility where my boat was located.

I followed the instructions carefully by first wiping the surfaces clean with acetone and then roughing up the areas with sandpaper. One more cleaning with acetone and I was ready to apply the epoxy.

The instructions said to combine the two ingredients in a 1:5 ratio and use a putty knife to apply the epoxy. I found the epoxy difficult to manage because it was more liquid than I had anticipated and filling the holes from underneath was sketchy at best. I spread the epoxy as best I could over the holes and then left it to dry. The instructions said to wait 24 hours for the epoxy to set up.

I went back the next day and found the epoxy was still moist and soft like clay. And it appeared that a bubble had formed just over the biggest of the holes. The instructions said that it may be necessary to use heat for the epoxy to set up properly.

I set a propane catalytic heater underneath the patches and let it run until the propane bottle emptied. I came back the third day only to find that the heat had not caused the epoxy to harden at all.

Over the next two days I ran through two more bottles of propane, all to no avail. After two weeks, I checked the patches and found them to be rubbery and not hard. I easily pealed the epoxy off with my fingers.

My guess is that the epoxy was old and past its useful life.

Totally frustrated, I went to the nearest Ace Hardware store and talked to the owner, who had always been helpful in guiding me to the best products for my needs. He handed me a small tube wrapped in packaging called JB Water Weld. He said all you had to do was cut a piece of the tubular-shaped putty and kneed it with my fingers until the color was consistent throughout. Then I just needed to press the putty into the holes and shape and smooth it to my liking. I went back to my boat and cleaned and sanded the areas once again and found the putty-like epoxy mixture much easier to apply.

The thick texture made it perfect to reach up and fill the holes and shape the epoxy with just my fingers. No bubbling occurred either.

And the next day, the epoxy was hard as rock!

fix a leak in boat patch acetone sandpaper epoxy flex seal

To repair an aluminum boat leak, all one needs is some acetone, sandpaper, marine epoxy, and a small putty knife. Flex Paste is optional.

On my own and probably because of my bias about epoxy maybe not being a permanent fix, I decided to take one more step.

As probably all of us have watched at one time or another are the commercials about Flex products like Flex Seal, which can be sprayed on surfaces and turn into a rubbery finish. The commercial that intrigued me the most was the one about Flex Paste where it showed the salesman applying the product to chicken wire molded into the shape of a boat and then taking the boat out on the water with no leaks. I decided to buy a small tub of Flex Paste and apply it over my epoxy patch just as an added measure to hopefully enhance a more permanent fix. It was easy to apply with a small putty knife and set up in hard rubber form by the next day.

As old as my boat is, I know that more leaks will turn up in the future, but now I know I can quickly, easily and inexpensively fix them myself.

I am pleased with the outcome of my research and embarrassed by my false assumptions and stupid mistakes along the way. But I hope this will help you save time and money if you need to repair leaks in your aluminum boat.

- by Rick Itami

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Your boat in storage could be susceptible to leaks if there is moisture in the seams and if freezing and thawing occurs. If your boat is dry and your storage area is also dry, you probably will be OK.

Rick Itami

We too had a older SmokerCraft that had leaks so we had LineX sprayed inside and the keel. Yes this made the boat a bit heavier but leaks were gone and keel was protected in future. I have to say it’s the older aluminum boats that I love.


I have a 16.5’ aluminum Lowe fishing boat that has been in the garage and not used for a few years. It has a riveted hull. Is it possible for the hull to develop leaks just sitting for this length of times?

James R Harvey

I have been dealing with electrolysis leaks on my 1991 Lund for a number of years. As described in the story inside access is very limited because of flotation foam and the fuel tank. I initially made temporary ‘patches’ using metallic RV repair tape. Last summer with the floor plywood having turned largely to sawdust it was time to actually fix things and a new floor deserved actual hull repair. A caulking tube of epoxy with a mixing nozzle appears to have worked great. With luck my 30 year old boat will outlast me as I am not a fan of all the plastic (even if it doesn’t rust or corrode) in the newer models. My 1650 Renegade has helped me catch Salmon, Browns and Steelhead in Lake Ontario and Striped Bass to Sailfish along all of the Atlantic coast.

Bruce Porter

Did you add another sacrificial zink to your transom?


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