Repair of Hull Delamination in Old Town Discovery Sport 15


I just purchased a used Old Town Discovery Sport 15, and it has a bulge in the hull both inside and outside which I am calling delamination. Neither inside or out appears to be compromised, so I am optimistic that I can repair this exclusively from the inside. The bulge is about a foot wide. Do I have to tear into this (on the inside) and replace the inner layer with filler/fiberglass (and use a heat gun on the outside and press the bulge down to flatten it) or could I just puncture the inner side, put epoxy in it and compress the bulge, seal the hole and weigh it down until hardened? That sounds like a long shot but would love to hear any recommendations on how to flatten this thing and get back to canoeing.

Well, you have a problem that is not easy to fix. The Old Town Discovery canoes are three-layer polyethylene, rotomolded hulls. It would appear that the inner and outer solid PE layers have separated from the foam core.

The problem is that not much will bond effectively to polyethylene. Conventional epoxies won’t. West System G Flex epoxy will yield a reasonable bond to PE but only if the surface is pretreated by oxidation. For home repairs, flame oxidation is typically done by passing the flame of a propane torch quickly over the surface. This renders the PE less chemically inert by stripping away electrons from the surface of the ethylene chains but the effect is temporary. Without preoxidation the bond strength will be poor even with G Flex epoxy.

So that rules out injecting epoxy since it would not be possible to pretreat the surfaces to be bonded. You might be able to cut away the solid PE layers that have delaminated and bond them back down in place using G Flex after appropriate pretreatment but you would need to be very careful not to melt the foam core.

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I really appreciate this-- Any chance I could achieve flame oxidation on the inside of the HDPE by passing the flame torch along the outside?

As I picture this repair, I am imagining “lancing” this bulge from the inside but that the inside PE might NOT be malleable, and would need to be cut significantly to get it to lay back down. Also I am picturing a fresh layer of fiberglass being an essential part of the repair. As for the outer HDPE, I am picturing heating that up and pressing it flat with a piece of plywood once the inner bulge has been punctured so any excess air will have a place to go when I flatten the outer growth. I hope I can pull this off. Thank you again for your input.

No, you can’t flame oxidize the inner surface of the solid PE layers from the outside. Any prolonged contact of the flame with the hull will simply melt the PE. Flame oxidation is a surface treatment done by passing the tip of the inner blue cone of the torch flame quickly along the very surface of the hull and treats only the very surface.

Yes you can bond cloth to PE after appropriate pretreatment using G Flex epoxy. And I agree that it may not be possible to get the solid PE layers to lie back down smoothly on the foam core so that might be the only option.

Years back I repaired a very beat up and neglected Old Town Discovery 174 that had been pinned and had many fine cracks in the interior solid PE layer and had both stems abraded into the foam core over a length of more than a foot at both ends. I bonded a layer of fiberglass cloth down over the interior of the hull and rebuilt the stems using G Flex epoxy thickened with silica powder which was then covered with a layer of fiberglass cloth and finally a large Dynel abrasion plate. Here is a poor quality photo showing the repair of one of the stems. The very large black Dynel abrasion plate was necessary because of the extent of the stem damage.

Old Town 174

That repair has held up pretty well.

I’m far from a boat repair expert. I might try drilling a hole straight thru the hull for a half-inch bolt and then shooting G-Flex inside as much as I could. Then with a bolt and nut and big washers and two pieces of plywood with a hole in the center clamp the whole deal down tight letting the bolt pressure force the glue out. Then deal with patching the half-inch hole.

The only other way I see clamping it up is building a giant C-clamp to span around the boat.

I once did something similar in my garage but not to a boat where I blocked the part up and then used the garage ceiling joists to push against with a pole and a jack.

Where there is a will there is a way. :canoe:

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The molded boats are very hard to repair. The reason I have never owned one.
The simple answer is live with it.

It looks to me like it was stored somewhere with something heavy sitting on it. I would leave it alone and just use it as is. The lump may go away with use or at least smooth out a bit. Leaving it right side up in the sun for a few days with something heavy inside may flatten it out as well.

It doesn’t look like a hog as it goes in both directions.

Living with it is an option but if the OP is like me he will only see that blister every time he looks at it and from ether side. Every time I would run up on a rock I would be wondering if it ripped thru etc.

Here is my last idea on trying to fix it. Get some wood blocks or bricks etc that you have around and set the boat right side up supported below at the area of the bubble and stabilized so its not rocking around. Then I would drill about 10-12 eighth-inch holes from the inside thru just the inner skin. Squirt G-Flex into each hole cover the bubble with wax paper and stack weight inside the hull to force it down. I have a pile of around 400 bricks so that what I would use if you have a weight lifting set those plates would work. Before I did the glue I would do a test run to make sure I had enough heavy stuff to push it flat and tight. :canoe:

West System does pretty extensive testing of the adhesive properties of their epoxy products to various materials after various pretreatments.

Although G Flex epoxy was specifically formulated to address the shortcomings of conventional epoxy bonds to plastics, even with optimal pretreatment the adhesion tensile strength of G Flex to plastics, including polyethylene, is much less than the bond strength of their conventional 105 resin with 205 or 206 hardener when applied to fiberglass.

Here is the published adhesion data from the West System website for G Flex applied to polyethylene following three different pretreatments. The number is the tensile adhesion strength in psi:

polyethylene (HDPE) alcohol wipe, flame treat - 2312
polyethylene (HDPE) 80-grit sand, flame treat - 1813
polyethylene (HDPE) 80-grit sand (no flame treat) - 400

By comparison the adhesion bond strength of 105 resin with either 205 or 206 hardener applied to fiberglass is 7846 and 7320 psi respectively.

Needless to say, a tensile adhesion strength of 400 psi is really poor. I have found that extraneous drops of G Flex that accidentally land on non-pretreated PE can be flicked off with a thumbnail after the epoxy cures.

Would trying to bond non-pretreated PE back together by injecting it into a void between delaminated layers work? Maybe, but I suspect it would be a waste of time and epoxy.

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I really have little clue in this case, I’m assuming there was a bond at some time between the three layers and when the bond failed some of the products remained stuck to one side or the other and the repair bond then may be bonding to the mess that is left. I could be wrong and the only way to tell would be to take it apart and have a look and that seems like more work than it is worth to find out. Right now this boat may have value to the owner to get something workable but in the market place is worth really little.

The bond may be low in PSI but the area is large at a one foot dia. so at 400 PSI he would have 45,000 pounds of glue joint when cured even if that was reduced by a factor of 10 it would take some doing to get it apart.

It might be worth 25 bucks and dump a whole kit full in the void.

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The only “product” in the hull is polyethylene. Three layer PE boats of this type are constructed using a “triple dump” rotomolding process. Three separate batches of powdered PE are introduced into the rotomold but the middle batch is formulated so as to produce the foam core. But there is no additional bonding agent that holds the three layers together.

The same type of delamination can occur in Royalex hulls in which one or both of the outer solid layers of ABS delaminate from the foam core, which is also ABS.


Would you then say the idea is that polyethylene then is intended to bond to polyethylene solid to foam to solid? Or if I were to cut a square out of the hull would the three layers just fall apart as three separate sheets? If there was a bond that took place during the rotomold process do you think when a delaminating like this happens the foam layer being weakest is what split or pulled apart?

I would think epoxy could get a grip into any bonded foam still attached so the questionable side of the joint would be the solid poly. Being a rotomolded into a smooth form on the outside but not the inside is there a tooth to the surface inside the layers? I wonder if anyone has photos of a section of a scraped canoe maybe that was destroyed in a river where they pulled the layers apart. would be interesting to see.

Any idea what would cause this? It almost looks like a manufacturing process defect that came out later in life, or maybe it got too close to a campfire.

Thanks for the info.

bud16415. Normally yes, the outer and inner PE sheets bond to the foam core. Sometimes you see, even in brand new poly link boats bubbles on the inside, which could be an issue with bond or maybe just too much material in between. My experiences have been with loss of the outer layers usually and when exposed the foam core is definitely bonded (or was) to both. Since this is a Discovery Sport (square stern) and given the shape on the outer hull, I’m wondering if gasoline had something to do with this. I have seen similar although on a smaller scale when gas was spilled on a hull causing the outer and foam to kind of dissolve. I fixed that by cutting from the outside, scraping out the bad foam, filled t.he hole with felt and epoxy to fill the gap, then patched the outside.

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Thank you all for your replies-- having just bought this canoe I want to see if I can make this bulge go away. To make it more functional and to hopefully get a longer service life out of it. I simply bought it to use. Anyway, in reviewing replies, it seems to me I am going to have to cut away the top of this blister, carefully (and quickly) flame oxidize the foam and bottom HDPE layer, then lay a coat of G Flex over it. I may opt to add one or more layers of fiberglass at the same time, covering with more G Flex each time. I would anticipate that a good inch or more of overlap of the fiberglass at the edges would be a good idea. Then sand when dry if needed, and perhaps find some white paint to finish it off. I welcome any further thoughts or recommendations.

Sounds like a reasonable plan to me. But sometimes it becomes necessary to alter a plan as the repair proceeds.

I recently repaired a Royalex canoe in which the outer layer of solid ABS had delaminated from the foam core on the outside of the hull bottom amidships. I found that a Dremel tool with a cutting wheel worked pretty well to cut around the periphery of the delaminated outer layer.

I would be very careful flame oxidizing the foam core as it is easily melted. All of the little interstices formed by the cells in the core may provide enough mechanical footing for the epoxy to get an adequate hold even if the bond strength is a bit less than optimal.

When bonding the delaminated external outer layer of solid PE back down I would try to find something relatively flexible, like thin aluminum sheet, to place over the area of repair and then use something like cam straps or ratchet straps around the whole hull that will keep the PE in approximation with the core as the epoxy cures.

If you do cover the area of external repair with cloth I would plan to overlap the intact, undamaged hull by at least 2 inches. You will want to cover the area of repair either with a varnish or polyurethane with UV blocker, or an opaque finish like paint to protect the epoxy from UV degradation over time.

Greetings-- thank you for this. My plan is to only repair from the inside of the canoe. regarding the outside I was thinking of placing a piece of plywood underneath the hull but you’re a step ahead of me regarding the curved portion. I’m not sure if I can find a thin aluminum sheet… never seen a source of those in my 59 yrs… but will stew on the matter of what else might follow the curve of the hull and push the bulge flat on the outside at the same time. Maybe a few sheets of cardboard with the corregation pointing fore and aft…?

Any sheet metal shop or shop that does metal fabrication can supply a piece of aluminum any size and thickness that you want.

It will be interesting to see what you find when you cut into the hull. I would be surprised if all three layers have delaminated, but it’s possible. Sounds like a manufacturing defect that may have been under the lifetime warranty for the original owner. Can’t think of many thing that would cause this kind of deformation unless a concentrated high heat source broke down the foam core releasing and expanding the trapped gases.

Keep in mind that only the deformation on the outside of the hull may affect performance.

A thin piece of wood or synthetic paneling may have enough flexibility to conform to the hull.

If you must use cardboard, which would certainly be better than nothing, I would use multiple layers of solid, non-corrugated cardboard. Corrugated cardboard will tend to simply crease when bent.

Many thanks-- concur that performance may not be affected… I just don’t want this thing to spread.

Just trying to understand. What gas do you think is inside the bubble? I don’t think it is air. When you push on the bubble the air doesn’t push out and then suck back in? I think it is trapped in there and something likely heat caused the foam core to melt and outgas. I have to wonder if you drilled a tiny hole from the inside if the two sides would come in some. If heat softened the sides and they stretched and cooled there would be too much material to be forced down flat again without reheating. If you cut out the inside and push the bottom in it may well pop the other way and then you would have a dent in the bottom.

I think I would start with a tiny hole in the center from the inside.