Poly boat repair: weld vs G-flex?

Hi all-

I'm preparing to fix a couple cracks in a poly boat. They're above the waterline, and appear to be stress cracks from some mounting screws being over-torqued into captive nuts that were molded into the boat when manufactured.  Totally non-structural area, and likely out of the way of any stresses that might come from use/ storage/ carry handles.

Wanted to ask if the hive has a preference for plastic welding or Gflex 450 as I've got both on hand.

Unless I hear otherwise, my plan is to weld.

I've got a harbor freight welding kit (the $17, 80 watt, soldering iron style one) that I'd use to melt some new #2 HDPE plastic from a homer bucket into the cracks (prepped by drilling out the crack ends, gouging a trough for the new plastic), then melting some of the steel mesh from the kit into the hull to reinforce, then melting some more plastic over the mesh.

Any input would be appreciated.

I've also got a heat gun with various deflectors and reducers available to me, and a couple propane torches (though my practice runs on 5 gallon bucket lids with that turned out, um, less than good...the results from the welder looked much better).

Thanks,
Ron

Where is the crack? Do you have pictures of it?

In general I would go with plastic welding. I have welded many kayaks using a reducer nozzle on my heat gun. If you call the manufacturer of your kayak, they may have scrap plastic and welding rod that matches the color of your kayak.

These are the videos I followed to make my repairs:





Steps to repair the crack:
1) Using a dremel or chisel, make the crack slightly wider and deeper (v shaped channel) so you can melt more plastic into the channel and shape it.
2) Clean the area real well. Soap and water followed by alcohol. You need to remove all oils.
3) Holding the heat gun a few inches from the crack and heat up the plastic with a swirling motion to avoid overheating a spot. When you see a sheen develop on the plastic, stop. At this point the plastic is just about melted and ready to weld. If you heat the plastic too much it will sag.
4) Heat the end of the welding rod until it starts to droop slightly. It is now ready to be applied.
5) Place the end of the welding rod above the crack and heat BOTH the crack and welding rod. Then using a swirling motion, push the melted welding rod into one end of the crack, slowly swirl it as you work it along the entire length of the crack. When you get to the end of the crack, give the welding rod a quick twist as you lift it off the boat.
6) Use a putty knife or some other tool to shape the weld bead while it is still hot.
7) After you finished smoothing out the weld bead, let it cool and inspect your weld. If the crack is deep, you may have to put down a second bead on top of the first.
8 ) Sand the weld bead to make it smooth. The repair will be noticible, but if done correctly it will hold.

I would definitely go with the weld.  As krusty was saying make sure it is clean before welding and the prep you both mentioned sounds good.  To stress another thing he said: don't over heat the spot you are welding!  I use ths cheapo hobie iron welder and this is fairly easy to do.

Lastly, I would recommend not adding any material other than hdpe (keep the metal out).  This will make it a lot simpler and likely just as strong.  If you want more support add larger washers to your hardware when you reattach.

Cheers,
Joseph

Thanks for the input! No pix unfortunately. Crack is located at the tip of the bow in front of the handle, near the top of the boat.

I gather you'd suggest not bothering with the reinforcing metal mesh?

I talked to the maker of the boat. They recommended hot air welding if a crack is accessible, g-flex if it's not. No scrap available; they pointed me to top-kayaker or Harmony if I wanted to buy some of their rod. Planning for now to use some thin trimmings off a homer bucket as it's a decent color match to the boat.

The crack is easy to get to, so I'm going to do it from the inside where it'll be less noticeable, and touch up the outside as needed.

At this point, I'll plan on going as you describe with a heat gun + reducer/ spackle knife to smooth.  Maybe the harbor freight welder to further smooth if necessary. It was pretty easy to weld a paint bucket with it.

I get you about the sagging: when I was practicing this morning on a paint bucket lid, I tried a torch, and that happened nearly instantly, so I think I'll try the low setting on the heat gun

I saw another post here talking about it being a good idea to have some ice water/ cold towels on hand to cool the plastic in a hurry if things get away from you, so I think I'll do that too.

Thanks!

I would definitely go with the weld.  As krusty was saying make sure it is clean before welding and the prep you both mentioned sounds good.  To stress another thing he said: don't over heat the spot you are welding!  I use ths cheapo hobie iron welder and this is fairly easy to do.

Lastly, I would recommend not adding any material other than hdpe (keep the metal out).  This will make it a lot simpler and likely just as strong.  If you want more support add larger washers to your hardware when you reattach.

Cheers,
Joseph

Thanks, Joseph!

I shall keep the mesh out of the works, that'll make the repair simpler and look better for certain.

Funny thing about the hardware: it's actually molded into the plastic, not backed by washers/ nylocks as most things are on my other boats. This is precisely where the crack originates.

I've only seen this done on my fiberglass beater SIK, and only on places that are hard to get to (bow handle, no bulkhead compartment, 5' up from the cockpit). Seems like an iffy design choice for an easily accessed location.

Ditch the metal mesh. It is not needed unless you have trouble keeping the 2 sides of the crack together.

Do the repair from the outside of the kayak. You will need the space to maneuver.

Remember you do not need to repair the entire crack in 1 pass. If the plastic starts to sweat excessively, stop before it sags. Let it cool off before continuing with the repair.

Ditch the metal mesh. It is not needed unless you have trouble keeping the 2 sides of the crack together.

Do the repair from the outside of the kayak. You will need the space to maneuver.

Remember you do not need to repair the entire crack in 1 pass. If the plastic starts to sweat excessively, stop before it sags. Let it cool off before continuing with the repair.

 

Did the repair this morning.

Drilled the ends of/ cleaned/ widened the wound, hit it with 91% isopropyl a few times, then used hot air to get both the boat and repair material gummy, kept up with that as I twisted new plastic into the crack so the boat and rod plastics merged as best I could.  I then used the soldering iron type welder to smooth out the patch.

Also got inside the hull to try to shore the repair up from the other side. Yes, you guys were right, total PITA. I managed to get a bit of plastic in the crack, but it would not have been nearly enough to trust if I'd only done the inside as was my original plan. I don't think this is going to reopen, but if it does, I'll reweld the outside, and gflex/fiberglass cloth the inside.

Still, turned out fairly well for my first attempt at such a thing, and the homer bucket matches nicely.

I also figured out what the hell caused the issue in the first place: the track's end bolt-hole was misaligned to the hull's captive nut on both sides of the boat.  Overshot the nut by about 1/8", thus there was a constant pressure pushing that nut (where the crack happened) forward (the rest of the track is riveted in). I widened the hole in the aluminum enough so the track bolt properly aligns to the nut. Hopefully this will remove the stress on that point of the hull.

Thanks for the help!

Ron

Thing I also learned: if you're going to use a screwdriver to keep the track out of the way, keep in mind it'll heat up with hot air too, and melt the plastic if you let it 

At least I didn't melt the track into the boat!

Good job on the repair.

Which kayak is that? Never seen tracks on the side of hull before.

Good job on the repair.

Which kayak is that? Never seen tracks on the side of hull before.

Thanks!

It's a Wilderness Systems Commander 120 hybrid canoe/kayak thingy that I just picked up for my wife. Didn't notice the damage until I got home. Not surprising as it's not in a high-impact zone, and was largely hidden by the track.

The tracks are a great idea (just poorly executed on this specific unit). They run the entire length of the boat on both sides; anchor trolley is on one side, paddle holder on the other, and the deck bungees hook into the track so you can move them around as needed. It's also got some shorter (18" or so?) tracks on the gunwales which will be nice for rod holders and the like. This one came with 2 deck mount rod holders behind the seat too.

https://www.wildernesssystems.com/us/products/commander-120

Gonna hit Del Valle with it on Monday for a maiden voyage.