Ultra-light Hull Patching Questions

[Will Derness]

I've got a Wenonah ultra-light layup canoe that has seen some action on the hull's bottom, despite my best efforts to dodge the burrs of the riverbed.

After last October's trips the canoe's bottom was pretty scratched up, some revealing the fabric layer. Last fall I mixed up some Gflex, and using a very small brush filled in the scratches. Covered with Peel Ply, let dry and sanded out rough edges. Not pretty, but it is protected.

3 weeks of paddling in Florida have now added to my hull maintenance tasks. The worst new scratch was one I saw coming in the crystal clear water, but too late to avoid. An upside down in the water metal tubular framed chair, with one of its legs projecting skyward, of course missing its rubber foot cover. Any ride over that piece of re-bar was too long.

Facing another hull touch up. I'm left with some thoughts on next steps.

1. How about using polyurethane for patching? Its inexpensive and already mixed. If I used polyurethane and didn't like the results, could I Gflex over the polyurethane?

2. Long term, my use pattern suggests I'm in for more of this. Does it make sense to roll the entire bottom with Gflex now. The alternative is to keep patching individual scars until over time it has an epoxy bottom.

Tales from the experienced would be nice to read.

 

[yellowcanoe]

not a repair guru but did you read:
http://www.westsystem.com/ss/gluing-plastic-with-g-flex-epoxy/

 

[Jim Dodd]

I would have suggested epoxy at the begining. I haven't used G-flex. I need to view Yellowcanoe's link share!
Since I use epoxy to build my canoes, that's what I'd use.
Did the G-flex blend in well with the original color of the canoe ?

I have, in the past mixed powdered Graphite, and epoxy. Then coated the bottom of a few canoes, as I was building them. It's ugly, and don't leave it in the hot Sun, very long. But it glides over rocks without any visible damage.

Now days, I double layer my bottoms, and be careful around rocks.

Jim

 

[Guest]

Long term, my use pattern suggests I'm in for more of this. Does it make sense to roll the entire bottom with Gflex now. The alternative is to keep patching individual scars until over time it has an epoxy bottom.

No, yes/no, maybe.

No. As a fellow Slacker Boatworxer I would wait as long as I could to roll another coat of epoxy on the bottom and continue making repairs to individual deep, fabric exosed gouges until then. You can wet sand those repairs flush when you get around to epoxying the entire waterline.

Yes/No. I would eventually roll out the waterline bottom, using an easier to roll and more economical 50/50ish mixture of 105/205 (or 206) and G/flex. (205/206 because that’s what I have in the shop) That involves lots of prep and post work, which is why I would procrastinate until it was really needed:

Tape off and wet sand scuff that waterline bottom, at least enough to remove any gloss/shine.
Wash the boat, alcohol wipe the area to be epoxied.
Tape and paper that waterline edge to catch any drips or sags.
Roll on the 105/205/G/flex mix, one side at a time up to the center line.



Tip out that side with a foam brush (or have a shop helper follow along behind a few minutes later to tip it out.
Roll and tip out the other half of the hull, down to the taped out cutwater.
Wait a week or so.
Wet sand that epoxy coat.
Wash, clean, blah, blah, blah.
Tape and paper that waterline edge again for a crisp paint line.
Roll out a coat of UV protectant varnish or urethane.
Tip out that UV coat.



That was Joel’s 10,000 mile hard used kevlar Rendezvous. I wish we had taken pre-treatment photos of the bottom, it was a Jackson Pollock canvas covered with random directional scrapes, scratches and gouges. I anticipate that the next repairs to that hull, a few years down the line, will be to wet sand and re-varnish (actually we used Helmsman Spar Urethane, which is holding up/on well) that sacrificial topcoat once again.

Alternatively, and perhaps better (I have not used it myself), skip the varnish/urethane coat and spring for a can of West 207 hardener with UV inhibitors, so any future repairs/recoats can be epoxy on epoxy, not epoxy on varnish.

http://www.westsystem.com/ss/207-special-clear-hardener

 

[Muskrat]

Mike, why the 50:50 mix? Isn't regular epoxy harder therefore more abrasion resistant?

Also that repair looks real nice.

Taking the lazy approach from the beginning, and due to my poor varnishing skills, I skip the varnish and sanding all together, and just use a good marine wax over a final coat of system three clear coat. That is for new builds, but I'll do the same if I recoat. I don't really care too much about appearances anyway though as I'm almost always in shallow rivers.

 

[Chip]

First of all, ignore those scratches and keep paddling. Is the boat leaking? No. Those scratches are cosmetic. Go paddling.

Ultralight canoes have a "skin coat." What is the skin coat? It has to be something more than epoxy, or UV would tear it up. Knowing how well you maintain boats, you will ignore my advice to ignore your scratches, but why use something different to patch it? I suggest patching it with more skin coat, whatever that may be. I thought the skin coat was clear gel coat, but that is just an uninformed guess.

 

[Alan Gage]

What is the skin coat? It has to be something more than epoxy, or UV would tear it up.

I believe the skin coat is nothing more than a thin layer of the resin used to saturate the cloth which, in the case of nearly all canoe manufacturers, will be vinylester resin which isn't as prone to UV degradation as epoxy.

I agree with not worrying about scratches unless they're into the cloth and in that case I usually only "repair" the problem areas rather than the whole canoe. But I'm not real concerned about aesthetics and superficial scratches don't bother me at all. I like filling scratches/gouges with cabosil thickened epoxy. Spread it on and then squeegee off the excess. One application will fill a gouge nearly flush, which is good enough for me.

Alan

 

[pblanc]

Yes, as Alan says, skin coat is nothing more than a thin layer of resin, usually vinylester these days, brushed into the mold before the first layer of cloth goes in.

Polyester resins will not cure reliably when applied over epoxy, even if the epoxy is well-cured. I don't know if the same is true for polyurethane resin.

You might use small batches of G Flex epoxy to fill in very deep scratches that go into the cloth, but I see no advantage whatsoever to using G Flex in any proportion if you plan to coat the entire hull. Apart from being more expensive, G Flex is more viscous and will not level as well. It also does not cure clear.

If you want to coat the entire hull I would suggest rolling on several coats of a low-viscosity "penetrating" epoxy like System Three Clear Coat. I have also heard of people having good results with West System 105 resin and 207 special clear hardener. A low viscosity epoxy will tend to fill in all the relatively superficial scratches, but it may take multiple coats.

 

[Muskrat]

Skin coat, is just filled weave, it isnt rolled in, it just happens as the epoxy and weave are pressed against the mold. That's why there isn't any extra weight, because there isn't a gelled coat of vinylester sprayed in first.

Edit: in a vinylester laminate, the same applies, the canoe is molded in without spraying in a gelled coat of vinylester.

 

[Glenn MacGrady]

If the scratch has reached fabric, I've always repaired it with some dabs of cheap epoxy. Scratches in the gel coat are as of little importance to me as scratches on the soles of my shoes.

That said, you can fill the scratches chemically-optically by wiping Penetrol on the the bottom, let it dry for five minutes, and then wipe it off. Shines up composite boats great. It will last almost all season and then has to be reapplied. Adds no weight. It's how Dave Curtis refreshes used boats he sells.

 

[Guest]

Mike, why the 50:50 mix? Isn't regular epoxy harder therefore more abrasion resistant?

Also that repair looks real nice.

Taking the lazy approach from the beginning, and due to my poor varnishing skills, I skip the varnish and sanding all together, and just use a good marine wax over a final coat of system three clear coat. That is for new builds, but I'll do the same if I recoat. I don't really care too much about appearances anyway though as I'm almost always in shallow rivers.

Why the 50/50 mix? I dunno, I have been using that mix with skid plates and it seems more scratch/gouge resistant than straight 105/206.

Is regular epoxy more abrasion resistant than G/flex or a G/flex mix?

I do wish I had taken a photo of that Rendezvous bottom before we recoated it. That is Joel’s second Rendezous and he wore the first one out. The bottom was almost completely white with scratches and there wasn’t a lot of resin left atop the fabric. That canoe when not in use lives almost year round on a canoe trailer, so UV was a concern.

I am assuredly no resin master; the only resins I have ever used are old school poly auto-body resins and West System.

If System Three or MAS or etc would be more UV protectant that would eliminate the varnish or urethane top coat, which is then in the way of any future resin repairs.

The best solution might be to use like materials over the existing worn resin, ie Vinylester resin over Vinylester.

I have never used Vinylester, although from working and sanding on old Vinylester hulls I have developed a slight allergic reaction to it (dust). I didn’t have any reaction to sanding the Rendezvous, which is Vinylester, although that was all wet sanding.

There are pros and cons to poly/vinyl/epoxy resins. Interesting on-topic discussion here:

http://bwca.com/index.cfm?fuseaction...ID=15&confID=1

Edit: If memory serves we rolled out/tipped out two coats of epoxy resin on that bottom before 2[SUP]nd[/SUP] wet sanding and varnishing, which is visibly in the difference between the sheen off the hull in the two photos (first coat of epoxy vs two coats and varnish)

 

[Will Derness]

Jim - Did the G-flex blend in well with the original color of the canoe ?

Yes, pretty good color wise, but the peel ply pattern is noticeably rougher than the vinyl ester OEM finish.

Chip & Alan - First of all, ignore those scratches and keep paddling.

Music to my ears here at Slacker Boats Works. I'd rather paddle boats than maintain them.

Glenn - thanks for the Penetrol tip. That sounds pretty darn easy, we like that at SBW.

Muskrat - Skin coat, is just filled weave, it isnt rolled in.

I've only recently started fixing up composites, all my previous repair work has been on Royalex hulls. I beat up my WW boat so bad, that the canoe was worn down to the foam core being exposed. My understanding is that water penetrating the foam core is not good for the survival of the hull. So I've since repaired that and all is well.

So I've unthinkingly taken the same thought process to composites. Thinking fabric exposed to water is a danger for hull integrity my approach is to cover it with something - epoxy is what I've used. But is that true? Exposed fabric nothing to worry about? Will all be just fine until you abrade a hole all the way through?

The Wenonah looks to have some foam in the bottom and the ribs, so I'm thinking water wouldn't be good for the foam. But what about a boat w/o any foam in its construction?

 

[stripperguy]

Jim - Did the G-flex blend in well with the original color of the canoe ?

Yes, pretty good color wise, but the peel ply pattern is noticeably rougher than the vinyl ester OEM finish.

Chip & Alan - First of all, ignore those scratches and keep paddling.

Music to my ears here at Slacker Boats Works. I'd rather paddle boats than maintain them.

Glenn - thanks for the Penetrol tip. That sounds pretty darn easy, we like that at SBW.

Muskrat - Skin coat, is just filled weave, it isnt rolled in.

I've only recently started fixing up composites, all my previous repair work has been on Royalex hulls. I beat up my WW boat so bad, that the canoe was worn down to the foam core being exposed. My understanding is that water penetrating the foam core is not good for the survival of the hull. So I've since repaired that and all is well.

So I've unthinkingly taken the same thought process to composites. Thinking fabric exposed to water is a danger for hull integrity my approach is to cover it with something - epoxy is what I've used. But is that true? Exposed fabric nothing to worry about? Will all be just fine until you abrade a hole all the way through?

The Wenonah looks to have some foam in the bottom and the ribs, so I'm thinking water wouldn't be good for the foam. But what about a boat w/o any foam in its construction?

Mr. Derness,
If the damaged composite is worth owning, there better not be any starved cloth in any section of the hull. All fibers must be fully saturated with resin, or should have been from the factory (or basement). As far as water absorption, the resin types will determine how much of an issue that might be. Absorption rates are different for various epoxies, polyester and vinylester resins. My memory is fuzzy on the absorption rates, but the data should be readily available.

 

[pblanc]

Aramid fibers in general are rather hydrophilic. Aramid fibers denuded of resin will absorb water to some extent. You can actually see this and once the denuded areas of cloth become damp, it takes some time for them to dry out. Some claim that water can actually be propagated along aramid fibers even into areas still incorporated in resin. I don't know if this is true, but it is a fact that resin binding to aramid is not as good as we would like it to be.

It has been my practice to try to apply resin to any areas that have become denuded. Apart from the water absorption consideration, aramid fibers "fuzz up" when abraded, and after they have done so it becomes quite difficult to get the surface smooth again.

 

[Guest]

Aramid fibers in general are rather hydrophilic. Aramid fibers denuded of resin will absorb water to some extent. You can actually see this and once the denuded areas of cloth become damp, it takes some time for them to dry out.

Good point. I always wash a boat before doing any resin work. The whole boat, inside and out; in part because I don’t want to transfer any contaminates from an unwashed area to a clean spot when working on the boat, and also because it is a good way to get up close and personal and thoroughly inspect a hull before beginning work.

After Joel’s Rendezvous was washed the more resin worn areas stayed darker/damper for longer and gave us a good idea of where the recoat line needed to start. We only needed to wet sand the glossy areas.

We let that canoe dry in my shop for a week+ before rolling on the first coat of epoxy, and I ran a radiant oil heater under the inverted hull for a few nights, just to be sure.

 

[Trevor Paetkau]

I wonder if I might chime in with a couple of general thoughts.

In addition to most fabrics needing protection from water, if fabric is exposed it will need UV protection.
Some epoxies are formulated to include UV inhibitors, most are not.
If the fabric is ripped, the structural integrity of the hull could be impacted in that immediate area, and a patch should be applied. 4 oz cloth should be enough and it's easy to fair.
Keep in mind that when applying a patch or new coating, you'll be depending on a mechanical bond between the existing product and your new product. As such, worry more about prep than the brand name of your chosen poison.

Mostly, it's not complicated at all. Just a matter of cleaning the wound, giving it a good rough up, and applying the patch/coating, followed by something with a UV inhibitor. Now getting it to look good, there's the rub ...