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 Post subject: Skid Plate repair
PostPosted: July 24th, 2016, 8:21 pm 
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Location: Cincinnati, Ohio USA
I have an old Mohawk Royalex canoe that I've added fiberglass tape skid plates to over the years using polyester resin from the auto parts store. I was thinking about using a kevlar skid plate kit this time with the hope that if I do a good job, I'll never have to do it again. The kits I've seen on line look like they use epoxy resin. Will that bond to the polyester resin?

If not could I buy the kevlar strips somewhere and use autoparts polyester resin? If so, any thoughts about U.S. dealers who might have the kevlar?

Thanks,

Fritz


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 Post subject: Re: Skid Plate repair
PostPosted: July 25th, 2016, 12:53 pm 
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Location: Freeland, Maryland USA
Fritz wrote:
I have an old Mohawk Royalex canoe that I've added fiberglass tape skid plates to over the years using polyester resin from the auto parts store. I was thinking about using a kevlar skid plate kit this time with the hope that if I do a good job, I'll never have to do it again. The kits I've seen on line look like they use epoxy resin. Will that bond to the polyester resin?

If not could I buy the kevlar strips somewhere and use autoparts polyester resin? If so, any thoughts about U.S. dealers who might have the kevlar?


Fritz, without photos of the existing skid plates it is hard to offer much advise or opinion.

If you mean the manufactured skid plate kits I believe most of them now come with epoxy resin. Back in the day they were (I think) some kind of uber-stinky cancer causing in California urethane resin. Old Town kits were the last I found with urethane resin.

In any case I would avoid the kits that come with yellow kevlar “felt”. That kev felt material is included only because it is easy to apply, but it is crap for abrasion or even impact resistance, and the kit cost for the materials included is absurd.

Epoxy resin should bond to poly, but that is then only as secure as the poly adhesion below.

If your glass tape and poly resin skid plates are relatively flush and smooth to the stems the easiest and most effective repair would be to cut a larger, overlapping piece of dynel fabric and install it with epoxy resin (or even a mix of G/flex and West System resin, or even better straight G/flex) and cover it with peel ply to reduce the tendency of dynel to swell when saturated.

Dynel has superior abrasion resistance; you already have a glass underneath for blunt force impact, and a glass/dynel layer combination offers the best of both worlds.

Pblanc (I think) and others have on-line photo tutorials for installing dynel skid plates.

For a US supplier of dynel and (release treated) peel ply I’d suggest Express Composites. Sweet Composites has both, but their only peel ply is green pull nylon, which requires some epoxy set up timing to peel off.


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 Post subject: Re: Skid Plate repair
PostPosted: July 26th, 2016, 11:56 am 
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Quote:
For a US supplier of dynel and (release treated) peel ply I’d suggest Express Composites.


Express composites doesn't carry Dynel. I called and verified this a month or so ago. I got mine from Raka. They sell it as "Xynole" but from what I could find they're effectively the same thing.

Alan


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 Post subject: Re: Skid Plate repair
PostPosted: July 26th, 2016, 12:00 pm 
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Posts: 184
I agree with Mike. The Kevlar felt that was and is widely used for skid plates achieved a popularity it did not deserve. The felt consists only of very short fibers that are compressed into a cloth. The short fibers are individually tough, but since the are mechanically only connected to each other by resin, the entire structure lacks strength.

The felt material has myriad interstices that sop up resin like a sponge resulting usually in a too high resin/fiber ratio which makes the skid plate unnecessarily thick, and heavy and simultaneously brittle. For relatively gentle abrasion resistance the Kevlar felt might be acceptable since it is thick, but the impact resistance is so poor that it is very common for big pieces of the skid plate to break off with significant impact. I have seen this literally hundreds of times on Royalex whitewater canoes that had Kevlar felt abrasion plates applied.

A problem with Royalex boats is resin adhesion. I have seen repairs done to Royalex boats using conventional epoxy that initially looked good and did last for a while only to have the entire patch flake off intact. Much better adhesion to ABS can be achieved using West Systems G Flex epoxy which, when cured, will have an elastic modulus much closer to that of the ABS core. Epoxy, including G Flex, will bond to polyester. I would first test the adhesion of the existing fiberglass patch by getting under the edge of it with a wood chisel and seeing if it will separate fairly easily. If so, I would remove the existing patch and polyester resin residue.

At least in theory you can achieve a stronger bond if you apply your fabric directly to the ABS rather than the surface vinyl. This requires removing any vinyl that has not abraded away, however. Sometimes this is pretty easy to do and other times it is not. You can try getting under the outer vinyl layer with a wood chisel and shaving it off. You can also sand it off, but it might require more time and effort than you imagine. Either way, you need to try to avoid thinning out the underlying solid ABS stratum of the Royalex, or gouging it up too badly. I would certainly remove any loose vinyl, but if you can't expose the ABS without damaging it too much, leave the vinyl be.

Either ABS or vinyl needs to be roughed up and thoroughly cleaned before applying epoxy. I would use something like 80 grit paper and a power sander if available. I then wash the surface with soap and water using something like Simple Green if it is really dirty. Then rinse well and wipe down thoroughly with denatured alcohol. I usually also do a final wipe with acetone, but be aware that acetone or MEK dissolve ABS. As long as the solvent does not pool it flashes off quickly enough to do no damage. But I would not get any acetone or MEK into the foam core if any is exposed.

Either fiberglass or Dynel can be used for abrasion plates. A single layer of 5 oz/sq yd Dynel is usually sufficient and will result in a significantly thicker plate than a single layer of 6 oz/sq yd fiberglass since the Dynel fibers soak up more resin. It will still be much thinner and smoother than a Kevlar felt plate, and Dynel resists abrasion very well.

Feel free to peruse the photos in this album. These describe a rather extensive repair of a Royalex boat that had many cracks requiring both internal aramid and external S fiberglass patches, but I also applied abrasion plates and a full-length keel strip consisting of a single layer of 5 oz/sq yd Dynel plain weave fabric:

http://www.flickr.com/photos/42020723@N ... 7942924708


Last edited by pblanc on July 26th, 2016, 1:54 pm, edited 1 time in total.

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 Post subject: Re: Skid Plate repair
PostPosted: July 26th, 2016, 12:03 pm 
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Joined: August 14th, 2012, 10:19 am
Posts: 184
Jamestown Distributors sells both plain weave Dynel fabric and a good quality treated release fabric:

Dynel: http://www.jamestowndistributors.com/us ... +%2F+Cloth

Peelply: http://www.jamestowndistributors.com/us ... o?pid=3754


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 Post subject: Re: Skid Plate repair
PostPosted: July 26th, 2016, 2:37 pm 
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Location: Cincinnati, Ohio USA
Thanks all for the help with this, especially for steering me away from the kevlar skid plate kits. I'll probably go back to the polyester resin and fiberglass cloth skid plates due to cost and easy availability. The canoe get relatively little use and then most for friends or family on local float trips. The existing plates lasted maybe ten years with this kind of use.


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 Post subject: Re: Skid Plate repair
PostPosted: July 26th, 2016, 2:40 pm 
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Mike McCrea, back in 2002 you provided me with instructions on how to replace rotted wood gunnels with aluminum ones on a used MR Kevlar Explorer that I'd just bought. Still got the boat and think of your kind help often when I use it. Thanks.


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 Post subject: Re: Skid Plate repair
PostPosted: July 27th, 2016, 11:32 am 
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Joined: June 28th, 2001, 7:00 pm
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Location: Freeland, Maryland USA
Fritz wrote:
Mike McCrea, back in 2002 you provided me with instructions on how to replace rotted wood gunnels with aluminum ones on a used MR Kevlar Explorer that I'd just bought. Still got the boat and think of your kind help often when I use it. Thanks.


Fritz, you either have a helluva memory or good records.

I am pleased those 14 year old instructions worked out. I have gotten better at canoe repair over the years, but putting aluminum gunwales on a Royalex canoe remains an unwelcome task.

The varying width of RX material along the sheerline, thin in the middle and thick towards the stems, is a PITA to deal with when seating a one piece aluminum gunwale channel, best accomplished with a couple of helpers, a couple of wide metal bladed putty knives, a rubber mallet and lots of swearing.

If I ever do another aluminum regunwaling on a Royalex canoe I will try using a two-piece gunwale system with separate inwale and outwale sections.

Back to the skid plate repair/replacement. Even skipping the Dynel and peel ply materials it would be worth buying some G/flex epoxy. The small $25 size with two 4oz bottle of A and B would probably saturate your replacement glass with some left over for future uses.

G/flex would be far superior to auto-store poly resin and I guarantee you will find use for the leftovers. G/flex is simply amazing stuff and with proper surface prep sticks to damn near everything, and because it mixed with an easily eye-balled 50/50 ratio you can make as tiny a batch as needed.

G/flex is my go-to adhesive for all sorts of household things, even (or maybe especially) when I need only a pea sized batch of epoxy resin for some tiny repair. I used some a few days ago to glue a broken section of plastic refrigerator door handle back in place.

The most impressive example of a G/flex repair remains the decorative ceramic top on the humidifier pot atop the wood stove. The top was dropped and broken into several pieces. I glued the pieces back together with G/flex. That was at least 4 or 5 years ago.

That pot spends the winter atop the wood stove, full of boiling water and steam, and it is still going strong.

Buy some G/flex. You can thank me again in 2028.


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 Post subject: Re: Skid Plate repair
PostPosted: July 27th, 2016, 11:52 am 
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Joined: December 19th, 2006, 8:47 pm
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Location: Rattlesnake Pond ME
thanks for the help on refrigerator door /drawer repair. all the handles have broken!
Now another item on the Honey Dew list.


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 Post subject: Re: Skid Plate repair
PostPosted: July 27th, 2016, 1:04 pm 
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Mike, I remember you because you were so generous with your help, by the way it was a kevlar boat, not royalex, and because over the years you have posted regularly on this an other paddling sites, thoughtfully and with humor.
I'll check out the gflex, sounds like a wonder material!


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 Post subject: Re: Skid Plate repair
PostPosted: July 28th, 2016, 9:38 am 
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Location: Freeland, Maryland USA
Fritz wrote:
I'll check out the gflex, sounds like a wonder material!


You won’t be disappointed, for either skid plate installation or general epoxy repairs.

By way of illustrating the bonding abilities of G/flex here is West System’s G/flex surface prep chart:

http://www.westsystem.com/ss/g-flex-epoxy-adhesion-data

The “flame treat” for ABS is simply touching the blue tongue of a propane torch briefly to the hull surface.


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 Post subject: Re: Skid Plate repair
PostPosted: July 28th, 2016, 11:09 am 
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Thanks, Mike


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 Post subject: Re: Skid Plate repair
PostPosted: July 29th, 2016, 11:38 am 
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Fritz, one more thing with G/flex. It is more viscous than other resin mixes, and it helps to have the A and B bottles warmed before mixing so the cloth wets out easier. I just set the bottles in a pan of warm water, or even place them briefly inside my truck under the summer sun. Not hot, just less viscous warm.

If I have convinced you to try using G/flex I’ll dip into your wallet one more time.

Release treated peel ply is another wonder-product when laying glass or other materials with resin. Seamed edge fiberglass tape especially. The selvage tape edge that always stands a bit proud and sharp disappears under peel ply, and when the peel ply is removed the resin distribution is even and all that is left atop the fabric is a faint matte finish.

Peel ply largely eliminates the need for sanding and any frays or stray are far less apparent. It also reduces the tendency of Dynel to swell to sweatshirt thickness. With release treated peel ply I keep pressing it into the Dynel with my gloved palm every half hour or so until the resin has set. Same with the seamed edges of glass tape, that selvage edge vanishes.

Even with Dynel the cloth comes out so tight to the hull that it’s hard to tell the material is there.

I will never lay cloth and resin again without using peel ply, and regret every time I had ever done so without using it in the past. 20 years of boat tinkering without peel ply; Gawd that woulda saved a lot of time and effort, and looked so much better.

The results using peel ply are visibly superior, the need for sanding is reduced or eliminated and, for skid plates the perimeter edges, where skid plate are most prone to separate or adhesion fail, are seamless tight against the hull. (Also read “Zero skid plate gurgling at the cutwater”)

See Pblanc’s links about to Jamestown Distributors.

And. . . . if you are ordering peel ply, well, there’s the amazingly abrasion resistant Dynel.

BTW, Dynel, or at least all of the Dynel I have used, cuts with a clean fabric edge and has far less tendency to fray when wetting out, even when cutting fabric curves or going diagonally across the weave, so a custom shaped wear-area elongated teardrop of cut fabric doesn’t become a nightmare of frayed edges.

When I need a skinny linear patch or repair I use glass tape, mostly because the selvage edges mean the only possible frays occur only on the cut ends. Dynel is at least as easy to cut and wet-out manipulate

Dynel over the existing fiberglass, with G/flex resin, compressed with release treated peel ply. That is pretty much State-of-the-art DIY skid plate technology and makes for a surprisingly easy install.

If you are going to use the highly-recommended G/flex a yard of Dynel and a yard of Peel ply (enough for several canoes) is only another $28. Got any other canoes that need skid plates?


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 Post subject: Re: Skid Plate repair
PostPosted: July 29th, 2016, 12:16 pm 
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Location: Cincinnati, Ohio USA
The peel ply sounds like another wonder material. Seems like I may be making an order to Jamestown soon.


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 Post subject: Re: Skid Plate repair
PostPosted: August 5th, 2016, 9:56 am 
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Location: Freeland, Maryland USA
Fritz wrote:
The peel ply sounds like another wonder material. Seems like I may be making an order to Jamestown soon.


Fritz, what all did you order, or plan to order?


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