Royalex Repair

I have a Dagger Genesis that the royalex has started to crack on the bottom at the centerline. It is about 7" in length. I have read other topics and have purchased the materials that I will use. This will include G/flex 650 (two four ounce kits for a total of 16oz), Dynel cloth, and graphite powder. I have installed kevlar skid plates on other boats in the past so I am sure the process of wetting the cloth and applying to the boat is pretty similar.

My question is how do I go about removing the damage (assuming that I cut it out)? How far from the centerline should I cut? What do I fill the void with once I cut it out?

Any help or tips will be appreciated.


Does the crack go all the way through?
If the crack is only on the hull exterior and there is no visible damage on the hull interior I would gutter out the crack from the outside only. If the crack goes all the way through, I would gutter out the crack from both inside and outside forming V-shaped troughs that extended half way through the hull thickness from both sides.

If the crack is only on the exterior, I would unroof any area where the foam core is separating from the solid layer of ABS. then bevel the edges of the exterior solid stratum of ABS. The void into the foam core can be filled in with G Flex thickened with silica powder if you have enough. This works well but usually requires multiple applications to build the void up to the level of the adjacent hull. After doing so, sand it flush so that your cloth lays flat.

Some folks have reported good results filling voids in the foam core of Royalex with Gorilla Glue or JB Weld.

If the crack extends all the way through I would apply patches on both sides. I usually prefer aramid on the interior and S fiberglass on the exterior but Dynel will work. With fiberglass and aramid I usually use a two layer patch, but Dynel soaks up a good bit of epoxy and 2 layers might be rather thick. You will need to use at least two, and possibly three epoxy applications if you want to completely fill the weave of the Dynel for a smooth patch.

Exterior Only
The crack is on the exterior of the boat only.

I have some JB Weld laying around, I may look into this process for filling the void. I also have Gorilla Glue so that would always be an option.



fix royalex
Nice post by pblanc.

Two coats of epoxy is different…
from what I have done in the past with the kevlar. I would just wet the kevlar and roll it out and let it dry in place. With two coats of epoxy on the dynel, would I wet the cloth and place it, then let it dry. Once dry would I apply the second coat, let it dry and sand?



Got to order some Dynel and get some
experience with it. Back in the 70s it was believed that Dynel was wonderfully wear resistant but not at all strong. But subsequent reports suggest they’re making the stuff stronger.

I have a nice, five year old, wear patch on the outside of the hull of my OC-1, directly under my avoirdupois. There was no exterior crack, but the vinyl had worn off. I used two concentric layers of S-glass with West epoxy. The patch has been much abused, has worn like iron without cracks or gouges.

Old observations in Wallbridge’s Boatbuilders Manual held that S-glass was second only to Dynel in wear resistance. I think Dynel slips by through some magical slippery trick, while S-glass is just hard and kinda tough.

Didn’t notice whether pblanc mentioned this, but some like to remove the vinyl from the Royalex and bond the patch directly to the ABS layer. The vinyl can be skimmed off neatly by using a half inch chisel pushed at a low angle, also angling the blade a bit from the line of travel. The vinyl should come off right at the boundary layer with the ABS.

Here’s What I Did
On the crack I had I kind of V’d out the crack to get any loose stuff off and I wanted the V anyway for the filler. I used G-Flex and filled in the crack, covered it with wax paper which I covered with masking tape to keep it smoothed down. Waited overnight, took off the tape and waxpaper. Comes out so smooth you don’t have to sand. I then covered that with a layer of resin and cloth.

Dynel is thicker then the other cloths but I think from my use of it much more durable. Granted it won’t smooth out so your patch might be more obvious and if that is a concern go with S-glass. The other thing I do is add G-Flex to the resin mix and I have found especially with skid plates this really makes for a tough finish. Just my 02 worth from a few rebuilds.


I know a lot of folks like to first wet out their cloth on a transparent plastic surface, then transfer the wet cloth to the hull and I can see that makes some sense if you are applying a multi-layer patch. When I try this I usually find it messier and somewhat harder to keep the cloth properly aligned as it is laid out on the hull.

I usually prefer to wet out the cloth in place on the hull. If your cracks are relatively linear in nature, I would cut out your Dynel patch so that the fibers cross the crack at a 45 degree angle as much as possible, which usually means cutting out a long patch on the bias. If you can do this, it results in twice as many fibers crossing the crack than if you cut out the cloth so that the weave (or the warp) is aligned with the crack. Cutting on the bias also tends to reduce fraying along the patch edges.

To minimize the mess and get a nice sharp edge to your epoxy line (which is particularly desirable if you are going to add graphite powder to the epoxy) I would mask out the areas to be repaired with masking tape. I like to overlap the edges of any cracks by 2 inches in every direction. The mask also helps you keep the cloth properly aligned as you wet it out as the cloth (which is a loose weave) will want to change shape, trading length for width, or vice versa, if you are not careful. Position the mask so that it will be about a half inch or so outside the outer margin of the cloth patch all the way around.

I will usually apply some epoxy to the hull before laying on the patch. If you have a long, linear patch, it often helps to roll it up carefully as you lay it on the damp hull, then roll it out to length. The Dynel fibers really seem to take up the epoxy much more so than fiberglass or aramid, so even if you very fully wet out the cloth, after it has cured or partially cured, the Dynel fibers will have swelled up above the resin surface. Sometimes I will remove the masking tape when the epoxy is still a bit green. You may need to cut any Dynel fibers that might have frayed and are extending over the masking tape. If you want a really smooth edge to your patch, I would suggest letting the wet out coat of epoxy fully cure, then wet sand the patch edge to fully feather it. I haven’t used peel ply with Dynel, but I don’t know any reason you couldn’t.

After feathering the patch edge I apply masking tape again along the epoxy line edge and at least one more coat of epoxy. If you have wet sanded the entire patch, you don’t need to do any additional washing of the epoxy. If you haven’t, you should wash and rinse any fully cured epoxy to remove any possible amine blush. If you are applying more epoxy over partially cured epoxy, you don’t need to do this.

You will find that the G Flex instructions suggest pretreating the ABS surface with flame oxidation. I have repaired Royalex hulls without doing this and the bond has been fine, but it is easy to do if you have a hand-held propane torch. Just pass the flame quickly over the hull surface so that the tip of the inner blue cone of the flame contacts the hull surface. Move quickly as you don’t want to melt, or even heat the ABS surface.

I don’t think Dynel is as strong as fiberglass of comparable weight, especially S 'glass, but it is quite strong and does seem to be quite abrasion resistant.

What I learned
after the first coat.

To this point. I V’d out the crack into the foam core. It was approximately 16" long in the stern of the boat all along the centerline. Got all the dry rot out. I then used JB Weld to fill the void; 1 healthy coat to fill with tape around edges to keep it clean. Sanded it smooth then applied a second coat to fill the last of the void. Sanded that coat and am real happy with results. I then taped the Dynel to the canoe along the bias (Basically I have a 5’ long skid plate all along the stern). Measured everything from the centerline and basically had a 5’ x 5" skid plate. Was able to mark the canoe with a fine point sharpie right through the Dynel. Taped everything up and gave myself an extra inch all around the cloth. Decided to go ahead and add a smaller skid plate to the bow since our new whitewater park has a wave that I crash into the concrete when I drop in. Proactive rather then reactive.


  1. Don’t be proactive when you don’t know how far Gflex will go.
  2. There is no wetting the cloth with Gflex. It has the viscosity of tar.
  3. Account for approximately an inch of stretch of cloth for every foot. I overshot my tape by 4" and I had 2" of extra space, so a 5’ foot strip stretched 6".
  4. Simple Orange does a good job of getting that shit off you once your arms and hands are covered (mine was still wet).

    I am sure that I will learn a lot more once I apply the second coat. My guess is that I should pull the tape while the Gflex is semi wet, but it was such a pain to get it in place so I will leave it for now and sand.


try warming the G Flex

– Last Updated: May-08-14 8:06 AM EST –

I have applied abrasion plates to about 15 Royalex canoes using 5 oz/sq yd Dynel and unthickened G Flex epoxy. At ambient summer temperatures at least, I have had no problems with G Flex wetting out Dynel cloth, but it does take longer for the resin to saturate the fibers so patience is the key.

If you are having difficulty getting the cloth wet out, you can reduce the viscosity of G Flex by warming the mixed epoxy a bit. This will reduce the pot life some, but that usually isn't a big problem since G Flex has a pretty lengthy pot and working life. You can also try warming up the hull over which you are going to lay your cloth by wafting a hair drier or heat gun over it, and applying a thin coat of G Flex to the hull before laying your cloth over it.

How to wash
Just put the second coat on this morning, but rain has moved in and I want to give it a little more time to cure.

This coat took about 3/4 of my second G/flex kit or 6oz. Did not go as far as I thought. Happy with the results though, assuming they hold up.

Peeled the tape after the coat cured for 3 hours and it came right up with a crisp edge. Still need some sanding to feather the edges.

There is a slick, greasy, oily feeling to the patch. I assume that is what needs to be washed. What do you use to wash it? Soap, alcohol, or something else?



dilute soapy water
When feathering patches I often wind up wet sanding the entire patch to get a smoother result. That pretty well removes any amine blush.

If you don’t want to do that, just use warm water with a little bit of dish washing detergent mixed in. Rinse well afterward.

I will usually give it a once over with alcohol (isopropyl or denatured) just before applying another epoxy coat.