C-Forum

I'm planning to purchase some fabric to have on hand for potential boat repairs. I just inherited a Millbrook Flashback that I'm sure at some point will require some repairs. I also have a Royalex Penobscot that we race and is, as a result, "More machine than man" in a few places.

I'm wondering what type & weight of fabric people typically use (or ideally would use) for repairs. I expect I'll order from Sweet Composites as they have a large selection. E-Glass or S-Glass (or something else)? 2oz, 4oz, heavier? I expect to use G/Flex as the epoxy if that makes any differences.

Thanks,
Eric

Note that glass you use for repairs will bond better to resin if the glass cloth is "fresh" from a supplier, rather than having been lying around your basement for more than a year. For minor patching, old glass is probably OK, but for a major repair, fresh glass is better. It has to do with the Silane coating on the fibers.

Talk to Sweet about what S-glass weave to buy that will soak up G-flex effectively. S-glass fibers are very fine, and it does not wet out easily.

Kevlar does not age if it is kept dry and stored flat. Carbon also is not coated and only needs to be kept clean and dry.

The usual rule for patching is, glass outside and Kevlar inside. Ask about exceptions. Basically, if future stress will put the patch in tension, Kevlar works well. If future stress puts the patch in compression, glass is better.

also when you talk to jennifer at sweet composites (i would reccomend calling to place your order, she is very knowledgeable and can help talk through your repairs) ask her about dynel as a repair option, it's basically a cheaper kevlar that can't be called kevlar due to trade mark infringement. she really helped talk me through a repair of my old cayman c1 slalom boat. +1 to the idea of not buying materials until you have to.

jaywolfe, do you mean *diolen* the polyester, rather than dynel the slippery exterior cover? Diolen makes a tolerable outer layer because it wears fairly smooth, but should be used only for tension repairs, like Kevlar.

I have used both the style 6522 and the style 6533 S 'glass from Sweet Composites extensively. These are both plain-weave fabrics and I have had no problems wetting them out with G Flex epoxy. The style 6522 is a 4 ounce/square yard fabric and the 6533 a 6 oz/sq yd cloth. I would stay away from the satin weave S 'glass fabrics as they can be harder to wet out. I have also used a lot of their style 500 aramid cloth, which is a 5 ounce/square yard plain-weave fabric.

You can certainly use G Flex epoxy but for bonding cloth to a composite boat I would prefer a conventional epoxy such as West Systems 105 resin with your choice of hardener (I prefer 206 hardener for most applications). This will wet out both aramid and fiberglass cloth more quickly and a bit more easily than G Flex and it cures relatively clear, whereas G Flex is somewhat honey-colored when cured.

I have also used a good bit of Dynel (5 oz/sq yd). It is not as strong as S 'glass but is pretty abrasion resistant and is good for high wear areas like stems and sharp chines. Dynel is nothing like Kevlar. Dynel is a copoylmer material and is basically an acrylic whereas Kevlar is an aramid. Dynel has very different working properties than aramid. It cuts much more easily and soaks up a good bit more resin as well. Dynel is rather slippery when subjected to abrasion whereas aramid tends to "fuzz up".

pblanc wrote:
I have also used a good bit of Dynel (5 oz/sq yd). It is not as strong as S 'glass but is pretty abrasion resistant and is good for high wear areas like stems and sharp chines. Dynel is nothing like Kevlar. Dynel is a copoylmer material and is basically an acrylic whereas Kevlar is an aramid. Dynel has very different working properties than aramid. It cuts much more easily and soaks up a good bit more resin as well. Dynel is rather slippery when subjected to abrasion whereas aramid tends to "fuzz up".

i think i forgot to mention it is the first and only repair i've done lol. thanks for the details, that makes a lot of sense. it takes a ton of resin to soak it for sure. i had a separated seam on the stern of my c1 slalom and i did a dynel layer wrapped over from the bottom and then top so that they overlapped the seam. then i put s-glass over the two dynel areas and then lastly i went with a diolen seam tape layer over all that. it is now water tight although i got slightly messy so it kind of looks crappy, no noticeable decrease in performance though!

When I do a repair, the last "layer" I apply is Handi-Wrap over (and well past) the still-wet repair area. I use wide masking tape to stretch the film tight against the layup. I can then use a roller to work the area smooth and void-free.

Kevlar cuts fine with new scissors. I have a pair that are ONLY used for Kevlar (once you use them for glass they won't work well on Kevlar); I've had them for a number of projects / boats and they are going strong.

Dynel is wicked stuff. Apart from soaking up an amazing amount of resin the stuff is brutal on metal blades. I made a Maven with Dynel as the outer layer of the hull. Cutting it down (cured) I usually get the hull and deck out of one blade, sometimes more. I went through 4 blades just cutting the hull!

jaywolfe wrote:ask her about dynel as a repair option, it's basically a cheaper kevlar that can't be called kevlar due to trade mark infringement.

You mean TWARON, Not dynel. Dynel is a resin sponge, but does a great job as wear plates for heavy wear areas... TWARON is Aramid - just like kevlar... Typically it should be used under a glass layer, but probably does not matter for small patches that are not going to be cosmetically matched.

Kevlar or TWARON do not sand smoothly - both fuzz when abraded, glass - both E and S sand smoothly and are better for the outside of a cosmetic patch.

No, he meant diolen, not Dynel or Twaron. Twaron is not a cheaper alternative to Kevlar. It is not a weaker alternative to Kevlar. Diolen is CAP or polyester, and is a cheaper, though weaker, alternative to Kevlar. This info is available on the sweetcomposites website.