My board has an eight inch crack where the bottom has separated from the top of the board along the rail. I am planning on using marine JB weld and clamps to hold it in place while it dries. If you have dealt with this type of fix before and have pointers let me know.

Chris, using JB weld will not work. It will seal for a while, but the first good flex, it will crack and you're back where you started. Mistral has a couple different constructions, some of which use an HDPE shell around the board that is fused at the seam. This is what some call a "plastic" board, because it feels like they're made of plastic. In actuallity, the plastic shell is only as thick as a the plastic in a milk jug (very thin). Either way, what you need to do, is cut back about 2" from either side of the crack, and 2" past each end. You would need to route an area about 2 mm deep, so that when you laminate fiber glass in this space it matches back to the original surface. You should laminate with "S" glass and epoxy. If you don't have supplies, then you can get them from US Composites (best and least expensive: www.uscomposites.com). After you have laminated over the crack, you need to add layers of epoxy or some type of faring compound (Bondo will work, but it's not very strong) and sand it to match the hull profile. Then paint it when done. finished. You can find more help at www.boardlady.com

Hi Chris,

I am certainly no expert, but I have handled repairs similar to this on in the past. My initial response would be to steer you away from just using Marine JB weld and clamps. Here's my recommendation:

1) read-up on repairs--this is the most helpful site I could find: boardlady.com/repairmenu.htm
2) I would then sand/grind off all of the damaged material (outer layers of fiberglass, Divinycell, and any foam core that is loose or damaged. Unless it is uncracked and firmly attached, it needs to be sanded off. Your board is a sandwich construction, which means its construction is outer layers of glass, divinycell, inner layers of glass, then foam core. Best case would be to have the glass/divinycell/glass "sandwich" separated from an undamaged core. However, my guess is that you most likely have a bit of damage to your core as well.
3) As detailed by the Board Lady, the ultimate goal is to replace each layer with a similar material so that your board does not develop any stress risers as it flexes.
4) If you need to replace the core, I have had luck using a two-part polyurethane to rebuild the core. This is a bit of a pain. I created a crude form using saran wrap and duct tape, added the two-part polyurethane mix, and then sanded it to shape. It was super messy and you want to make sure that the polyurethane does not have any voids--and that it is firmly attached to the "good" core material. It may be tempting to just use epoxy, but epoxy is much stiffer than the foam core material and will lead to stress cracks over time.
5) Once the polyurethane core is sanded to shape, you can glass this as you would any other repair:

-cut your pieces of fiberglass and/or carbon to be a bit larger than your repair area
-lay them up at angles so that the fibers are running in different directions
-wet out the fiberglass/carbon with a two-part epoxy (I use west systems epoxy with the slow hardner)
-use a squeegy to force out as much resin from laminate as possible--keep going until you can see the texture of the fiberglass
-professionals would use a vacuum set-up. I don't have a vacuum pump, so I use saran wrap or other plastic material and duct tape/strapping tape to apply pressure to the laminate while it cures. You want to make sure everything is pressed firmly together and that none of the pieces of glass/carbon are floating on a layer epoxy
-let it cure and then sand to feather the repair into the existing fiberglass
-add fairing compound (silica microbubbles, etc.) to expoxy, apply to fiberglass and sand until the surface is level--I sometimes skip this step depending upon my motivation....
-paint (If you don't use a fairing compound, it will take much more paint to cover)

If the damage is relatively shallow, but still into the core, I have done something like this with success in the past: boardlady.com/wipeout.htm (essentially creating a thick divinycell sandwhich to repair the damaged area)

JB weld or any other epoxy does not provide any structural strength--the fiber material in the composite, such as fiberglass/carbon/kevlar/etc. provides all the strength. To be a strong repair, you really need to repair the fiberglass and in order to be strong, the fiberglass need to be attached to undamaged material.

Regarding tools, I use a 90 degree drill with a foam sanding pad and various grits of sandpaper--I have found this give me better control than using a standard drill.

Let me know if you have any questions. I can post a few pictures next week when I have a better internet connection.


I hope this helps!

Thanks for the pointers, seems I have a job cut out for me. Here is what I am looking at, "lay them up at angles so that the fibers are running in different directions", not sure about how to do that instruction as it's on the edge of the board. I could see making a rectangle being two inches on either side down to the fiber glass and then put the fiberglass in the area. In this case it would be two inches on the bottom and two inches on the side and have to rap around the rail. The fiber glass on the bottom seems to be like an eighth of an inch thick with a then coat of what Jake is calling divinycell. Checkout the picture.

I'm not sure if you are still looking for additional feedback, but as Eric mentioned, you will need to first sand/route off all of the loose material (plastic, glass, divinycel, etc). I prefer to use a sander to ensure a long taper between the existing "good" glass and the glass used in the repaired area assuming that the outer layer is glass. The long taper allows the new glass to form a scarf joint with the old glass, which is stronger than the joint formed by "butting" the new glass up against the old glass end-to-end. Spend 30 minutes on the board lady's site and this will make more sense.

But, yes, you would need to sand both the rails and the bottom to remove all the damaged material and then lay the glass so that it drapes over both the rail and the bottom of the board. My comment regarding "lay them up at angles so that the fibers are running in different directions" means that if you use two layers of glass, the direction of the glass strands in the first layer should be rotated with respect to the glass strands in the second layer, etc.

Thank you, I will post pictures as I work my way though the repair. Going to get started on it this next week. I will check out the board lady's site, I appreciate all the advice!

I decided to fix the board in the least expensive manner and in a simple way that someone like me with no board repair skills could pull off. I used spray foam and Marine-tex.







I sanded around the edges of the crack both on the outside and inside. I removed all the loose foam from inside the board. I sprayed the foam inside the gap between the board foam and bottom sheet of fiberglass where it separated. I then put Marine-tex inside covering where there were cracks and filled the main crack with Marine-tex.




I used particle board, clamps and weights to apply pressure to the board and hold it together while the Marine-tex and foam was drying.




Then I sanded down the Marine-tex and then applied another thin coat to the bottom of the board to make the surface level on the edge where I had made the repair. Then I spray painted to mask the ugliness of the repair.

I know this is no Greg from Sheb. fix but it is the best someone like me can pull off, It didn't take a lot of time and money and seems to be a strong patch. I will see how well it holds.

Dunno if you're in Chicago, but if so I'd happily does out some epoxy, fillers and cloth if you end up needing it.

Thanks, sorry, fillers and cloth? Did I miss a step? I have one more board to fix which is the exact same make and model board and broke in the same manner. I did this one first as an experiment. The other board has sentimental value.

I have no real experience fixing boards, but often times if the outer laminate is damaged you need to replace it with structural bits. Can't say one way or another how that will hold up, but if it goes I think perhaps grinding a beveled area around the repair, then a few layers of fiberglass cloth in staggered sizes bridging the crack would be a forever fix, then covered up with structural filler mixed in with epoxy and then finished. Was also just saying if anyone needs small amounts of epoxy and glass supplies I have some limited stuff at my shop and would happily cut off bits/fill some small jars with epoxy so people don't have to buy 40yds of cloth.