Almost broken, grooves on the bottom

I rode my almost brand new 9’1 into a closeout and as a result it’s bottom got 4 one finger wide, about 1 mm deep grooves that start from the edge and end just before to the stringer. The grooves are not continuous from edge to edge, but rather go to the stringer and continue from a place about 2" up or down the stringer to the opposite edge. There are no visible cracks anywhere. Also the stringer seems to be in a perfect condition.

Friend if mine told that the board has bent, but not broken, and the laminate has compressed which has caused the grooves. What should be done: just sanding & filling so that the grooves disappear? Or should thre be added an extra cloth to support the damaged area?

The board is a lightweight ‘high performance’, it’s thin (2 3/4 ") and has very thin rails.

Same thing happened to me a few months ago. I posted here- Skinning Delam Board -about how I fixed the problem. My board had the same ‘wrinkles’ from rail to stringer and it wiggled when I applied pressure up (deck ward) and down.

Sorry, hope this helps.


If it was just flexed (not permanently bent), the repair is fairly easy. If it is bent, you need to release the cloth (cut or grind it away) on both sides until it straightens. You may need to apply weight or clamp it until the original rocker is back (do this carefully). Either way, you need to laminate a couple of layers of cloth on both sides of the flexed area. Grind the grooves out with 80 grit, don’t hit the foam or you’ll need filler. Prep sand an area 8-10" wider on each side from where the grooves were. Turn it over and prep sand the same width on the deckside. Use two layers of cloth, the inner one about 4" less in width than the outer one and as wide as the rail (like a deck patch). Cut the outermost layer so it has a radius (inward or outward) or an triangle at both ends. You don’t want a straight line in the cloth perpendicular to the stringer. Tape off the area smaller than the outer cloth including a cutlap on the opposite side. Laminate, cut the cloth to the tape edges and repeat for the otherside. Hotcoat, feather the edges and gloss.

Thanks for the advise. Gave it a closer look. There are some very small cracks on the edges of the “crease”, but the deck is in perfect condition and the rocker is continuous, no bent spots. I suppose I need nothing on the deck side since no damage is visible? The damage seems to be smaller than in examples you described, so I still need multiple layers or is just one cloth enough? If I use just one cloth, how wide should it be? Thanks.

Onshore, you asked “how wide should it be?” Let me take a shot at that.

Think of what the width does: it affords bonding area. You have to have enough bond area on either side of the crack to take full advantage of the tensile strength that the glass is going to provide. More layers of glass, more bonding area. A patch won’t do any good if it pulls off, intact, due to the glass being stronger in tension than the bond strength of the area.

As an engineer (though a civil, not a structural) concrete reinforcement design is just the same way: two rebars must be lapped 40 diameters. The rebar has to be embedded a certain minimum depth. Rebar ends are often bent into a hook. Rebars have a ridged/patterned/deformed surface to they resist axial pullout. Same concept in each case. However, concrete design is much more formalized and has set requirements and a code, while surfboard glassing certainly does not.

Now, I expect you want the easy answer, “X inches”. X depends on the prep you’re gonna do, but I’d speculate that with a good 60 grit sanding, for 6 ounce glass, a minimum would be, um, say, 4 inches on each side of the crack. Wider patch would also be a little easier to feather in.

Hope this helps.

I was told that gelcoat is a good alternative to polyester resin, if I want the resin to be white instead of transparent. What about epoxy with pigment, any reason for using it instead?