I returned from a surf yesterday to discover a couple of fairly long gloss coat cracks radiating from the front of the fin box. My board is a 9’2 longboard in polyester and I would like some advice on the best way to fix these cracks if indeed I need to.
I have done a couple of searches and the advice seems to vary from using a dremel to create a ‘trench’ and then filling with hot coat at one end of the scale, to those who advocate full surgery!
The resin swirl is pretty important to me as I shaped and glassed the board myself - I would like to avoid having to remove it if possible.
The cracks don’t yield to presseure and can just about be felt when you run your fingernail perpendicular to them.
I’ve had this problem before from clipping a reef. Once this area is compromised, it stays that way. No matter what the glass patch is. IF the glass was fractured, the only solution that lasted was what Mr. Mellor said installing “strong backs” along side the fin box. In the past, I used lexan plastic and extended them twice the length of the box towards the nose. I recessed them a bit and hid them with pigment. The board lasted another 7-8 months until it got too big for the repair to stand up to. If I were to do it again, I’d follow a lot of what “lockbox” spelled out with strong backs.
Huck, you can see that is the weakest spot on the entire board. Another layer of glass would have to be fairly large. You are a builder, think of the cantilever equation: bearing equals twice the overhang.Think pre or post tension cables. Longboards weren’t made to surf like a shortboard or a skateboard, not that they couldn’t be…but “crack happens”. I’d take a razor knife and widen the crack minimally and fill then polish. Next I’d order another blank.
This is a classic case of why all fin boxes should be capped IMO. I'm sure I'll get opposition here..but don't care really. I have nearly 20 years experience repairing this type of damage and have learned how to avoid it. This is a very common problem that I fix more often times than I care to keep track of. And it's not just in the gloss those cracks go right down into the lamination. Keep surfing it and you better hope you don't hit bottom or get a wave land on your tail or you gonna have two surfboards all of the sudden. I do find it interesting however that even with the new style (FCS I think) longboard box..with rounded ends..the problem still occurs. Rounding edges and corners definately helps minimize cracks forming..but doesn't eliminate them..obviously, as pictured here.
The most common cause for this type of stress crack is beaching the board with a large sized fin in the box. It's leveraged from the fin contacting the sand or some other solid object. Not from doing airs lol. It is caused due to the fact that you have a deep hole routed out which removes a large portion of the stringer. This creates a weak point due to there being a joint there where you have a box glued in with resin with no cap to make the joint as ONE. If it were capped most likely that jolt that occured would have reverberated into the stringer where it would have been absorbed. When a serious stress occurs like impacting something this is the first place it shows up. The front of the box. Highly indicative of the fact that the board was moving forward at the time of impact. If the board was going backwards the crack would be at the back of the box. I never get this on my boards because anytime I install a long box (or any box for that matter) I cap it. Problem eliminated before it ever starts. Also why I will personally never have any type of fin box in my boards that isn't capped with glass.
It's a simple step that takes me about 30 seconds to do with suncure resin..then I sleep good. No worries ever having to come back and deal with trying to save a resin swirl that I worked so hard on.
If you would like to repair it properly..and permanently..here's what you do - Prepare the area to be glassed with fresh 60 grit paper and a medium or hard pad. Remove all of the hotcoat or as much as possible. If you'd like the repair to disappear..sand until you start seeing weave..but don't go through the glass into the color work. The crack will make itself even more visible as it fills with sanding dust while you prep it. This makes it easy to see where to prep to. In this case I would just do a butterfly on the whole tail starting from about 4 to 5 inches in front of those side plugs. Cap those too while your at it..and thank yourself later. Cut yourself a piece of 6 ounce glass that covers your whole prepped area. Tape off the cavity of the box as well as the cavities of those side plugs. Mix your lam resin but before applying it, take a brush and paint straight styrene over the cracks. They will disappear. While the styrene is still wet..apply the resin and glass. This seals the cracks from air drying the styrene out so that they stay invisible. Laminate your patch of glass and squeegee out all excess resin. Give it about 15 minutes after the lam resin has gelled then hotcoat it. As soon as the hotcoat has gelled take a brand new razor blade and cut open all your cavities before the glass gets too hard (major bitch later if you wait trust me). Now you can sand it..glosscoat it..and re-polish it. If you do it right you'll never know it happened. Good luck! Jim
Your explanation was more detailed than I ever could have given, but essentially is what I would have done if it were my board: sand the tail, and add an additional layer of glass over the whole tail area. Interesting observation about "capping" the box - by this I assume you mean a layer of glass over the box? Never have used styrene before, sounds like a good tip.
I think Bill missed the point about the board being 9' plus, hence the assumption it was from doing airs. I'm guessing he's seen similar damage from doing just that. I recently put a leash plug in just like you described - glass over it, and cut out the glass when it gels. Worked great, how I'll do 'em all from now on. And now that you've told me, I'll do the fin boxes that way too.
Hey Huck..imagine how much more fragile the area is when the box isn't mounted into the stringer. Capping over fin boxes is a load disperser. It moves any jolts away from the joint. Another thing I've found in regards to longboard boxes -they require a grinder to level them down. Or at least that's what most shops use. Grind into your glass a little around the "joint" with a worn out grinding disc.. and heat it up..and congrats..you just substantially weakened your box installation. Even FCS has moved to (or is moving towards) a flanged..glassed over fin box. What does that tell you?
Consider the fact that when the finbox was installed the integrity of the stringer was severely (like 80%-90%) compromised. A thin fiberglass cap might help some but IMO mini-stringers inserted on each side of the box would be the best solution. Once the mini-stringers are installed, the entire tail area of the bottom could be scuffed up and reglassed. Of particular note is that the finbox you installed has the Chinook-like outer edge supposedly designed to enhance finbox strength. Unfortunately, the weak spot is typically NOT around the edge of the box, rather directly in front of the box where the stringer was routed for the install. I've patched many boards that had trouble right there. I've also seen many that snapped in exactly that spot. A double stringered blank is one of the best prevention methods but for an after the fact fix, the mini-stringers work OK.
As noted later it is a longboard, and I am probably guilty of beaching the fin.
Seriously, thank you to everyone who has responded here, especially lokbox for your detailed explanation. It looks like I have a few sessions of hard graft on my hands. This board means a lot to me - it is the first i shaped, so I am keen to keep it in one piece and keep on surfing it too.
Just a question - I have seen styrene mentioned a couple of times - I assume this is not the wax in styrene that I am adding for gloss coat?
Styrene is one of the sovents in polyester resin. There is a certain % of it in the resin already. Not sure the exact amount because the state of california keeps changing the law and cutting it back. However you can buy gallons of it off of the truck and add however much you want..go figure. Many shops use it straight for wetting out any shatters on cut laps. Literally thinner than water..does a good job at making cracks disappear..if you can get it down into the cracks..and that depends on how well you prepped it.
If you use styrene make sure you follow the MSDS safety precautions -- its suposed to be some bad stuff...link from sways below.. Im sure there is more on the internet
I redid a finbox with a large 6oz tailpatch on an old LB. Worked great - barely covered the fin slot with tape and capped with glass. Its been good ever since. I remember reading somewhere here that some guys just glass over the open (un masked) slot and little or no resin will enter the box - However I was too chicken to try it.....
I’ve seen it done that way. As long as the weave is tight and you don’t lay on the squeegee too hard, very little resin bleeds through.
I prefer to play it safe and neat, though. Run a strip of 3/4" masking tape over the slot in the box. Do a generous fin patch on the tail. Cut away the glass at the edge of the tape right at the ‘gel’ stage.
And I also agree that the OP’s board was involved in some kind of impact to the front of the fin. Might have been a rock, or something else, but that is a very common repair I’ve done countless times.
If you wait much longer than 15 minutes it's gonna be difficult to trim the glass..but I agree it's better to wait a while before hotcoating. I do this with suncure..and have for years with no strength problems. 15 minutes in the bright sun is plenty cured to accept a hotcoat. Maybe with a UV lamp you might want to wait longer. Ideally you'd laminate your patch..and trim within a half hour. Then re-tape your cavities and then hotcoat a couple of hours later. 2 4ounce patches is good..if you get them on flat with no resin floated between the layers. Easier for the average guy to do 1 6 ounce...
I’m definately the average guy, so I will go for the single 6oz patch. I also live in the north of Scotland with only basic facilities and below average temps!
I am going to take the conservative route of minimal tape on the slot, cutting it clear just before the resin gels. I will then leave everything well alone before I leay down the resin coat.
Having read everyone’s input, I can visualise what needs to be done, and I am pretty confident of getting the job done to a satisfactory level.
Hardest part is the prep. Use a medium or hard pad and fresh 60 grit. Scrub/shave it until you see the weave start to show then let up on the pressure so you don't dig a deep hole or possibly go into the color/foam. It's pretty hard to get those types of cracks to disappear with the sander. You'll see the dust in the crack..and you'll keep going...sometimes too far so be careful. The fresh paper shaves off the hotcoat without heating it up. It's kinda like a one shot deal. Hotcoat comes right off then your into the weave a bit. THEN STOP! All you gotta remember is your just opening that crack enough to allow styrene to seap in. Prep the surrounding area evenly and flat to accept your patch of glass. Feather the trigger on the machine and just scrub it with the 60 grit. Level out more by hand with 60. Paint the styrene in and throw on the patch...
