On Thursday we cut the holes for 10.5" fin box through a single layer of 6 oz cloth with epoxy resin, painted the inside of the hole with a generous amount of resin, pooled a bit in the bottom, painted the fin box, wrapped it in a piece of 6 oz cloth wetted with resin, pushed it into the hole until it was flush and the excess resin oozed up, left the wet excess cloth sticking up, left it to dry. Friday trimmed off the excess cloth and ground down the top of the box with a variable speed sander, prepped the board, taped the hole in the box, did a gloss coat that is now dry and just needs final sand and polish. Did not use any fin patch or extra strips of cloth around the box. My omission and lack of research. Is there a potential weakness here? What is the possiblity of cracking? Or is the epoxy strong enough? If not what solution without messing up these guys nicely finished boards? Due to do the deck gloss coat this morning.
I think you already know what the risk is here. The likelyhood of damage if it hits a rock or run up onto the sand is much greater. It will also fatigue faster over time, depending on how it’s ridden and the size fin used. You could just leave it as is and end up doing a repair at some point. Or… yep… sand it down to the weave, lay a cloth patch over the box (you don’t even really have to tape it if you’re careful laminating it and don’t force resin down into the opening of the box). Fair the edge, and re-hot/gloss the area. If you’re like me, you might end up with a halo around the area that was re-glossed, but the pros can do it pretty cleanly.
Thanks for this nj. We did the deck gloss coat this morning and have completely run out of resin. I told the guys about the consequences of my oversight. They are happy to leave things as they are but I’ll be ordering some more resin for a new board I’m starting so it might be worth while to follow your advice. Better to have a halo that a cracked or loose finbox eventually in which case my halo is going to tarnished. Lots of lessons learnt on this project.
"Standard" finbox installations don't have glass over patches but they're a good idea. Most glassers skip it or charge extra to do it.
The main issue with finboxes installed in single stringer boards is that the stringer integrity is almost completely violated when the routing is accomplished. A glassover patch might help right at the front of the finbox which is a notorious spot for cracks or even snapping the whole tail off.
Picture a side view of your stringer after the box hole is routed out.
PS - those boards look great for their intended purpose.
How do you do the glass patch over the box after it’s been sanding flush to the board? What do you use to cover the slot?
I’m doing stringerless EPS with long single fin boxes. Have not done a glass patch over the box after it’s been sanded down, and the patches that were done over the boxes, usually get sanded down to be flush with the bottom lam.
I like to use the open slot boxes, but we use the ones that are sealed too. I only use glass under and around the box when I install the box with a thickened resin slurry for the open boxes.
Capping the box is always a good idea for strength. However it is true, a lot of production boards do not get capped. Tape over the box hole and cut it really close to the hole with a blade. This way the hole will be covered and about half an inch of the box is left in the open. Lay a layer of six out over the entire box and laminate. During mid-gel cut around the edge of the tape and remove the glass/tape-done.
Proceed to hotcoat as usual-just don’t get resin down the fin hole. I like to put tape inside the box so resin can’t sneak in when painting it on.
Howzit love, I never cap boxes and only put a layer of 6 oz in the bottom and not even the sides but I do punch 1/4" holes on both sides of the stringer at the front an he back of the hole so when I fill and set the box the resin and milled fibers flow into the holes and it does help strengthen the install some, Just something I decid to try and kept doing it to see if it would stop the fractures at the front of the box and it did. Aloha,Kokua
I do a cap over the box and 6 oz cloth in the hole. I did not get that far in the thread. If you want I'll post the rest here. John Mellor does a really cool trick for long board boxes. I was hoping to get some ideas to make my installs better. I want to do a better /stronger fin box. Most longboards at my local beach have stress cracks at the front of the box. I think we can work together to find a good solution......
Yes, do post the rest here. Sorry I missed the thread at first, good topic and accompanying pictorial.
McDing told me about the layer of glass between foam and box. Then, I put a second layer over the box. You can see the double glass in the tail area. I don't recall on this one, but I think since I tinted the 2nd layer also, I had to repaint the fin box white afterwards, before gloss. (I know I did that on the green board, so I must have done it on this one too)
On wood boards, I just epoxy (glue) the box in, it tends to be very strong. Whole different animal, those. Although I do generally like to get some glass to "cap" the box, even on those.
I did a completely hollow board (the green one) where just glueing it to the 3/16" plywood skin wasn't enough, had some stress cracks after just a little use, so I went back and reinforced the fin box and tail area with dowels.
How did you define the outline of the diamond shaped patch?
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I masked off the diamond shape, then cut with a razor after the resin gelled, and pulled the tape. I added the line with paint. Because I tinted the diamond, I had to go back and paint the box white, before glossing. Don't know if I recommend any of that, but I do feel better when the fin box has a bit of glass over it. Masked the box with 1/2" tape to cover the slot while glassing.
When I sanded prior to glossing, I sanded through just a bit on my painted line. It looks OK. None of my boards are perfect!
Here's a Bruce Jones trick... the mini-stringers on either side of the box might be redundant since the board already has two stringers. I cut sideways slots inside the box hole under the glass so the resin makes contact with the wood.
I've had boxes blow out sideways - on a pro-glassed Skip Frye longboard. I've also broken off tails after hitting a rock. Other than that, I'm not naming names.
The new Future single box is another solution, installs under lam and the design spreads loads well. I borrowed these pics (originally posted by atomized) from a thread in ''industry talk".
The nice thing about the open slot boxes is having the ability to make sure the fin is perpendicular to the board. I’ve done the tape over thing but I always end up with a little lip where the tape was. I usually don’t do gloss coats, just spray poly or acrylic over the sanded epoxy.
I guess I could use tape more creatively and do a gloss coat if I want to get it perfect. Nah… too much work.
Howzit stingray, try my trick with the holes on both sides of the stringer at both ends half way down the box router hole, but you have to use milled fibers to help for strength,it works and easy with no capping. Aloha,Kokua
