Seeking advice for fixing swollen stringer at finbox.

[SDSG]

Good day Swaylockians!!  Just finished my first board, and this is my first post here. What an amazing community!  I’d have been kinda lost without the content on this forum, so huge thanks to everyone that has contributed and helped us newbies out on our first build.   

The board in question is a 9’2” longboard, using standard density US Blank PU foam core, and PE resin.  The stringer is ¼ inch wide and I believe it’s basswood.  2 layers of 6 oz glass on the deck, and one layer of 6 oz on the bottom, plus another layer of 6 oz. (fin patch) from the tail to about 1 foot in front of the fin box.  Did the lamination with a seafoam green tint.  The board was finished last weekend.  After just two brief surf sessions, tonight I noticed the stringer seems to have swelled right in front of the finbox, causing the edge of fiberglass to break away from the edge of the finbox as you can see in the photo.  Some searching in this forum has me convinced this is in fact caused by water getting in there and causing the stringer to swell.   

I’m wondering if you more experienced builders agree this looks like a problem caused by the stringer swelling, and if so, what would you recommend for the fix?  Since the board is brand new, I’d love to fix in in a way that doesn’t ruin that shiny new look if possible

I’ve read that water can seep along the stringer, so right now the board is resting tail down so that at least gravity will not encourage water to travel any further towards the nose than it already has. While it’s just the first inch or two of the stringer in front of the finbox that’s really raised (seems to be almost ⅛ of an inch)  I feel a slight bump along the stringer up to about 8 inches forward of the finbox.   

In case it helps here’s some details on the install of the fin box. Before the board got wet, the area in front of the finbox was smooth and flush with the surface of the finbox.  The box was installed after the hot coat, using laminating resin mixed with some cabosil and a bit of white pigment, and I also used a piece of 6 oz. glass for reinforcement all around the inside of the finbox hole.  The hole for the box was a bit larger than needed due to some routing mistakes, but not too bad.   I did not do a glass patch over the finbox (now I wish I had). The gloss coat did bridge the edge where the finbox meets the board surface because I taped off the box so as to just barely cover the slot in the box.  

Thanks in advance for any and all comments and help!

[doc]

Ohhhkay, you do have a problem and you have the cause nailed. The stringer is indeed taking up water and ‘growing’. taking the path of least resistance. The lighter the wood, the more it’s prone to doing that, balsa being particularly infamous in that respect. And yes, you do get moisture travelling along in the wood, capillary action or whatever. This is why you see boards going brown along the stringer, water gets in throgh a tiny leak, gets sucked along and reacts with the foam and sunlight and there ya go.

And this is particularly a bummer because you really did it right, fin patch, glass in the fin box hole and so forth. In hindsight, had you tied the glass in the box into the bottom glass and the fin patch, that would have encapsulated the wood better and so forth, you might not have had this problem… But the white pigment in the filler around the box kinda made that impossible. Hindsight is overrated. And I’m kinda surprised the resin/glass/cloth in the fin box didn’t seal it better.

Neat. What are you gonna do? As my old Ethics professor used to say, ‘That depends…’ How long are you willing to wait and how involved do you want to get? 

If, say, you wanted to leave the board vertical, in a very dry place with some very gentle heat like a 25 watt bulb or similar, you can dry it out to some extent. But we are talking months. Then, sand it flat-ish, inject something like thin/low viscosity ‘penetrating’ epoxy to impregnate and stabilise foam and wood right where it’s open/leaking now, add glass to seal. That’s going to get it down some, not all, you will still have some brown foam and maybe browned stringer in the area someday.

Option B, same thing, same methods, but only let it dry for a week or so.  Wood will go down less, you’re gonna have more water stain/brown  to wood and foam, the epoxy ( if you use it, it’s optional with this option)  probably won’t penetrate as well, but it is quicker.

What I wouldn’t do: hit it with a heat gun or similar to try and power-dry the stringer and foam.  You’re never going to dry it out or shrink it completely, no matter what you do. And that much heat is likely to make delaminations, now or later.

Likewise getting surgical, cutting out glass and planing down the stringer and other similar stuff, maybe somebody thinks they could do that up so it wouldn’t show, but I really don’t think I could.

Likewise putting a small hole in there and putting a vaccum pump on it to suck out the water, nice tech idea but unforeseen consequences are likely.,  

What would I do? Probably Option B, stabilise it, seal it, strengthen it a little and surf the hell out of said board. The good news, or as good as it gets, is you caught it early and not six months down the line when you’d get water dripping out. You’ll still have a good, strong, usable board for a fairly long time.

One more thing- have a look at the back of the finbox. Any reinforcements you add to the front, do 'em at the back too. Might not need it, but you’re doing the front anyhow. 

Leastwise, that’s my take on it.  I’m sure there will be others. The thin penetrating epoxy, you want something similar to https://www.rotdoctor.com/epoxy/woodrestoration.html, there’s quite a few brands out there, made for bringing back rotted wood… 

hope that’s of some use

doc…

 

[SDSG]

Doc, thank you for such a detailed reply and laying out some options.  Who would have thought your ethics professor would be chiming in on surfboard repair :)  Already the swelling has diminished a bit, so i guess that’s a good sign.  I will wait a bit and see if this trend continues and use that knowledge to decide how I will proceed.  While I don’t want to get surgical, I do have a very thin rotary blade for my dremel that I could use to cut some slits and peel back a one inch wide strip of the glass, let’s say about 12 inches long in front of the fin box.  I figure that would accelerate the drying and reduce the seepage of moisture further into the stringer.  I could just cut two lines, one on each side of stringer, and then kind of peel it back from the finbox, but not break it away from the board completely.  Then when it’s all dry, and perhaps I’d have to shave the stringer a bit, I’d just let that glass strip fall back into place with some laminating resin.  In this case I’d just extend the fin patch over this strip as well as around the finbox.  We shall see.  Tough for my son and I not to be surfing this thing after all the hard work to get to this point, and the excitement of riding a board we built! 

[doc]

Now, that particular philosophy professor had been an offshore fisherman, truck driver, blacksmith, semi-pro boxer and at the time still did a little bartending, Still going strong too, teaching philosophy and tech writing. He and I got along and he’d prolly be absolutely tickled by being cited concerning something practical. 

Anyhow- see, what you’re talking about is precisely what I meant by surgical. I know you want to get it done and get back out- this is in many ways echoing the disputes internists and surgeons have. When dealing with the same issues, you are gonna have additional surgical risks of screwing things up a lot worse, it will leave scars and your final outcome will be pretty much the same as those of going at it gently.

F’rinstance, lets say you do what’s effectively a second fin patch around and to the box, good idea. But by the time you do that, you have a little buildup and it’ll pretty much mask your stringer bulge, making surgery unneccessary. .

In any case, you’re not gonna dry it out completely. And by the time you pull off the glass, with the foam that sticks to it, likely some wood too, put it back, glass to make up for the strength that went away with the cut…you see where this is going? 

Back to my philosophy professor. He was and remains a Platonist, big into the idea that while there may be the ideal of perfection, we live in an imperfect world. Shadows on the wall of the cave as Plato put it. The prof, he wrote a book about it. Still in print too.

In the same way, you’re not gonna get a perfect job, a perfect repair. It’s not possible in our imperfect world.

Shoot for ‘pretty damned good’ .

hope that’s of use

doc… 

[McDing]

If you do effectively remove the glass over the stringer, you will then be able to level the stringer with a mini-plane.  You will have to sand an area of the glass to insure adhesion.  I would try to cut a strip the width of the stringer and remove that glass strip.  Then let it dry a few days. Mini-plane the stringer down at least to flush with surrounding glass.  If possible even a bit below the glass.  Then put a patch over it.  You should be able to maintain your resin tint by doing it the way I have described.  Of course you will have to hotcoat, sand, gloss and polish to match.

[SDSG]

Doc, I’m liking the philosphical ramblings, and your insights are super helpful and appreciated. 

McDing, thank you for the advice.  If I go for surgery I think I’ll do it as you suggest instead of my original idea of a wider strip of glass removed. 

This morning the swelling has not diminished relative to where it was yesterday morning, so it may be approaching the flatter part of that curve.

 

[SDSG]

On the home stretch with this repair and very pleased with how it’s going. In case some details of my process may help someone in the future, here’s what I did.  I decided to cut out a piece the fiberglass in front of the finbox, just as wide as the stringer and about 6 inches long, so from the finbox to about 6 inches ahead of the finbox.  I let the stringer dry that way for a week.  I then used some chisels and the edge of a mini flat file to sand down the stringer to aprox it’s original thickness.  I used one layer of 6 oz cloth about 3 inches wide running from about 2 inches behind the finbox to about 8 inches ahead of the finbox. I taped off the area in question, a bit smaller than the glass patch, then scuffed up the surface with 100 grit.  When I did that lamination, first filled the bare stringer area with resin, placed the glass strip I had cut off back in place, and then the glass patch on top of that.   I saturated the glass cloth with sanding resin while on wax paper, then simply picked it up and placed it in the desired area. I did not tape the finbox slot.  Once the resin gelled, i cut the cloth at the tape line with a single edge razor, and then removed the tape.  Seemed to be a good lamination, very uniform in terms of saturation.   After 24 hours, I sanded the edges of the glass a bit for a smoother transition, as well as the entire glass patch to get rid of the shiny surface.  Then placed new tape about 1/2 inch wider than last time all around, taped over only the slot area of the finbox, and applied a hot coat.  then sanded that with 120, 150, then 220, and applied gloss coat.   Now I just need to let it dry and sand the edges to create a smooth transition to the existing surface. Then I plan to sand through the grits up to about 1000 then polish with #2 surboard polish, which is what I used on the rest of the board.  Hopefully it will barely show.   A few pics help tell the story.  Thanks again Doc and McDing for your help and advice!!!  Should be back in the water in a few days. 

[McDing]

Good job.  That’s the way I would have done it.  Saved everything and barely noticeable.  Even when I do large delams, I will glue the old glass back down if possible.  Lowel