A while back, I posted about these fins I am making out Guadua, a type of bamboo, and I’d like to get a better idea of where i should go next. I cut the guadua lengthwise at 30degree angles and alternately glued them together with wood glue. Once it dried in this clamp setup I made to keep it tight and strong, I planed the whole sheet down and I cut out the rough fin shape and then proceeded to sand the fins to the shape and foil I wanted for each fin. Each fin has the wood attatched horizontally up and down the fin, so its like blocks stacked one on the other.
At this point, I’m not sure if I should glass the fins or just coat the fins in resin; if I should increase weight and width or sacrifice strength?
Plus, as I’m making only two (permanent) side fins on an 8’0 board, I’m also in a quandry as to how and where I should position the fins; how far from the tail, toe-in angles, fin cant, etc.
I’m really in need of some help here, as most people I’ve talked to about this part don’t deal with fins. Thanks.
I'm not a wood working expert and your answers might come more accurately from some of the companies that specialize in bamboo surfboards. But, as I recall, wood glue is water soluable. Epoxy may have been a better binder. Since you've laid up a series of veneers strips, you want to make sure that when they experience torsional flex the binder will not shear. For this reason with water soluable wood glue as your current binder, I would strongly recommend encasing your core in a fiberglass shell. The schedule of laminate will depend on how much flex your structure is planned to resist.
Mix up a “slow” mix of resin and catalyst (no wax) and brush it on your fin to seal it. When it’s dry look for any flat areas on the wood where the resin is not glossy and coat it again until all the wood is glossed with a coat of resin. This will seal it and make it ready for glassing. As a furniture maker, I make quite a few wood skegs (fins) and have found that some woods like burled redwood require up to four coats to properly seal, while straight grained redwood and other hardwoods seal up with just one coat. You’re likely to get delamination of the glass if they are not sealed. Never used bamboo, but would guess it will seal easily.
You are the artist, but as an old-school guy I find myself wanting to see your glued up sections running vertical up and down the fin as they all were in the day (still are) instead of horizontal as you mentioned. You mentioned ripping them at 30 degrees…do you get much contrasting color in the bamboo?
Some of the other guys can post recommendations about setting your fins, cant, etc. (I’m a single skeg guy). Sounds like you’re on the right track. Enjoy the ride!
Epoxy glue can actually become brittle with age and heat cycles. A wood glue such as Titebond (Titebond II is water resistant) or a Gorilla glue type adhesive is fine and will take moderate flex and expansion/contraction. The fin will be glassed and therefore watertight any way, so the glue is not much of an issue. Whether it’s viewed good or bad, unless the bamboo fin is super thin, once glassed with a couple layers of 6oz (recommended) it isn’t going to flex much.
Thanks for the help! I knew wood glue wouldn’t be as strong as epoxy for example, but it would have been much more difficult to get the finer work done on the fin with layers of epoxy sandwhiched between the wood for sanding (had some experience with that in some early models), and i had planned to somehow resin/glass the fin. I went with the suggestion to coat the fin in resin first, and then see about putting a lam coat on it. The fins aren’t super thing fins at all, they’re kinda wide but foiled for left and right sides, and I had heard mentioned before that wood needs to be sealed before being glassed. They have one coat now, and seem to be well sealed as they’re a very straight-grained wood. And I hadn’t thought about running the pieces vertically before, thinking if it ever were to snap, it would be a cleaner snap if they went horizonatlly rather than ripping through the board. I don’t think this was the most intelligent way to go about it, thinking reactivly as opposed to proactively, but the fins do look really good if nothing else. With the 30degree rips and alternating strips, you can really see the contratsing colors of the wood, and it looks great, a really nice natural wood finish.
After i sand the resin coat a bit, I’m thinking about adding two lam coats to both sides, unless anyone recommends more/less? I’ll get some pictures of the fins and the board up asap. Thanks a whole lot.
you have to use fabric ,dont just use resin , when you surf the amount of load on the fins is huge , they will crack up and get water logged if you just paint some resin on them…
IMHO if you want your wooden fins the hold up and perform well. There should be a spine in the center of symmetrically foiled fin of at least 5 layers of epoxy stacked 6oz fiberglass. On asymmetrically foiled fins it’ll be on the high pressure side. When ever you laminate layers of wood together it should be done with at least one layer of glass in the sandwich. After foiling the fin you’ll be well advised to laminate at least one layer of 4oz. (two would be better) with epoxy over the finished product along with an epoxy hot coat. You can shoot the epoxy hotcoat while the final lamination is still going off and when the whole thing is cured you can block sand the fin to true everything up and wet sand down to 1200 grit or finner to get a perfect finish product.
Bottom line polyester and wood is a bad mix IMHO simply because the bond one gets between the two is very poor.
You may have finished your fins by now, but I’ve been away from any computer for the last several days, so I’ll respond to the last few posts regarding your bamboo fins. First, yea you have to cloth glass your fins. I use two or three layers of 6oz over my wood fins. Contrary to the other response I have never used epoxy on any of my wood skegs. Thousands of the beautiful old 60s laminated wood skegs survive today with nary a trace of epoxy. It’s true that poly resin is not a magnet to wood, but there are many wood boards out there being crafted with poly resin (I have done a few myself, and Professor J. Phillips can attest to dozens of dozens).
You just have to seal them first before glassing them, which is why I went on in my previous post about sealing enough to “get it right” before glassing them.
Sooo, seal them good, glass them with a few layers of cloth and resin for strength, and enjoy your beautiful skegs! Enjoy the ride.