Guys,
Yep - and I suppose we are saying that getting your wood nice and dry (below emc even, unless emc is below about 7% [where we start to loose strength]) before glassing is “a good thing” for a number of reasons.
-doug
getting back to wood fins … glassing them …[original question in the thread]…
is the moisture content in the wood in a small fin / keel going to be as large / critical an issue as with glassing big expanses of wood ? [ie: surfboard decks and rails and bottoms ] ?
What I mean is , has anybody here ever had a wood keel or fin delam ? [from moisture ?]. Just curious to know , as I’ve only had wood fins for around 2-3 years so far .
ben
Hey Chip,
Size doesn’t matter. Bottom line for this thread is to “seal” any wood, any size, any type, with resin before glassing.
yes … thanks for that confirmation , Richard !
On my earler fins , when I didn’t , I noticed lots of little …‘pinholes’ , I guess you’d call them .
So sealing with resin before glassing would also apply to glassing skateboard decks I assume …something I’ll probably be doing in the not too distant future , methinks !
ben
Hey Chip
on one of the sets of fins that I did recently (incidentally, the set that I hadn’t sealed first) I got a patch with lots of tiny bubbles… Did’nt actually click until just that this is probably the reason for it…DUH!
Jase (MMM)
To all who have contributed to this thread so far: thanks for all the good info. One question regarding pre-coating the wood with resin. Someone mentioned using a thinned coat of resin. Is the resin thinned with Styrene? Doug
chipfish61,
The thing that affects the speed MC changes most is thickness! A bit of wood a few mm thick will adjust to emc in a matter of hours. Safest bet for thin timber (like veneers for surfaces of fin cores) is to simply watrm it up and keep it warm for a few hours. The glass it while still warm.
Notice - I said warm not hot. It should a bit warmer than the surrounding air temperature… And not be blasted with hot, dry air 
-doug
Hey DougS!
I guess it depends on what you are sealing with. I am heading down the epoxy road, so… In any case I have always used something fairly thin for the sealing coat and squeegeed it into the timber. And not made the coat too thick.
Others might have quite a different opinion!
-doug
Styrene is nice with polyester, I guess, but acetone will work fine. Though I’d test it ( or any other thinner) for compatibility with any other adhesives you’re using.
hope that’s of use
doc…
Doc’s right, of course. Test, test and test again!
-doug
Aloha TJD
Just a warning from the trenches.
Wood fins look cool and are easy to make. But in larger surf they can have problems. Large waves can flex fins a lot and I have had wood fins delaminate in the middle of them being ridden.
I remember making a board for Gerry Lopez’s cousin that had a cool looking wooden/fiberglass fin. And right in the middle of a torqueing bottom turn on about an 8’+ wave at pipeline the fin split into two pieces both still attached to the board. The wipeout was not pretty and watching it happen was terrifying.
Interesting remark there Bill, do you think this has to do with the different flex of the resin vs. wood? I have been thinking about this problem and actually got some heavy fibers (carbon/aramide) to strengthen the wood fins.
Aloha Richard
I’ve always been interested in sealing my Balsa skins without increasing it’s weight and it looks like a thinned out concoction of epoxy acetone and denatured alcohol seems to what most use but I’ve been looking at the things that wood turners use to “harden” green wood before trying to turn them on lathe.
Any comments on the use of “green wood stabilizers” as a wood sealer to prevent such gassing during glassing?
From Woodcraft:
Quote:
Carving or turning green wood is certainly faster and easier than working with dry stock. But sometimes the extra work involved with slowly and carefully drying the wood to avoid checking hardly seems worth the trouble. Our greenwood sealers and stabilizers will control the drying speed as well as stabilize your wood.
Quote:
Pentacryl Wood Stabilizer
Carving or turning green wood is certainly faster and easier than working with dry stock. But sometimes the extra work involved with slowly and carefully drying the wood to avoid checking hardly seems worth the trouble. Not any more! Pentacryl is a revolutionary new product that combats the negative effects of drying by displacing water and moisture in the wood fibers. Your wood will dry quicker and more evenly, and the Pentacryl residue even lubricates your tools as you work. This non-toxic solution doesn’t stain the wood or affect finishing in any manner. The recommended method of application is total immersion, but the product can also be brushed or sprayed. Compared to the traditional wax coating method, you’ll find the drying time reduced by as much as 90% with Pentacryl! On average, a green 6" x 6" x 2" bowl blank would absorb 2 ounces of solution, be fully saturated in a week, and, if turned thin, dry in about three weeks.
also any idea about this stuff and whether it can be done with vaccum bag or it it can be purchased in sheets versus as pen blanks. I’ve been using this kind of stuff for nose and tail block material as a fin core it might be even better.
Quote:
Jumbo Staburlized® Pen Blanks
New jumbo pen blanks measure 7/8" x 7/8" x 5". Perfect for larger pen kits like our Cigar, El Grande or Robusto series, they can also be used with our regular kits. Each blank has been selected for extraordinary figure and then acrylic resin impregnated to make turning them easier. These blanks will add that special touch to your pens.
Stabilized or Impregnated Wood
Borderline or unstable wood, or even perfect wood, can be treated by stabilization. The wood is impregnated with epoxies and resins under high pressure and cured with heat. Color can be introduced during the process as well. Not all woods accept the process equally, and color penetration can vary throughout the blank based on hardness and grain pattern
Mahalo
wacth out for them fires…
PEG, (polyethlyne glycol) is a greenwood stabilizer commonly available. It replaces moisture in wood. Don’t know about its’ compatibility with poly or epoxy. Perhaps Richard can enlighten.
Quote:
Interesting remark there Bill, do you think this has to do with the different flex of the resin vs. wood? I have been thinking about this problem and actually got some heavy fibers (carbon/aramide) to strengthen the wood fins.
Aloha Dave
Yes it is the differrence in flex and the extent to which each material can flex before one tears away from the other. I have had similar problems with fabric layers in fins also.
Other than cosmetics, there is probably no good reason for including wood in a fin. Proper fin perfomance is governed by many forces and the more unpredictable nature of wood makes it unattractive for making performance fins.
Simply strengthening the fins may not be a good solution as fins that are too stiff and therefore unflexible in the right ways and places will create another whole set of problems.
Short unflexible fins like are commonly used on Fishes are probably fine done in wood but beyond that there are issues with wood. It isn’t by chance that the “standard” material for fins is layers of fiberglass. In the hands of a skilled designer and “foiler” pretty much all perfomance requirements for fins can be met.
But if cosmetics is a priority then making the fins look beautiful may override performance considerations. After all, how many people really ever surf waves that exceed their fins?
Aloha oneula,
Sorry, but I’ve had only very limited experience with “PEG”. Based on what little I do know, I would think though it would indeed dry and stabilize the wood, it, it might not necessarily do much if anything regarding an actual “seal”. As I’ve mentioned in the past, burled woods (especially redwood) seem to cause the most problems with “bubbling”. I have very little problems when using any other woods, especially when I mix the resin with about half the normal amount of catalyst for sealing. I use “casting resin” on my skegs to seal and to obtain the bead around the perimeter, as it’s easy to sand and cures crystal glass clear.
I’m interested in your mentioned concoction of epoxy, acetone, and alcohol. What is your recipe’? Any problems using poly resin glass over the epoxy sealed wood? Hope all is well!
Richard
Quote:
After all, how many people really ever surf waves that exceed their fins?
True!!
For me? I have yet to see that kind of condition. Still, better make a better fin…
Quote:
Quote:Interesting remark there Bill, do you think this has to do with the different flex of the resin vs. wood? I have been thinking about this problem and actually got some heavy fibers (carbon/aramide) to strengthen the wood fins.
…Other than cosmetics, there is probably no good reason for including wood in a fin. Proper fin perfomance is governed by many forces and the more unpredictable nature of wood makes it unattractive for making performance fins…
Aloha Bill,
I think some builders also wood in fins to help achieve positive buoyancy. I would humbly suggest that cold molding techniques (using veneer as thin as possible) might overcome the problems you have seen. While not strictly analogous, the stresses within (at least parts of) a cold molded boat hull at high speeds over time probably resemble those within a fin. On the other hand, while this can retain the cosmetics, there goes the buoyancy aspect. I think that gets filed under “no free lunch” :->
-Samiam
Hi, I’m pretty new to board building but I am a boatbuilder. From my experience (and certainly most manufacturer’s instructions in UK) thinning epoxy with acetone and alcohol is bad news. It appears that the thinning agents can get trapped between the wood and the cured epoxy. When the board gets warm the volatiles try to evaporate and cause the epoxy to debond from the wood.
The method I use is to warm the wood in the workshop and then warm it more in the area where the epoxy is being applied. I have also poured epoxy onto a low density wood (western red cedar) and then carefully warmed it with a hot air gun. This does 2 things. In warming the wood the air in the cells becomes less dense and rises, the epoxy becomes less viscous and is drawn deep into the cells to replace rising air.
This can leave bubbles on the surface but if the timing is right whilst the resin is still uncured light brushine with a fine paint brush will burst the bubbles and allow the resin to self level.
The alternative of course is to buy a specially formulated epoxy for wood penetration (WEST do a fantastic one). It is really thin and penetrates very deeply, I use it to prime plywood before glass sheathing.
Polyeaster does not really bond well to wood. Also polyesters tend to be brittle and flex differently from wood. Continuous flexing will result in the bond between the wood and the polyester breaking and delaminating.
Don’t know if this view is consistant with other peoples experience but I’d like to.
Great site this!!
Quote:
Aloha Bill,I think some builders also wood in fins to help achieve positive buoyancy. I would humbly suggest that cold molding techniques (using veneer as thin as possible) might overcome the problems you have seen. While not strictly analogous, the stresses within (at least parts of) a cold molded boat hull at high speeds over time probably resemble those within a fin. On the other hand, while this can retain the cosmetics, there goes the buoyancy aspect. I think that gets filed under “no free lunch” :->
-Samiam
[=Blue]Aloha Samiam
I am aware of the buoyancy arguments and have tried innumerable combinations of materials and construction methods to test it out. Of course we all know that end volumes and weights are more important than the actual materials used and as such the lightest material possible that is strong enough for the task, would be better if buoyancy is really the goal. Most woods are easy to shape but are really not that light and as such will have a marginal effect on buoyancy. Especially in that most fins are pretty thin these days compared to 30+ years ago. Of course, as in all things there are exceptions.
Additionally, what is common or popular is not always functionally best but as we all know, the superior economics of “popular” will usually override issues of superior function. Sometimes to the negative so much that progress is impeded. Other times the need for superior function is lost on a consumer base that is not interested as they are focused on other issues.
Well constructed wood fins shouldn’t be any problem functionally or structurally for 95% of the surfers and waves in the world. So wood fin advocates can rest easy.
Epoxies are probably better for mating wood and fiberglass in most applications. Mixing epoxy, wood and fiberglass might make it pretty difficult to achieve a particular flex characteristic compared to a simple fin of layered polyester and fiberglass though.
Thanks for the feedback.