how to glass on fins properly

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flsurf's picture
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how to glass on fins properly

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Can anyone advise me how to glass on fins properly so they don't get weak and give way at the base after time?  When I was younger I used to build and ride my own boards but always put in fin boxes. I recently began shaping and glassing my own boards again and have thoroughly enjoyed doing all the work myself. It has given me great satisfaction to ride a board I created and built from start to finish. I am also building my own fiberglass fins from scratch and mounting them...they are working really well, but the bases are giving way over time. Recently on a new board on the first take out, I lost a keel fin on a hard bottom turn...what's the secret...is it in how you wrap the glass rope? They all look really good when I'm done with the sanding and glossing, but I must be doing something wrong when I'm mounting them.

reverb's picture
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Re: [flsurf] how to glass on fins properly

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...hello,

move the post to general discussion.

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Re: [flsurf] how to glass on fins properly

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I presume you have searched for existing threads.? Since you have already put fins on before, it sounds like you know the drill but want more durability. Here's a quicke review of what you probably already have done.

Build or buy fins with sufficient thickness to handle stress of turning (1/4"+)

Marked blank or lam. coat or sanded hotcoat. (Better to do fin install on laminating coat vs sanded)

Tacked fin(s) on opting for resin, 5 min. epoxy, hot glue, 2 sided tape, etc. w/cant & toe in

Fin(s) to be glassed on are NOT shiny, sanded and ready for glassing on

Created a work table: I tape waxpaper on bottom of bd. to do lamming (wetout) of patches (3) that will go on each side of fin. Some glassers just perform this on the laminate.....this can get sloppy with loose strands & resin drips so I opt for the waxpaper.

Take 6-10 strands of glass rope (I use roving), flock it on a hard edge to break up rope softer to allow for easier wetting out. You can wet out the entire length of rope then trim to each side of fin (slightly longer approx 1/4" past leading/trailing edges of fin. Optional metod is to precut the rope as stated while dry and set next to each side of fin. If you precut, take a 1" chip brush and cut bristles half the length slightly rounded or approx. alf circle. You will use the brush to wet out each glass rope section then smoosh it against the base of the fin. Use the preshaped brush or your finger to push bubbles out of the rope fillet. Pinch the rope on each side of fin front and back so that when you put glass layers on, the rope from each side is trapped by cloth from each side. This will give you a good solid glass leader directly in front of the fin and also at the trailing edge.

You can lam cloth onto fins with a 3" brush cut short to make for stiffer bristles by prewetting the fin face than laying on cloth layers staggerng layers for easy fairing when sanding, but it is faster and easier to prestagger the layers wetting them out with a squeegee on the waxpaper. Then lift 3 at a time and place onto each side of the fin, work your bubbles out from the fillets and fin face as needed.

Trim extra cloth when resin has kicked and is like semi hard cheese. If you pinched the extra bit of rope together then layed up your layers, you should have no voids forward or aft of the fins where the glass layers meet from each side.

You can surform or knock down glass layer edges, drips, etc on bottom laminate once hardened previous to doing more resin work. If you gnarled on sloppy strands or whatnot, brush on a little styrene and apply a cheater aka sweet coat of lam around the bases of ech fin and allow to kick before applying the hotcoat aka sanding coat.

You say your problem is the fins cracking at the base or not lasting long and popping off. Perhaps you have been adding a lot of styrene to your fin layup resin to get really clear glass rope fillets? If so, back off on the styrene as adding a lot chages the molecular linkage of the original mix. If you tacked on your fins with 5 min. epoxy and you used more other than just on the base of the fins, you may compromise the bond of your fillets and support cloth.

If you want superior strength to what you are now getting, .try additional strips of cloth at the base area of your fins. Or use Warp glass running the majority of strands vertical up the fins. Warp glass has 2/3rd's of the strands running lengthwise aka 'on the warp' vs. regular cloth that 50% warp/50% fill. For a extreme reinforcing, purchase unidirectional cloth and put some running vertically up the base area of the fins along with your regular cloth. That will give you the greatest support possible against lateral pressure that fins experience.

P.S. Not spell checked, but i've done my part. Good luck, keep surfing.

flsurf's picture
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Re: [reverb] how to glass on fins properly

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this was my first post on swaylocks...how do I move it to general...cut and paste?

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Re: [deadshaper] how to glass on fins properly

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Thanks deadshaper for your kind response and detail! great advice and I really appreciate your reply...I will apply the techniques you suggest and let you know if I have further questions

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Re: [flsurf] how to glass on fins properly

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...to avoid any mistake better ask one of the moderators, like K Melville.

happens that most dont enter here and go directly to general disc

so there you ll have more opportunity of responses; but in this case DS answer is pretty good.

I can add that might be your problem is in the sanding stage.

if you sand too much with a harder pad in the fillet of the base, you finish sanding all the patches...

also the leash; a leash must be straight and never rolled around the board and tense

to avoid grabbing or whip the fins when fall out occurs and of course ballast (dead weight)

...transportation, yes, lot of fins start to crack in the base due to bad car transportation.

-a bit more steps to do and check if you need to put a fin in a used damaged old board

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Re: [deadshaper] how to glass on fins properly

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one trick that has worked for me is to do the fin layup backwards - put the cloth up next to the fin and put the fin roving on the outside.  also use extra patches at the base.  If you are careful - you dont get any bubbles and when you sand your fillet smooth, you are sanding into the fin rope instead of the cloth so all your strength remains!!!!!!!!!! (there is little strength in the fin rope - it is there just to get that nice fillet)


the really good guys can layup the fins so that you dont have to sand into the cloth to get things smooth and deadly but i am not that good!  i still see these fins crack at the base under the cloth (in the rope - esp. if the rope is too resin rich)

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Re: [flsurf] how to glass on fins properly

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.


 

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Re: [grasshopper] how to glass on fins properly

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"there is little strength in the fin rope"?

I'm not sure if I can agree with that. I might if we viewed it as linear lines running parallel with the fin and that the fin never experienced ANY torsional flex, but I don't think that is the case...particulalry with today's modern tri fins that are thinner than back in the 80's.

Doing the fin 'in reverse' might be workable but I wonder if you are getting an air pocket or promoting a hairline along the base of the fin due to the glass weave not fully filling in at the base of the fin? It obviously works, as you have had luck with doing it that way, but there is no way I opt for sanding glass rope when I can do graduated layers of 4 oz. in a clean layup and hotcoat and sand the hotcoat resin instead. In fact a clean laminated board and proper hotcoat entails sanding very little glass weave period.