Epoxy fillets ingridients confusion

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BarraMan
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Re: Epoxy fillets ingridients confusion

Post by BarraMan »

cape man wrote: Mon Mar 29, 2021 2:17 pm Not to add another answer to what was a simple question... but I prefer wood flour mixed with epoxy to the consistency of thick peanut butter for my filets. No sanding required if you apply the fiberglass within 24 hours of the filet. Wood flour and epoxy IS very strong, and perhaps the cheapest filler you can find (it is the cheapest sold here). For structural components like filets and overfilling holes that will then hold a screw, wood flour is really great stuff. It is harder to sand than some of the other fillers that are more suitable for fairing compounds.
I was starting to get up a head of steam and ready to fire off a lengthy post until I read this one. I agree with Capeman 100%!

95% of the fillets in my boat are a mix of epoxy/woodflour, and I am in no doubt that they provide significant structural strength as well as provide a smooth path and workable radius for glass tape.
The other 5% have some carbosil in the mix for vertical fillets that otherwise might sag.

Each to their own, but personally I can't imagine adding micro-balloons to structural fillets! :doh:



Dougster
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Re: Epoxy fillets ingridients confusion

Post by Dougster »

Four builds and I never used anything but wood flour for fillets. Didn't know any better and kept it simple. The fillets seem rock solid to me and wood flour cheap.

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OneWayTraffic
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Re: Epoxy fillets ingridients confusion

Post by OneWayTraffic »

BarraMan wrote: Tue Mar 30, 2021 5:44 am
Each to their own, but personally I can't imagine adding micro-balloons to structural fillets! :doh:
Neither did I originally but a well known Aussie designer uses a 50:50 mix of glue and fairing fillers with biaxial over it for his plywood glass composite boats. So I looked into it, and the Physics makes sense. If the fillet is just there to carry the glass around the curve then that's what matters. You could use wood, balsa, putty, or foam pads or almost anything. The glass carries the load and the fillet is mainly put into shear or compression if anything. A microballoon filled putty can be at least as strong compressively as the wood that it lies over.

A microballoon fillet without glass on the other hand would need to be much bigger to have equivalent strength. I wouldn't go there either.

OneWayTraffic
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Re: Epoxy fillets ingridients confusion

Post by OneWayTraffic »

Dougster wrote: Tue Mar 30, 2021 9:33 am Four builds and I never used anything but wood flour for fillets. Didn't know any better and kept it simple. The fillets seem rock solid to me and wood flour cheap.

Dougster
I'd like to have tried wood flour but it's not commercially available here in NZ. I'm not about to go looking at sawmills due to the unknown species, and prevalence of treated wood. So I stuck with WEST.

Dougster
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Re: Epoxy fillets ingridients confusion

Post by Dougster »

Yeah, I wouldn't have used an unknown either. West is safe.

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VT_Jeff
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Re: Epoxy fillets ingridients confusion

Post by VT_Jeff »

Dougster wrote: Tue Mar 30, 2021 9:33 am Four builds and I never used anything but wood flour for fillets. Didn't know any better and kept it simple. The fillets seem rock solid to me and wood flour cheap.

Dougster
I like wood flour fillets as well, thickened to peanutbutter. I like to put down some raw epoxy in the joint first and let it soak in a bit and get tacky so that I KNOW that I'm getting a good bond from the fillet to the wood. Otherwise I worry that the wood may suck the epoxy from the flour at the surface.

Once the fillet is pretty firm, I use a bare finger dipped in acetone to smooth it out.
There are only two seasons in Vermont: boating season, and boat-building season.

cracked_ribs
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Re: Epoxy fillets ingridients confusion

Post by cracked_ribs »

I'm also a straight wood flour guy. Whether the fillet is structural or not would depend on the design. On some designs that I've seen you really stand to benefit from a strong fillet, others not so much.

I also like to lay down some epoxy on the wood and let it soak in a little before laying the fillet on. I don't think I've ever seen a starved joint that I did, but it's something I worry about so I like to hit everything with unadulterated epoxy (and ideally a heat gun) first.

I'll occasionally add fumed silica if I think I need extra "hold" in a weird location. I'll also occasionally add a really small amount of talc, just because it tools so beautifully.
I designed my own boat. This is the build thread:

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