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Author Topic:   Marine Epoxy: Comparison of WEST Systems to BONDO
FiveFeezy posted 08-11-2007 11:24 PM ET (US)   Profile for FiveFeezy   Send Email to FiveFeezy  
I have been repairing the rail on my 13 footer using, "The Whaler Way," described on this site. After I got the shape pretty close with the fiberglass and resin, I swithced to using the West System 407 fairing filler to get a smooth finish.

However, I have cut a few corners using the 407 and now I am concerned. First, instead of buying the expensive West Systems epoxy resin, I have used the cheaper Bondo fiberglass resin to mix with the 407. But my main concern is that I didn't wet my new fiberglass repair down with pure resin/hardener before I applied the resin/407 mixture. I didn't know that I was supposed to do that until I already had the 407 mix applied.

So I am wondering if the 407 mix will stick to fully cured fiberglass or should I sand back down to the fiberglass and start all over?

Thanks to all for the help.

jimh posted 08-12-2007 06:04 PM ET (US)     Profile for jimh  Send Email to jimh     
Custom boat builders build million-dollar yachts with WEST System epoxy, but I do not recall ever hearing that any custom yachts have been built with BONDO. This may be information from which you can make an inference about the relative quality and strength of the two epoxy formulations.
Tarpun posted 08-12-2007 09:08 PM ET (US)     Profile for Tarpun  Send Email to Tarpun     
Is the bondo resin epoxy or polyester? If polyester it will have poor bonding with the old glass/resin. Epoxy resin is much stronger.
PeteB88 posted 08-13-2007 09:54 AM ET (US)     Profile for PeteB88  Send Email to PeteB88     
You are kidding right?

Keep doing your research but in my experience cutting corners and stepping over a dollar to pick up a penny as regards boat finishing ALWAYS impacts the final results adversely especially finish quality, durability and years . What you did might work but it makes no sense. I can only comment on polyester resin/bondo over wood boat hulls as opposed to epoxy resin/glass cloth over wooden hulls. In most cases epoxy is superior in every way. The only thing you have to worry about is proper coats of marine paint or marine spar varnish (if bright finish is desired) over epoxy to protect against UV degradation.

Maybe this is a bad example but my neighbor, who has a masters in historic preservation architecture, decided to strip off most of the paint on his doug fir clapboard sided house that is about 75 years old. As he got into the project, besides the hours and hours and hours of work, he decided to cut costs by using an inferior (and not recommended) exterior putty to fill cracks and nail holes. I suggested he get a gallon kit of West Systems and use that with filler for the big stuff and high quality commercial grade spackle or exterior stuff for the small or nail holes. Instead he proceeded.

Within three or four months EVERY spot on that house, all four exterior walls where he used the cheap stuff POPPED out or bubbled up. He had to go over all of it and fix and repaint.

Good luck! I hope I am wrong in your case.


Binkie posted 08-13-2007 11:16 AM ET (US)     Profile for Binkie  Send Email to Binkie     
As you know wood expands and contracts, unlike fiberglass, and any filler that will dry hard like epoxy or polyester resin will fail with the movement of wood. That's why fillers for construction use need to remain pliable. I would venture to say West Systems epoxy would fail also if used in that manner. there are different grades of polyester fillers, available at commercial automotive paint stores. Bondo seems to be a common name, and it is a cheap grade sold at auto parts stores. If you`ve ever had body work done on your car, I`m sure it was covered with a THIN layer polyester filler. I`ve used it for years as a fairing compound on glass boats with never a failure. Marine Tex is the same product, only sets up slower to reduce waste. Polyester fillers,(Bondo) is not for structural repairs, of course, its just a surfacer, use epoxy and fiberglass mat or cloth for structural repairs.


FiveFeezy posted 08-13-2007 01:12 PM ET (US)     Profile for FiveFeezy  Send Email to FiveFeezy     
Just to clarify, I'm not using Bondo body filler that is used to fix dents on cars. I am using the Bondo brand fiberglass resin mixed with fiberglass mat or with West Systems fillers.

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