Fairing/Filler from 3M

I called Bondo (a 3M company) about their email reply to questions about using Bondo as fairing on boats. The conversation was quite amazing....

Spoke with Thomas B (3M Bondo Technical Service) about my Hard Top project and how he said in his email that Bondo will adhere to the epoxy as long as the epoxy was sanded with 80 grit. He stated that Bondo filler is a mechanical adhesion, not a chemical bond. Thats how it sticks to bare steel, fiberglass, etc.

What was interesting is he has personally visited the Maxxum, Stingray, Bahah(sp?) and other boat assembly plants where they use BONDO as fairing compound on the boats!!! These plants buy Bondo filler to fix imperfections and general fairing during the manufacturing process.

When I brought up that the boats were made from polyester resin, not epoxy, he agreed and said that for EPOXY fairing, to use the premium body filler sold under the name MARSON PLATINUM that has additional adhesion specifically designed to stick to difficult surfaces like epoxy, galvanized steel, and other slick surfaces.

Marson Platinum is not sold at auto parts stores. It is available at Auto Body Supply shops and online.

I was pleasantly surprised at this mans knowledge of the boat industry, his first hand experiences with major boat manufacturers using filler, and how he candidly and openly spoke about the products and the problems with epoxy.

For those of us who have made our own epoxy fairing compound my mixing glass bubbles and silica fiber in epoxy, you know how hard it is to sand and shape when cured. I think the Marson filler is worth a try.

Just thought I'd share that.

Re: Fairing/Filler from 3M

I just did some glassing and used Bondo product by 3m are you talking about regular bondo car filler? they do have poly-filler there is long hair, short hair, and glazing putty.

Re: Fairing/Filler from 3M

Interesting, I've been to those plants and worked in the production areas and even done patch and repair classes for the detail departments, I don't recall ever seeing any of their products being used or even in the shop.

Builders will at times use that type of product when mocking up a new design, so I don't doubt they do sell some product to them, but when doing repairs on boats they typically use marine grade products.

Re: Fairing/Filler from 3M

coastalcruiser said:

I just did some glassing and used Bondo product by 3m are you talking about regular bondo car filler? they do have poly-filler there is long hair, short hair, and glazing putty.

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No, it not regular Bondo. Its a premium body filler with additional adhesion properties to stick where traditional bondo does not.

Re: Fairing/Filler from 3M

i am doing some farring right now....i didnt want to spend the money on a 5 gallon of poly fair......so im using a short strand filler for the thick farring.
but im going with glass bubbles, and talc. (the talc cannot be used below thw water line as it is absorbant)
its sanding qualitys are good.

as far as epoxy mark....im not sure. but as ondarvr said i think the only place for bondo in production building might be on the plug for farring, but not on the actual boat.

Re: Fairing/Filler from 3M

oops! said:

i am doing some farring right now....
but im going with glass bubbles, and talc. (the talc cannot be used below thw water line as it is absorbant)

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I was reading on a boat building website that once the talc is mixed in resin, that it doesn't absorb water, same as mixing in wood flour or wheat flour. Of course, thats one builders opinion.

So now you're making your own Bondo? (poly resin + talc)!

BTW, I spoke to a major auto body supplier in my area today looking for the Marson Platinum. They said they don't carry it, but could have it in a day or so. He also said it is one of the best body fillers on the market. His opinion as to why some bodyshops work lasts longer than others has a lot to do with the products they buy. His opinion is you get what you pay for in body filler. He also said the high end filler by Evercoat is a good one too.

Re: Fairing/Filler from 3M

ooops!,

i didn't want to spend the money on a 5 gallon of poly fair

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they have it in liter size at crappy tire, I went to lordco not much selection and real expensive.

Re: Fairing/Filler from 3M

Talc is one of the main reasons body filler doesn't work well around water, even when mixed thoroughly with resin it will still absorb water and fail. The resin used won't hold up under water very well either, so you get it from both sides. As you upgrade the resin and fillers the water resistance improves, but the price goes up too.

Re: Fairing/Filler from 3M

ondarvr said:

Talc is one of the main reasons body filler doesn't work well around water, even when mixed thoroughly with resin it will still absorb water and fail. The resin used won't hold up under water very well either, so you get it from both sides. As you upgrade the resin and fillers the water resistance improves, but the price goes up too.

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I have to agree that I have seen unprotected body filler fail in boats. But I can't explain why it lasts for 10 years in a car sitting outside in the rain, snow, baking summer heat, rattled by slamming doors, jarring pot holes and all around vibration, and perform flawlessly when all that protects it from the elements is a 0.010" thick coat of primer and paint. The metal and body filler expand and contract at different rates. All that holds them together is a mechanical bond. Yet in even more extreme conditions than a boat operates in (-20 to over 100*), the body filler performs flawlessly on a steel car, and even fiberglass Corvettes too.

I guess I'll find out first hand what the problems are using body filler above the water line.

Re: Fairing/Filler from 3M

If you do a little history research on "bondo" you will find that it origin or creation was developed at the request of wooden boat manufacturers for filling the screw holes in the sides of the boats where they attached the lapstrakes or planking to the ribs of the boat on boats that were to be painted.

Re: Fairing/Filler from 3M

That's interesting.

I don't find epoxy that hard to work with and I've fixed some pretty ugly stuff with it. What worked for me was removing the bulk of the material before the resin fully cured. Hate to keep harping on the surform tool but it was a lifesaver for me.

Re: Fairing/Filler from 3M

I've found if you really want a good looking part it almost always has to be molded from a properly prepared plug and mold,

fairing and sanding a material which is tough enough for the finished product is a tough slog to shape when cured.

So it has to be near perfect when it kicks, inside curves especially to get the finished look without spending hrs working at it.

having to fair slight imperfections just goes to show the work that goes into a good plug for a good mold.

I never found anything that makes epoxy easy to sand, grind maybe.

Getting an outside curve can be just as difficult without using template knives, I find it a whole lot simpler to just use something pre-shaped like mooden molding and glass over that.
For complex and compound curves , just do yer best and try to accept imperfection.

Re: Fairing/Filler from 3M

West system has a filler that is called 410 that is added to the epoxy resin after the hardner has been added and mixed that is very easy to sand and shape. Poly-fair is another polyester product that is easy to sand and shape as well. However i agree with the shape it while its still green theory, saves alot of sanding if you didnt get it close in the application stage.