hnesitd1

I've read a lot of references to BONDO. Is this the standard product that is available in automotive repair stores? It seems to be very popular for finishing fiberglass fabrications. Can BONDO be used indoors? Please advise with specific product information. Thanks guys.

davidfee

Bondo is a polyester resin-based material. It is available by this (and other names) in most home and automotive centers. It is basically polyester resin filled with milled fiberglass (and maybe some other stuff) to make a very thick paste. You work in some creme (MEKP) catalyst and apply it ... usually with a plastic spreader.

Because it is polyester, it stinks like you wouldn't believe and should not be used without good ventilation. I use it only for tooling... not on my airplanes.

-David

newbiepilot

Hi,
Why don't use it on your airplanes? What do you mean by tooling?
Also, I was just wondering if you can use bondo as a filler for sharp corners and if it has any strength or take any weight.
Can bondo be used like fiberglass would be used in a layup because it has milled fiberglass in it.
Thanks so much for the info.

davidfee

Bondo is heavy compared to epoxy with microballoons. If you are using polyester resin to make your airplane, then Bondo might be ok as a filler, but it will still be very heavy and hard to sand. If you have sharp corners in a mold then what you do is mix microballoons and/or some other filler into your epoxy. If you want to sand it later or if weight is important, then use microballoons. If it needs to be strong, then use colloidal silica, milled glass or chopped carbon strands.

-David

davidfee

Tooling is a term which refers to things you make to help you make the actual part you want to make. A mold is tooling. A fixture is tooling. I use Bondo to fill the gap between a plug and the parting board when I'm making a mold. Sometimes I use Bondo to make a plug because it sets up quickly. But it is heavy and has very little strength on its own.

-David

hnesitd1

Thanks for the candid info - very helpful

Mike James

Just for clarity...

"Bondo" is a brand name, including several different polyester-based products. It is not a single product.

You can buy polyester resin,(with no filler) or the filled paste mentioned above, and other products, under the "Bondo" name.

davidfee

Very good point, Mike. I should have specified that.

-David

Kevin Greene

My Feedback: (85)

Also, regular "Bondo" doesn't have any glass fibers in it. It is straight fillers and resin. There is a type of Bondo that does have glass fibers imbedded in it but it is unsuitable for finish work as the fibers are exposed when sanded, leaving the surface fuzzy and full of pin holes. The Bondo with fiberglass is used in the automotive industry to bond, for example, a hood scoop to a hood. The fibers prevent cracking. You must topcoat with regular Bondo.

"Bondo" is also not really recommended as the final finish before priming due to the possibility of pin holes and not being able to get a fine feather edge. There is another product for this.....It is a catalized spot putty. This catalized spot putty is extremely smooth and light...Ideal for final finishing before priming. The best things about catalized spot putty are light weight, excellent feather edge ability, no shrinkage and EXTREMELY easy to sand. Much easier to sand than any epoxy/microballoons mixture that I've run across.

Some guys like to apply a lot of primer to fill sanding scratches, pin holes, and provide a feather edge. This is a big mistake. Bondo and primers can shrink, even catalized primers. When this "shrinking back" occurs, all of the imperfections that were once covered up become noticeable. Catalized spot putty has very little shrinkage due to the thin application. It really is wonderfull stuff...Available at you favorite automotive paint and supply store.

Kevin

davidfee

Ok, so looking at my can of Bondo #262, the fillers are talc, magnesite and fibrous glass. Talc and magnesite (magnesium carbonate) are minerals and the fibrous glass was what I was referring to when I said "milled glass."

Anyway, Kevin is most certainly correct when he says that Bondo makes a great many products.

happy filling,
-David

Kevin Greene

My Feedback: (85)

My generic brand of Bondo (EverCoat) lists what yours says sans the fibrous glass.

Kevin

hnesitd1

All very good info guys - thanks for your time