Bondo+rain=rust? Do you have epoxy under it?

 

that would be.... no

 

Well,
I've waited a few hours for one of the "Experts" here to answer this, but I think everyone will agree (maybe? ). From what I have learned, Polyester Bondo has Talc in it, so it has more than likely absorbed the moisture putting Water against bare metal (see where oldred said bond+rain=rust)? You probably now have rust forming UNDER the Bondo, so, in my opinion you will need to start over-

This time, especially in your part of the world, it would make some sense to get it back to bare metal and them Epoxy Prime first, then Bondo-anybody here going to throw me under the Bus?

 

Absolutely agree. Bondo + water = rust

Strip the bondo off the car spray epoxy primer on the bare metal (after you sand it to remove any rust), then you can put bondo back on. If you leave it like it is chances are that in time the repaired sections will rust from the inside out.

 

Yep! That pretty much says it....grind her out go too bare metal and start over. If you don't you will be sorry later on.

 

now that you've all bummed me out... 2 questions:
1-is there a epoxy primer that comes in a spray can? like maybe industrial red oxide?

and
2: if i have bondo under said red oxide, has that absorbed water as well? i have seen water bead up on some of this red oxide stuff. trouble is, i don't know what this stuff i used (elsewhere on the truck unfortunately), is made of.

it has only had water on it for a few hours, you sure i can't evaporate it outta there?

 

Well, the all metal fillers (under your bondo) don't absorb water to the extent that regular bodyfiller will, but believe they still do absorb some. Plastic filler absorbs it like a sponge, but keeping some heat on it should eventually evaporate the water from the plastic filler. If that red oxide primer you are talking about was a spray bomb product it is likely lacquer primer, and really isn't protecting anything. If you fillers have soaked up water and it reached the metal, there would be know way of knowing without grinding it out of there . Do you want to take the risk? If this is a cheapy industrial paint, just get some color on the thing paint job, I'd say leave it. If you will be forking out some cash for a quality paint, Grind it out, start over with a good epoxy primer base. The little amount bodyfiller costs compared to quality paint, or even primers isn't really worth taking any risk. It will cost you time, but better then the time and money to do it over later when bondo is bubbling up and rust pushing through. I believe they may make some epoxy which is 1 part, at least i've seen stuff called epoxy in spray cans. I doubt it would be anywhere near as good as the 2k stuff. If you don't have spray equiptment, many epoxy manufacturers say you can apply with a brush or roller, if yo allow the right amount of flash time.

 

Believe it or not there is a 2K rattle can available! I have not tried it as I have no need for it but I thought it interesting anyway, I don't know if they have an epoxy but they do have a 2K fill primer. There is some sort of mixing device on the bottom of the can and once activated it has a shelf life of, I think, about 12 hours.



www.autobodysource.com/pdf/july_aug2006/spraymax.pdf

 

thanks. as you might know or have guessed my whole truck has been in primer for the last four years. etching, red oxide, then etching again. i guess every bit of bondo on my truck, which isnt a ton, should be trying to leap off of it by now. i havent seen any signs of it though. i have had some surface type rust over broad areas start coming thru, which i sanded all off and repainted. again with red oxide then the green etching primer, just for color. i really need to get some real paint on this thing, and as it's a 4 wheeler, it wont be a spending paint job. i will prolly end up painting it myself or have a friend do it, so i wont feel bad about brushes scratching it all up. guess i ought to get with it soon. sb

 

water resistant bondo

My brother does a lot of his own body work.. age 73 He says he uses marine grade filler so he can leave it outside and not wory about moisture he says it costs about 5 times a much ar the cheap stuff

 

Probably is epoxy filler. This is used a lot on the marine industry, and is pricey. The stuff we use to use came in two different gallon cans which both parts were mixed equally. Notice how many people have asked if he used epoxy primer or recommended it for the repair.

 

that would be what i need... or a garage. the camaro goes to a consignment lot on sunday after Goodguys. so my garage will be ready. i used almost a whole $25 quart of All-Metal filler just to do a tiny tiny bit. i kept putting in on with not enough catalyst cause it doesnt change color and having to scrape it off and start over. i just finally got it right when it rained. i have left a halide light under it and it was kinda hot to the touch. i have plastic wrap over it and i havent seen any condensation on the inside of it. there is tape on the top of it. so i am wondering how there could be much water in there if i dont see condensation from water evaporating on the underside of the plastic wrap. either the wind blew the hot vapors away, but i dont see how as i have the sides taped down too, or i didnt get that much absorbsion. either way. it's very hot. i dont see how any water could stay in there at that temp.

 

new Bondo and rain

It just happened to me, luckily I had about four hours of cure before it started a light rain, I went out and duct-taped a garbage bag over it as good as I could seal it (the hole is at the corner of the rear rocker panel and wheel well, and there's a support jack in the way, of course). I also rubbed some baking soda onto the surface of the Bondo and dumped a small box of baking soda into the garbage bag as a mild desiccant. The baking soda will create a dry area that should pull moisture out of the air and hopefully out of the Bondo as well. Tomorrow is expected to be sunny, I will test it at the end of the day after it's had time to dry by chipping a tiny amount of Bondo off and checking the bare metal for rust. I will put a fresh bag/baking soda over it throughout the day, hopefully with a better seal when I can see it in the light and remove the jack. I have never heard of this method of protecting Bondo from rain from anyone else, I invented it. I hope it works.

 

yep

yep... Fill the holes with metal - put the epoxy primer on first, then bondo then and a sander-sealer on before paint. i painted a car in 93 that's never been parked indoors. -42C winter / +35C summer for years and the bondo still is in the front fender where i put it. nuff said.

 

Well, the all metal fillers (under your bondo) don't absorb water to the extent that regular bodyfiller will, but believe they still do absorb some. Plastic filler absorbs it like a sponge, but keeping some heat on it should eventually evaporate the water from the plastic filler. If that red oxide primer you are talking about was a spray bomb product it is likely lacquer primer, and really isn't protecting anything. If you fillers have soaked up water and it reached the metal, there would be know way of knowing without grinding it out of there . Do you want to take the risk? If this is a cheapy industrial paint, just get some color on the thing paint job, I'd say leave it. If you will be forking out some cash for a quality paint, Grind it out, start over with a good epoxy primer base. The little amount bodyfiller costs compared to quality paint, or even primers isn't really worth taking any risk. It will cost you time, but better then the time and money to do it over later when bondo is bubbling up and rust pushing through. I believe they may make some epoxy which is 1 part, at least i've seen stuff called epoxy in spray cans. I doubt it would be anywhere near as good as the 2k stuff. If you don't have spray equiptment, many epoxy manufacturers say you can apply with a brush or roller, if yo allow the right amount of flash time.

USC All Metal is 15% - 25% talc, so how can it be all metal?, because it bonds to all metals. What a marketing gimmick.

 

Well,
I've waited a few hours for one of the "Experts" here to answer this, but I think everyone will agree (maybe? ). From what I have learned, Polyester Bondo has Talc in it, so it has more than likely absorbed the moisture putting Water against bare metal (see where oldred said bond+rain=rust)? You probably now have rust forming UNDER the Bondo, so, in my opinion you will need to start over-

This time, especially in your part of the world, it would make some sense to get it back to bare metal and them Epoxy Prime first, then Bondo-anybody here going to throw me under the Bus?

Not me,your right on...another good reason for epoxy first...

 

all metal is another one of the marketing wonders of the 60's. worst stuff i have ever used. it expands and shrinks for ever. i would remove all of it and start over using better products.

 

I just had a car friend over a few day's ago, And we was talking about this very thing... My friend looked at me and said...It can't absorbed the moisture,, It's a plastic filler.. :drunk: :drunk: :drunk: :drunk:

I said YEA !!! OK !!!!! :mwink:

That's why I'm a strong believer to put epoxy primer first.. Then Filler..

 

that would be what i need... or a garage. the camaro goes to a consignment lot on sunday after Goodguys. so my garage will be ready. i used almost a whole $25 quart of All-Metal filler just to do a tiny tiny bit. i kept putting in on with not enough catalyst cause it doesnt change color and having to scrape it off and start over. i just finally got it right when it rained. i have left a halide light under it and it was kinda hot to the touch. i have plastic wrap over it and i havent seen any condensation on the inside of it. there is tape on the top of it. so i am wondering how there could be much water in there if i dont see condensation from water evaporating on the underside of the plastic wrap. either the wind blew the hot vapors away, but i dont see how as i have the sides taped down too, or i didnt get that much absorbsion. either way. it's very hot. i dont see how any water could stay in there at that temp.

This thread isn't going to do you much good if you plug your ears to all the advice offered and keep trying to talk yourself out of doing the correct repair. Skip a step now means 100 additional steps you have to take in the future. I personally would have had it tarped up if I had it in the elements with exposed filler or a primer that's anything less than an epoxy.

 

Filler...........

Bondo (or other brand names) are HYGROSCOPIC,that big word means that they absorb water,remove all filler,back to bare metal,epoxy prime,with 2 good coats,then filler on top of the epoxy primer,after you sand your filler,re-apply 2 more coats of epoxy,to seal the filler,then you will be good to go...you MUST seal the filler,BEFORE painting.or the filler will soak up the paint leaving you with a dry area. :nono: :nono:

 

Alright, it failed miserably, the condensation found its way in and collected on the inside of the bag and stayed there long after the outside humidity became dryer. Also the baking soda held the moisture like a sponge. There may not be a good solution for this situation. Check the weather report for the next couple of days before applying Bondo to an outdoor car. I don't think I experienced much of a problem, eventually it dried and although my primer and paint did not adhere well, I had to scrape a lot of it off, the Bondo itself remained strong and so I re-primed and repainted.

 

Holy Back from the Dead, Batman!

Well, since i started this thread, my truck has changed paint, (its all urethane epoxy primered), but i still HAD that the same issue, about three months ago, mainly because when i shaved the hood emblem, i had the body shop seal the holes and they welded little inch squares over them on the inside of the hood. well to my dismay, they didn't seal the holes, they did a slitty job. moisture got in there over the years and cracked the bondo up, rust from the inside out. i never did scrape it all off. i finally had to a couple of months ago, naturally, when i put the truck up for sale, i start to fix stuff i shoulda fixed years ago. so i did take it all down to metal, but i did not go back and read this thread first!!!so i didn't epoxy the metal FIRST, but i DID epoxy after. i also took undercoating spray and sprayed over those squares sealing any holes up. so anyway, so far so good, wish i would have done what was on here, but i forgot i wrote this post. i didn't slather it on so thick this time either, and btw, in the first post when i said two and four inches, i'm glad nobody thought i meant THICK! i did mean sideways. oh well, i am happy thinking the undercoating will stop water and that i did go down to bare metal. Should i be?

 

boatbob2 hit it right. Most body fillers are polyester resin, and polyester resins absorb water out of the air even if it does not rain, or even if the humidity is low. Water on bare steel means rust, even if covered with body filler.
Do it right one time, or redo it later. The choice is yours.