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Old 01-18-2014, 10:01 AM
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What did I do wrong

I sandblasted and painted some bumper brakets with Spi epoxy a year ago. Then set them outside on top of a retaining wall for the last year to see how they would hold up. They have been there rain,snow, hail, hot sun, what ever Mn weather could give them. They looked to be sand blasted good and to the bottom of the pits and clean. I put on two coats of spi.epoxy. Now they have rust coming back through in spots like where the bumpers where bolted to them before removed. What do I need to do resand blast, epoxy and try paint this time. If they dont hold up with out the bumpers on they will sure never make it all bolted back together.
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Old 01-18-2014, 10:30 AM
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It is hard to tell for sure but my guess is lack of film thickness. Even with 2 coats there must be enough film thickness to prevent oxygen from reaching the metal.

The paint appears to be bonding. I see no sign of peeling or loss of adhesion. I suspect that either rust was left on the bottom of the pits or the film build was insufficient to seal the metal from the oxygen source that allowed it to rust.

Barry K would be glad to discuss this with you.

John
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Old 01-18-2014, 10:40 AM
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One thing that I would be thinking about is how the primer was applied. If you applied two coats without a whole lot of time in between the second coat can re-wet the first and it moves a bit.

I say this because painting or priming items like that bracket the product flows away from the sharp edges. So you can put a coat on but really you have much less at the edges then out in the middle, MUCH less. Paint something like that a contrasting color to the primer and you will see even after a number of coats a distinctly thin color on those edges.

So if multiple coats allowing thorough flashing you still aren't getting the film thickness as you think and as you are out in the middle of the item.

So it's very likely those sharp edges around the holes and along the edges of the bracket weren't protected as you thought they were.

Brian
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Old 01-18-2014, 12:07 PM
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I guess I should of made this more clear. I gave it what you would normaly do then the next morning scuffed it with a red scuff pad and shot them again. I shouldn't have said two coats more like painted twice. These are for my own personal car a 1964 hawk Gt that I was in the middle of restoring but my wife ended up with cancer and things got put on hold so I thought it would be a good test as to how well they would hold up.
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Old 01-18-2014, 12:59 PM
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shot first of june and left outside. my guess would be some rust still present .
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Old 01-18-2014, 02:44 PM
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I went after it with some 120 on a da today. Looks like maybe a few of the pits may have had some rust left in them and I'am not sure my film thickness was as heavy as I thought it was. Took a grinder to the areas where the pits where and just ground it untill they where gone and had good clean metal. Sanded the rest good with the 120 and will reepoxy and I think this time I'll give it a coat of single stage paint.
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Old 01-18-2014, 05:17 PM
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Quote:
Originally Posted by swvalcon View Post
I sandblasted and painted some bumper brakets with Spi epoxy a year ago. Then set them outside on top of a retaining wall for the last year to see how they would hold up. They have been there rain,snow, hail, hot sun, what ever Mn weather could give them. They looked to be sand blasted good and to the bottom of the pits and clean. I put on two coats of spi.epoxy. Now they have rust coming back through in spots like where the bumpers where bolted to them before removed. What do I need to do resand blast, epoxy and try paint this time. If they dont hold up with out the bumpers on they will sure never make it all bolted back together.
What you did is perfectly normal, and the results that you got are about average. I Have heard the story many times. Epoxy primer It's not an airtight seal, contrary to popular belief. The use of a metal prep would have helped after blasting. Blasted steel that's been treated with metal prep can be stored indoors for a year without re rusting,That should tell you something. If you had used the topcoat that also would've helped. Epoxy on its own outdoors is subject to uv degradation. If this was an industrial environment a moisture cured base primer would be applied then the epoxy and then the topcoat.Re-blast it, metal prep then topcoat You should be good to go.
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Old 01-20-2014, 05:51 AM
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Originally Posted by shine View Post
shot first of june and left outside. my guess would be some rust still present .
EXACTLY.....wouldn't have happened if you used Ospho....no matter how clean and rust free you think it is theres still microscopic traces just waiting to grow into adulthood...simply encapsulating it in epoxy is not enough ...I've tried to explain this many times even showed it with pictures ....Ospho is the real cure for rust NOT epoxy...Epoxy is a great sealer from outside elements getting in but you need something that stops the small traces from growing...That's why I use Ospho and epoxy together ....I have stuff sitting outside for over 10 years without a trace of rerusting...this would be a great ospho test for you to try it on ,now that you've done the sandblasting and epoxy and its failed, just like I always said it would ,now try it my way and see what happens...
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Old 01-20-2014, 06:15 AM
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Oh boy. I know you guys never listen to me, but all go through it because I'm bored. Those brackets are really pitted so here's what I would do I would blast them, metal prep them or ospho them. I would then apply my primer to level up the pitting then I could apply the epoxy . Then the top coat. Mike, why don't you send him the can primer I gave you to do his brackets with?
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Old 01-20-2014, 11:24 AM
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Mike I saw a post where you can get it from Home Depot. I may check and see if I can find some and give it a try. These braces are off the rear bumper and I haven't gotten to the front yet but I'am sure they look about the same.
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Old 01-20-2014, 11:54 AM
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ace hardware carries naval jelly , oshpho and some other brands. tractor supply has milkstone .
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Old 01-21-2014, 12:57 PM
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Hp5311

Not sure if this is helpful to anyone in the thread. 8 years ago I have used a primer made by Tamco called 5311. It's a Direct to rust direct to metal primer in black. They explained that it has a product in the formula called Halox 630. The 630 is the active ingredient that converts and kills the rust all in one. I used it on a personal project I did around 8 years ago. I personally sandblasted the body, as I didn't want to take a chance, but I did a panel to keep in the elements for my own personal peace of mind. That panel was completely surface rusted, (happens quick here) and I spayed it and left it by my garage outside. It has not yet rusted through. I havent tried any other items they make, but this shocked me. So thought I would pass that info along if it helps.
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Old 01-21-2014, 02:58 PM
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Halox makes some really neat additives . I just checked out the tamco product data sheets. It looks like they have a nice selection of refinishing paints. Thanks for the info.
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