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Old 04-14-2005, 11:27 AM
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Applying epoxy primer on bare metal?

I have been sanding a fender with 80 grit and then going back over with 180 on an orbital to get rid of the grinding swirls. I understand the Dupont epoxy sealer is designed to apply directly on the bare metal. I have some questions.

* Is 180 grit sanded surface of for adhesion? I understand this type of sealer has excellent adhesion.
* What do I clean the metal with? I know that I had some oil mist come out of my sander and onto the surface at one point and I am concerned. I know if I use a water based degreaser, it will rust. Would rust in the tiny scratches be a problem or is the sealer designed to encapsulate it?
* Can I safetly just wipe it down with lacquer thinner?

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Old 04-14-2005, 12:12 PM
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Sanding with 80 grit would be better IMO, offering more of a "tooth" for the epoxy primer to grab. I would clean the surface several times with a prep solvent designed for paint work, like PPG's DX330. I have not been too impressed with the current crop of epoxy primers nowadays. They appear to be mere shawdows of their former selves since complying with EPA regs. I think K36 primer/surfacer holds better on bare metal than epoxy primer.

Vince
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Old 04-14-2005, 01:47 PM
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Vince is right on on the metal prep procedure.
Buzz back over with 80 grit real fast to be safe.

Vince, RE: the K36 over bare metal any 2k primer and yes even the ones that say "direct to metal" you are always better off to use an epoxy.
2K primers just will not be there for the long haul.

Yes, you are right there has been a lot of downgrading with certain epoxies and VOC is a good excuse but most of the down grade has been cost cutting measures for the bottom line but even so the worse epoxy out there will do a better job over bare metal than the very best 2K primer.

Vince, we don't need you doing any of your street rods over down the road!
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Old 04-15-2005, 04:48 AM
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Quote:
Originally Posted by BarryK

Vince, we don't need you doing any of your street rods over down the road!
I here ya Barry. The problem I have with epoxy primer is this. I prepped my bare metal frame with 80 grit paper, wiped it clean several times with DX330. Sprayed with red PPG DP70 and top coated with DuPont Imron gloss black. While working to get the body in shape for painting I had placed masking tape on certain areas of the frame to prevent scratching it. While removing some of the masking tape the DP70 and the Imron pulled loose exposing bare metal . I know the proper steps were followed in the application. I also used the DP70 on my Rootlieb hood which I have not started on yet. Which leads me to suspect that the DP 70 on the hood might do the same thing after it is primed with K36 then painted with DBC . I know that the Imron that I used has been neutered to the point that it is not what it used to be either.
Vince
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Old 04-15-2005, 06:50 AM
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Vince-
I'm starting down the same path as you. Just a question or two for you, though.

After the DX330, did you wash it off with thinner? That stuff seems to leave a residue even after you wipe it down 3x. I followed the tech sheet, and was not impressed.

Do you think there was a chemical reaction due to 2 different brands of paint? This stuff is getting rediculous. You need to be a Nuclear Chemist to paint a car. Just staying within the PPG line, there are like products you can't use over one another.

Just as an example:

NCP270 over DP90LF with 402 Catalyst is OK, but not over 401 Catalyst

4,000 products, and no "road map" to tell you what to use thats SAFE with each other. The guys at the paint stores are ZERO help. They sell you the wrong stuf every day. You HAVE to read the tech sheets as they sell it to you just so you don't have to make trips back....grrrrrrrrrrr

Any PPG guys on here that can help me out?
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Old 04-15-2005, 07:00 AM
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Now I'm confused (which my wife says is my normal state of affairs). In the "Paint Bubbling" thread baddbob recommends sanding the filler skim coat with 180 and preferably 320 - and I respect his opinion. Here BarryK, who I also respect, says sand bare metal with 80 grit for better grip. So, are we talking about sanding the bare metal differently than the areas were skim coating/filling had to be done? Or do we have a difference of opinion, by two guys who know their stuff, as to which is best on the ENTIRE car - 80 grit vs 320? And I don't know if it makes any difference to the discussion, but I will be shooting an initial coat of epoxy primer over the entire car - some sections are bare, some have been straightened with filler/skim. I intend to shoot this thing today so hopefully I can get un-confused in the next couple hours.

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Old 04-15-2005, 07:16 AM
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vince.

back when i chenged over to epoxy from etching primer i had the same problems. what happened was i was too used to self etching which was alot more forgiving of surface prep and how clean the metal is. first thing that helped was i switched to a waterborne wax and grease remover. it works real good on bare metal before using epoxy. i noticed a hugh difference once i switched over to that. if you have to use regular solvent wax and grease then a final wash or 2 with acetone and a clean rag will work. it doesn't leave behind any residue. second, if i take a brand new white rag and wipe the metal down with it and get any discoloration at all on the rag then the metal is not clean enough, it needs to be perfectly clean. once i started doing those 2 things i never had an adhesion problem again.

as far as the sanding goes. you really need the good bite on metal so 80 grit is the way to go on that but 80 grit scratches on filler are going to be much deeper than on metal just because its softer so i usually do like badbob recommends and sand the filler area usually to 220 or so. the flatter you get the filler the less sanding scratches will show in the finish later if you happen to get any shrinkage.

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Old 04-15-2005, 07:17 AM
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cboy,
I have always used 80 on BARE METAL before epoxy.
You NEED a good scratch for bare.
Bob may be using the 180 on previous coats of epoxy before applying spot filler. I can't answer for him.
The 320 is WAY to fine for a good bare metal scratch for epoxy.
The 320 is normally the blocking over the final skim coat of filler BEFORE applying your 2K primer or your sealer coat of epoxy. Just makes less work and primer to fill the scratch.

I know it's confusing as everyone seem's to have a different "procedure" for things as some just use 180.220,320 for the blocking on spots.
It comes down to finish of the spoting putty. I believe the smoother you block the less material you have to spray to level it out.

Hope this helps some. Mike.

Found this in another thread.
Quote:
Yeah, All of my final sanding is done by hand. Air sanders are for rough in work or just fast material removal IMO. Taking your filler work from 180 grit scratches to 320 is only a few minutes of work, you can also apply a guide coat to make sure nothing is missed. Bob

Last edited by Bee4Me; 04-15-2005 at 07:26 AM.
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Old 04-15-2005, 07:30 AM
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Quote:
Originally Posted by Bee4Me
cboy,
I have always used 80 on BARE METAL before epoxy.
You NEED a good scratch for bare.
Bob may be using the 180 on previous coats of epoxy before applying spot filler.
Sounds to me like you DO sand with two different techniques. 80 grit for the bare metal and 180 (or smoother) for areas that are not bare (filler, prior paint, or prior primer). Does that sound about right? That is actually how I'm set up at the moment to paint today but figured I'd buzz down the filler with 80 grit if that was necessary to get a better bite (it's now finished with 180).
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Old 04-15-2005, 08:12 AM
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80 grit followed by 180 for bare metal is best IMO, 80 grit alone is good enough if you end up with enough scratches. Anything finer than 180 on bare metal is too fine IMO-I've seen epoxy adhesion failures on metal that was DA sanded with 320-just not enough texture there for the product to grab onto.

For me any bodyfiller or primers get finished with 320 before applying epoxy or urethane primer. 180 grit is fine before applying polyester primers IMO.

For most people 220 and 180 will work for the final grit on fillers and primers before applying primer but I just like using 320 to eliminate any chance of shrinkage showing sandscratches down the road---320 is probably overkill considering most people finish their filler work with 180 with no problems, but for the few minutes it takes to knock it down from 180 to 320 the extra assurance of no problems is well worth the minimal amount of time spent.

Everybody does things differently, I get a little anal about things on the high end jobs.
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Old 04-15-2005, 11:59 AM
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baddbob,

Actually I don't think there is that much difference of opinion after all. Sounds like it's more a matter of what you are prepping - bare metal or "not bare metal" (as in something with filler, primer, or prior paint already applied).

I'm ending up taking a little bit of everybody's advice (that way I can yell at almost every one of you when I screw it up). I did all the skim/filler areas with 180 and all the bare metal this morning with 80. I've stll got to do all my wipe downs (acetone) and clean up but hopefully I'll get at least the epoxy shot this afternoon (we got a beautiful dry day with high 60's so I'd really like to get it done).

Dewey
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Old 04-15-2005, 12:19 PM
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Quote:
Originally Posted by cboy
baddbob,

Actually I don't think there is that much difference of opinion after all. Sounds like it's more a matter of what you are prepping - bare metal or "not bare metal" (as in something with filler, primer, or prior paint already applied).

I'm ending up taking a little bit of everybody's advice (that way I can yell at almost every one of you when I screw it up). I did all the skim/filler areas with 180 and all the bare metal this morning with 80. I've stll got to do all my wipe downs (acetone) and clean up but hopefully I'll get at least the epoxy shot this afternoon (we got a beautiful dry day with high 60's so I'd really like to get it done).

Dewey
You'll be fine, just don't expect that epoxy to keep drying when the temp falls below 60. It takes a week for most epoxies to fully cure in good temps. Bob
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Old 04-15-2005, 12:57 PM
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Quote:
Originally Posted by cboy
baddbob,

Actually I don't think there is that much difference of opinion after all. Sounds like it's more a matter of what you are prepping - bare metal or "not bare metal" (as in something with filler, primer, or prior paint already applied).

I'm ending up taking a little bit of everybody's advice (that way I can yell at almost every one of you when I screw it up). I did all the skim/filler areas with 180 and all the bare metal this morning with 80. I've stll got to do all my wipe downs (acetone) and clean up but hopefully I'll get at least the epoxy shot this afternoon (we got a beautiful dry day with high 60's so I'd really like to get it done).

Dewey
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Really there is no difference in procedure, I think I was referring to bare metal BBob was talking about glazing putty. Where he just listed his procedure I pretty much follow the same thing.
Barry
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Old 04-15-2005, 05:26 PM
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Is there any drawback to applying 2 or more coats of the epoxy primer? a) I have enough paint left to do it and b) by gun played some tricks with me early on and I got some bad runs on one door that I'll need to sand out and re-shoot anyway, so just figured I'd go ahead and keep shooting til I use up the paint. The reason I ask is that the directions say to apply one wet coat etc. etc. , wait an hour (or two) before top coat etc. etc. but there is nothing about multiple coats of the primer itself. I'll also be shooting sandable primer over the top to do my final straightening anyhow.
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Old 04-15-2005, 05:44 PM
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as far as i know most epoxy is not designed to be built up thick. most epoxy does not require more than one or two coats. i would block out the runs and reshoot that area and stop there. barry might have a little more insight into why.
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