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Old 09-25-2008, 06:48 PM
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DuPont epoxy primer - beginner questions

I went to the local Dupont dealer today and asked what epoxy they sold. They gave me a tech sheet for DuPont 25xxS Epoxy DTM Primer-Sealer. Is this the right paint (and best product from DuPont) for bare metal? The people at the shop were pushing etch/urethane primer as the preferred method so I got a little worried and figured I should come home and ask here first before I bought the paint.

My plan is to strip to bare metal, remove rust as much as possible, spray the epoxy (2 coats), then filler over the epoxy. Then, touch up epoxy over the filler areas. Then prime the entire vehicle with high-build primer.

Assuming it's the right stuff to use, I have some specific questions about the tech sheet.

1. What does DTM mean?
2. What is chromate?
3. What does it mean when they call it a "non-sanding" primer?
4. I'm confused on the recoat window...can someone explain in simple terms. If I spray another coat over the filler, do I need to sand?
5. It says let dry for 16 hours minimum before applying filler...do you need to sand before applying the filler?
6. Question not specific to this primer...when someone says to "scuff," what exactly does that mean?

Thanks, Scot

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Old 09-25-2008, 07:12 PM
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DTM means, direct to metal.. the pro's can answer the other questions better than I can
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Old 09-25-2008, 07:28 PM
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Quote:
Originally Posted by ScotY

1. What does DTM mean?
DTM is Direct To Metal

2. What is chromate?
Zinc Chromate is a rust inhibiting primer. Used primarily on aircraft. It's a olive green to light green in color.

3. What does it mean when they call it a "non-sanding" primer?
Non-Sanding is just that, you don't sand it.

4. I'm confused on the recoat window...can someone explain in simple terms. If I spray another coat over the filler, do I need to sand?
"Recoat Window" is the amount of time that recoating must be done in. In other words, if the recoat window is 4 hours, you can recoat within that 4 hours. If you wait longer than 4 hours, you must SCUFF the surface before applying another coat of anything.

After you do your filling and block sanding, (to get the body work smooth and straight) you use the "Epoxy" as a sealer to seal any bare metal that may be showing through the body work. As you sand the body panel smooth and straight, you will get down to bare metal in places. If you don't, you are using too much filler to make repairs. You DON'T SAND the sealer (Epoxy).

5. It says let dry for 16 hours minimum before applying filler...do you need to sand before applying the filler?
You don't need to sand the Epoxy before applying the filler.

6. Question not specific to this primer...when someone says to "scuff," what exactly does that mean?
SCUFF mean to scratch, or make dull looking. Normally you will use 3M scuff pads, green, maroon, or grey. The "scuff" the surface to give paint something to bite into.

I hope that answered most of your questions.

One thing to remember, The guys at the paint supple store, their job is to SELL PAINT. I have found that they will sand you a lot of stuff you don't need. So be careful.

Frank
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Old 09-25-2008, 07:44 PM
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Thanks, that helps a LOT!

Re. the chromate...it says "DTM is available in lead/chromate free ValueShade and chromate for use under body filler, polyester putties, primer-surfacers and topcoats." Is it safe to assume both types (with and without chromate) can be used under filler? I'm guessing that's true.

For recoatability, it says "DTM may be recoated at any stage of cure. DTM can be topcoated within 24 hours air dry without sanding the DTM. If the DTM is baked it must be sanded with P400-P600 before topcoating."

I'm confused about this. When you say "topcoat" does that mean base/clear (i.e. some sort of color) or does that mean any kind of paint over (i.e. another coat of DTM)? I'm guessing any paint. So, it says it can be recoated but if longer than 24 hours you have to sand. What does baking the paint have to do with it? If sanding with 400-600, that sounds like color over the primer. I hate to overcomplicate things but I am confused!

Lastly, can someone confirm this is DuPont's best epoxy for what I want to do with it? I'll go look at their website and see if I can't figure this out myself. Big corporate websites are so tough to navigate though.

Thanks again, Scot
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Old 09-25-2008, 08:38 PM
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Quote:
Originally Posted by ScotY
Thanks, that helps a LOT!

Re. the chromate...it says "DTM is available in lead/chromate free ValueShade and chromate for use under body filler, polyester putties, primer-surfacers and topcoats." Is it safe to assume both types (with and without chromate) can be used under filler? I'm guessing that's true.
Use the chomate if that's what they suggest under polyester fillers

For recoatability, it says "DTM may be recoated at any stage of cure. DTM can be topcoated within 24 hours air dry without sanding the DTM. If the DTM is baked it must be sanded with P400-P600 before topcoating."

I'm confused about this. When you say "topcoat" does that mean base/clear (i.e. some sort of color) or does that mean any kind of paint over (i.e. another coat of DTM)? I'm guessing any paint. So, it says it can be recoated but if longer than 24 hours you have to sand. What does baking the paint have to do with it? If sanding with 400-600, that sounds like color over the primer. I hate to overcomplicate things but I am confused!
Baking the primer cures the primer faster so the recoat window without sanding is shorter. If you bake the primer then definately scuff it before recoating. If air dried the product has 24 hours that you can apply products without the need for scuffing. 400-600 is recomended for a final grit before sealer and paint-you can use coarser papers if you plan to reprime and sand again.

Lastly, can someone confirm this is DuPont's best epoxy for what I want to do with it? I'll go look at their website and see if I can't figure this out myself. Big corporate websites are so tough to navigate though.
I haven't used dupont epoxy in quite awhile but do remember their last DTM version was OK and reminded my of PPG's epoxy hybrids that are designed for use as a surfacer. Another good Dupont epoxy was Corlar but I'm not sure if they are carrying it anymore-check the industrial Dupont products. The DuPont Prime and Seal epoxy was not good at all IMO.

Thanks again, Scot
Hope that answers some questions, maybe a DuPont rep will chime in and answer. Or give one a call.
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Old 09-25-2008, 09:34 PM
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Finishing Coats are usually referred to as Top Coats.

I've not used the Dupont Brand, but I have used their Nason line Epoxy Primer/Sealer and found it worked very well.

And If you wait past the recoat window, you will have to scuff it for anything you put on top of it.

So...........
here is what I do:


After sandblasting or sanding to bare metal, I apply a good coat of Epoxy Primer to everything bare. Then within a couple of hours, I apply two or three coats of High fill eruthane primer. (High fill primer is a lot easier to sand than epoxy)
Once this has been done, I can take my time and do my body work. I will work one piece at a time, such as a fender or door or hood. I apply any filler right on top of the high fill primer, and block sand until straight. ( I keep applying high fill primer all during the process)

I plan my work schedule. If I work one or two fenders in the same day, and get them complete. (ready for top coat) and I know it will be several days before I get to work in the shop again. I will apply a couple of coats of High Fill primer. This will protect any bare metal areas from flash rust until I get to work on them again. I do this to all the body panels and set them aside in my storage building. When I'm ready to paint (top coat), I will sand all the body panels again with 600 grit. This also helps with removing any dirt/dust/finger prints. Wash all the parts with Dawn dishwashing liquid, dry, wipe with alcohol/water mix, tack and paint (top coat).
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Old 09-26-2008, 11:16 AM
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Thanks again, guys...great info! I'm pretty sure I'm equipped now to do this the right way!

I spent a couple of hours last night on DuPont's website. The DTM 25xxS was the only epoxy primer I found in the automotive refinish section so I guess I got the right stuff. I have to say, though, that for a major corporation, their tech sheets are full of vagueness (is that a word?) and typos. Very confusing trying to read between the lines and figure out what they are trying to tell you...especially for a beginner.
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Old 11-12-2008, 05:33 PM
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Got a new question...I applied the epoxy a while ago (directly over bare metal) and now I want to apply filler. I understand, from trying to decipher the tech sheets, that the only time you should apply filler without sanding if from 16-24 hours after spraying. I'm outside the 24 hours.

So, I'm thinking I need to sand or scuff before filler. The question is what grit sandpaper or is a red Scotchbrite enough? I don't want to sand through the primer as I wanted protection on the backside of the filler. What should I do?
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Old 11-12-2008, 08:22 PM
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scuff with 400
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Old 11-12-2008, 10:08 PM
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scuff with 80-120.
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Old 11-13-2008, 12:44 AM
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Hmmm...those are two pretty different recommendations. Not sure what to do?
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Old 11-27-2008, 02:46 AM
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I'm starting to think about the next steps...what would be the recommended Dupont 2k high-build type of primer to use over their DTM epoxy?

There are some areas where I'm thinking I will not strip to bare metal. Reason being, I did one fender and the original 20+ year old paint seemed pretty tough to remove and didn't seem in too bad condition. This was on the sides which, I assume, didn't get as much sun damage. The hood and roof need to be stripped and epoxied, no question about that...I'll strip and epoxy all the areas that need it, but there will still be areas with original paint. Do I need to epoxy over the old paint before the 2k primer?

I spent a while browsing tech sheets on the Dupont website and still can't figure out what the best primer is for me.
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Old 12-01-2008, 10:02 PM
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Is DuPont your only option?
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Old 12-01-2008, 10:41 PM
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Quote:
Originally Posted by matt167
scuff with 400
Or wipe it all off with a lacquer thinner soaked rag

Vince
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Old 12-01-2008, 11:11 PM
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Quote:
Originally Posted by baddbob
Is DuPont your only option?
No, I just thought since I don't really know what I'm doing, sticking with the same brand might be a good idea? I can't get SPI products...that I know.

I think most of the major brands are available locally. I called the shop I buy stuff from and asked about high-build primers. The guy, who I don't really think is very knowledgable, said they usually sell 7704 to the body shop guys over here. He also said they carry 7701S-7704S.

He also said I should just use the high-build on the areas that need it. Areas with "good" old paint can be left alone...then use 7740S sealer over the whole thing, right before paint. Is that good advice?

Thanks, Scot
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