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  #4231 (permalink)  
Old 04-25-2018, 09:33 AM
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Quote:
Originally Posted by cowboy_dan View Post
I'm seeing what looks like grey epoxy on the body, red epoxy underneath, and I think I remember you using black epoxy some time back.
Any particular reason for using those colors where you did?
The short answer is no. I started out with gray and switched to black to paint the frame and misc parts. I then bought red thinking it would not show the rock chips so much on the bottom of the floor pans.

SPI puts UV protection in all there epoxy so it is strictly a matter of choice. Personally, I will probably stick with the black or red.

There is some lodgic in putting one color on the bare metal and then using another color over it so when you are blocking you can tell when you are about to sand through. I can not tell you that has been my practice though. If it was I would have started with gray or black and put the red on top under the color coat to help hide chips.

One other consideration is some paints are somewhat translucent. Metalics for example. If I were painting the car a light metalic color I would go with the gray or white to prevent shadows in case of poor coverage from the base coat. Many modern finishes require a specific primer color under the base,

This dark red SPI base covers so well, it is a non issue here.

John

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  #4232 (permalink)  
Old 04-26-2018, 07:33 PM
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Trying to get the firewall mudded before my 7 day window expires. I just am not getting the basement time I would like.

If I have to re-apply the epoxy it won't be the end of the world I guess.

John
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  #4233 (permalink)  
Old 04-26-2018, 08:22 PM
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You have to sand the epoxy to re-apply, so wouldn't it be the same to just sand what's there and apply the filler over that ?
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  #4234 (permalink)  
Old 04-26-2018, 10:36 PM
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Quote:
Originally Posted by Too Many Projects View Post
You have to sand the epoxy to re-apply, so wouldn't it be the same to just sand what's there and apply the filler over that ?
I have heard that arguement made and I am sure people do it, but it is not what SPI or PPG either one recomend in their tech sheets. Both recommend sanding and recoating after 7 days. The reason, as I understand it, is because the epoxy looses it's ability to chemicaly bond after it has cured for 7 days.

Would it be OK to scuff with some coarse paper, like 180 and apply filler? That would be a good question for Barry.

John
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  #4235 (permalink)  
Old 04-27-2018, 03:48 AM
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I would scuff with 80 grit.

It was my understanding, a scuff and bondo apply was fine. Should stick just like applying to bare metal which we know works extremely well.

Let us know what Barry recommends.
There is no way I will ever have patience enough to work in a 7 day window.
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  #4236 (permalink)  
Old 04-27-2018, 03:48 AM
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"The epoxy does not need to be sanded before applying body filler (up to 7 days)."

That just means sand before filler if past a week. Sure, scuff with 180 if it is. No need to reapply. If you do reapply, keep "If time allows, its always best to apply filler over epoxy after it has set for 24-48 hours." in mind.

Reapplication doesn't only have to do with being open to non-sanding application of the next layer of material. It is mentioned, in PPG's case, to assure that at least a certain thickness of epoxy (required so the product can perform as intended) remains on the panel. When used properly, scuff sanding can leave less primer than that. Since SPI is an epoxy primer-surfacer, 3 coats is probably plenty of material left after a 180 scuff. Do that and keep rocking. What you did is like putting on an extra coat of clear because sanding it flat is anticipated. If you have big sand-thrus, a shot of epoxy there might be wise.

My .02. Lookin good, John
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  #4237 (permalink)  
Old 04-27-2018, 06:15 AM
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Quote:
Originally Posted by John long View Post
I have heard that argument made and I am sure people do it, but it is not what SPI or PPG either one recommend in their tech sheets. Both recommend sanding and recoating after 7 days. The reason, as I understand it, is because the epoxy looses it's ability to chemically bond after it has cured for 7 days.

Would it be OK to scuff with some coarse paper, like 180 and apply filler? That would be a good question for Barry.

John
OR the SPI forum...
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  #4238 (permalink)  
Old 04-27-2018, 08:37 AM
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I just hung up from Barry. He did not disagree with what you guys are saying but did suggest that it was a gray area that could depend on several different variables. Cleanliness, prep of cured epoxy, time involved, etc.

The bottom line was to make sure it was hand sanded well with at least 180 grit and watch very carefully how the filler feathers into the epoxy. If there is any sign that the filler is not feathering in smoothly, re-coat with epoxy. If you can get the filler on within the recoat window, you have both a chemical and mechanical bond. If you sand and re-coat beyond that time, you are relying on a mechanical bond only.

I have to admit, talking to him did take a little pressure off me on this firewall area. He is a remarkable guy.

John

Last edited by John long; 04-27-2018 at 08:45 AM.
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  #4239 (permalink)  
Old 04-27-2018, 10:39 AM
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Quote:
Originally Posted by John long View Post
Cleanliness, prep of cured epoxy, time involved, etc.
If you can get the filler on within the recoat window, you have both a chemical and mechanical bond. If you sand and re-coat beyond that time, you are relying on a mechanical bond only.
John
And a mechanical bond is ALL every body person relied on since the inception of Bondo.
How many of your past restorations are still around with 20 year old paint and filler that isn't falling off and you applied that filler to bare metal ?? You KNOW how to prep and clean a surface before applying a filler. The only thing new here is the theory of 2 chemical agents being able to bond if put in contact in a certain time period. Is that better than the old way ?? most likely but it certainly hasn't become the "only" way to do it now.
I'm with ya on wanting this to turn out as the best restoration you've ever done, but I feel like you are stressing yourself out over a job you already know how to do, and do very well...
Carry on with whichever route you decide to take.
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  #4240 (permalink)  
Old 04-27-2018, 04:23 PM
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I never wiped over unsanded anything myself. I believe the only benefit in doing so is being able to apply only the minimum number of coats of epoxy recommended for best product performance, resulting in a material cost reduction vs applying more so the film can be sanded and remain thick enough.
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  #4241 (permalink)  
Old 04-27-2018, 07:01 PM
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Quote:
Originally Posted by idrivejunk View Post
I never wiped over unsanded anything myself. I believe the only benefit in doing so is being able to apply only the minimum number of coats of epoxy recommended for best product performance, resulting in a material cost reduction vs applying more so the film can be sanded and remain thick enough.
I have to admit, I also scuffed the epoxy. That is why I put the third coat on. I just have a hard time wiping filler on shiney epoxy. Even if it is only 36 hours old.

John
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  #4242 (permalink)  
Old 04-28-2018, 05:35 PM
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The only part I can't figure out is how come a fellow like yourself ain't complaining about sanding at all. I suspect you either retired from being the sandman, or have an arrangement with him where you get to sleep in a chair in the basement while he throws sand at whatever you want sanded.
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  #4243 (permalink)  
Old 04-28-2018, 07:17 PM
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Quote:
Originally Posted by John long View Post
I have to admit, I also scuffed the epoxy. That is why I put the third coat on. I just have a hard time wiping filler on shiney epoxy. Even if it is only 36 hours old.

John
Let me set your mind at ease John. First off forget about the window and rushing, getting the filler on before it closes, just completely forget about ever hearing about it. listen (read) carefully, ALL that is, is saying that you dont have to sand if you dont feel like it, if done within whatever the window is, Thats it. So ANY bodyman that cares will sand with at least 180 before recoating OR filler,whether its 1 day 2 days or a thousand days, as long as its cured enough to sand without it balling up, your good, so throw that out the window.
Anyone doing an all epoxy job or an epoxy sandwich job shouldnt be in a drag race anyway, so take your time, you rush and you'll start saying good enough or the battery will cover it, so get that window out of your head and just sand it all with 180.. Why 180 you say?.... Well epoxy fills the 180 scratches so all you do is 320 over that and paint. sanding with 80 and the scratches will be to deep to do that so you'll have to prime ,sand with 180, prime .then sand with 320. Your doing great, just stop trying to drag race and rush when theres no reason too. This window thing is getting out of hand for No reason, Who in there right mind would NOT sand before putting something on top of something else? Well, not ME but the verdict is still out about my state of mind so it matters little. So just start off sanding it edge to edge with 180 then go ahead and do what you want to do, it wont take much time at all to sand it, first, do your filler work (putty work) prime it and sand it again. minor imperfections like you have should be done in a finishing putty like ez sand that sand easily with 18o. even the good fillers dont sand as well as the putty with the 180 you shouldn't have to touch anything on that fire wall with 80 at all.

Think of a paint sealer. You wouldnt ever use a non sanding sealer (I hope no anyways). You would want to use a sandable sealer because even though you dont have to sand it, it always comes out better if you do, you find a piece of trash here and a little peel thats not quite slick enough, You know what I mean. In my whole 40 years I've never NOT sanded my paint sealer. Also I have never recoated or put filler on on anything that wasnt sanded first, Not ever. Dont try to skip such an important step and get the filler on without sanding, whether it CAN be done or not, who cares, take your time and do what you know is right.
BTW, way filler sticks better when sanded than what not window or not.
How do I know this you ask? 40 years of putting it on and sanding it off tells me. ALWAYS,ALWAYS,ALWAYS sand before putting anything on top of anything if you the best adheasion.
This window thing is a non issue and absolutely no more time should be wasted on it or worrying about it. just 180 sand it the same way weve always done it. Its also a good way to know for sure if the epoxy is cured or not if its not cured it balls up on your sandpaper quick. if theres any balls at all its not completely cured and nothing should be put on top (yes, you can put filler on top of uncured epoxy and get away with it) but its not the best way for best results. so why do it unless you dont care about doing a great job. Then why use epoxy in the first place?
Im just trying to set the record straight on this stupid window thing everyone is so concerned about, I hope I did that.

This goes out to everyone,

One more time, STOP worrying about the window and sand the dam thing first, Always. Its the right way and its the only right way.

Last edited by deadbodyman; 04-28-2018 at 07:27 PM.
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  #4244 (permalink)  
Old 04-28-2018, 08:55 PM
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Thanks guys. I have been running all day. Just catching up. I appreciate all the input.

BTW, I am a little unique. I just love to sand. I can spend hours in the "zone" blocking out a quarter panel

Scuffing or prepping??? Not so much.

John
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  #4245 (permalink)  
Old 04-29-2018, 06:15 AM
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Let me add one more thing about a chemical bond. When it comes to rust pits that cant be sanded properly that chemical bond (The stupid window thing) sure comes in handy so if you have the pits epoxy them and fill them within the window ,EZ sand works great on pitts but good fillers can used too if they're wiped clean and theres not too much excess filler left on then sand with 180. its the best way to take care of those nasty pits. Theres other instances where normal sanding isn't possible so that window does come in handy sometimes.
Keep in mind, a chemical bond is what the factory relies on and weve all seen those white cars with the paint peeling off and the green epoxy showing haven't we. THATS a chemical bond that's failed.

Last edited by deadbodyman; 04-29-2018 at 06:27 AM.
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