epoxy

danp76

danp76

Oldtimer
HI guys, I'm finishing up the welding on some floor pans on a car project. The entire car body was blasted and put into epoxy and is on rotisserie. Do I need to sand the existing epoxy with 180 and reapply epoxy before skimming with glazing putty? I'm talking about the underside/floors of the car that has some minor pits in the metal. The epoxy is a few years old but always been indoors in shop. I"m guessing I have to sand, epoxy and then apply glazing putty? thanks guys!
 
I think I need to reapply epoxy. I don't think I can apply glazing putty over sanded epoxy that's a few years old. What's safe to apply over clean epoxy that's a few years old, but always inside? Only new epoxy?
 
danp76 said:
So essentially, nothing will stick to cured sanded epoxy except for new epoxy?
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Within the seven day window, you have a chemical bond with the epoxy. After seven days that ability is gone. If you sand it, you will still have a mechanical bond. Many production shops would do that but most high end or restoration shops will not.

Applying glazing putty over year old epoxy would be like placing it on top of bare metal. If you sanded it well, it may not fall off but it is not the preferred way. If you are going to the trouble to do a rottissorie restoration, sanding it and re-epoxying it would be effort well spent.

John
 
danp76 said:
Thanks guys, I was hoping to avoid all that extra sanding, but I guess I need to.
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Dan, You absolutely would have to sand it no matter what you did. Without sanding it and it being a year old you would have a desaster on your hands.

The extra epoxy will give you a little build and a better base. You will be glad you did it.

John
 
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Thank you Texasking, I'll look into it. I was going to sand the epoxy, but wasn't positive if I needed fresh epoxy over it ,before glazing putty, urethane primer, etc.
 
I was about to ask a similar question on this topic, taking it a little farther. First of all, as a hobbyist, getting anything done within 7 days is rarely possible.

I prepped some fender inner panels with the intent of leaving them in epoxy for about a month, then finish coating them. What I noticed is that after sanding with 180 or 220, I can still see those scratches ghosting through after 3 more coats of epoxy.

This left me scratching my head. If every time I quit for more than a week, then I have to sand with 180. Then apply 3 more coats, block out with 180 again to get a flat wave-free surface, then resume with 220/320/400 before top-coating. And that has to get done within another week?

I don't have time to finish them now. But, I don't want to waste material for 3 more coats and sand it out again.

Moving on, I will be coating the insides of the fenders with SPI bedliner. However, it will be about 3 months of cure on the epoxy by the time I have everything ready to coat with bedliner. I suppose I will have to sand again with 180, then spray more epoxy, then coat with bedliner?

I am probably over thinking this.
 
I guess products wouldn't stick to sanded cured epoxy, only new epoxy will stick to sanded cured epoxy?
 
danp76 said:
I guess products wouldn't stick to sanded cured epoxy, only new epoxy will stick to sanded cured epoxy?
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I think it would be more correct to say products like polyester glazes and fillers 2k (urethane) primers will "stick" but not as well as if they were applied over epoxy that is within the re-coat window. By applying them over cured, sanded epoxy, you lose one of the major benefits of epoxy which is superior adhesion. It wil stick much like applying glaze to a sanded OEM finish.

MX442 said:
I was about to ask a similar question on this topic, taking it a little farther. First of all, as a hobbyist, getting anything done within 7 days is rarely possible.

I prepped some fender inner panels with the intent of leaving them in epoxy for about a month, then finish coating them. What I noticed is that after sanding with 180 or 220, I can still see those scratches ghosting through after 3 more coats of epoxy.

This left me scratching my head. If every time I quit for more than a week, then I have to sand with 180. Then apply 3 more coats, block out with 180 again to get a flat wave-free surface, then resume with 220/320/400 before top-coating. And that has to get done within another week?

I don't have time to finish them now. But, I don't want to waste material for 3 more coats and sand it out again.

Moving on, I will be coating the insides of the fenders with SPI bedliner. However, it will be about 3 months of cure on the epoxy by the time I have everything ready to coat with bedliner. I suppose I will have to sand again with 180, then spray more epoxy, then coat with bedliner?

I am probably over thinking this.
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I think you may have confused things a little. When we talk about the re-coat window for epoxy it means the re-coat window to apply something like body filler, glaze, or 2k primer, over unsanded epoxy. If you are blocking with 180 and stop for a couple weeks, month etc. just resume blocking. If you have blocked it and need to reapply more as long as it's sanded you are fine. The 180 scratches provide mechanical adhesion for the old epoxy to bond with the new. If you have somewhere you have not sanded and it's past the window then you would need to sand it with 180 before re-applying. Barry recommends 180 grit as the preferred grit to sand epoxy with before reapplying epoxy because it is the best comprimise between a good scratch and too deep of a scratch that will compromise what you have already done. Make sense?
If you are worried about any little low area etc that is unsanded before applying epoxy, simply use some red scotchbrite and scuff those areas.
 
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I should try an adhesion test on cured, "old" epoxy sanded with 180 and glazing putty over it vs. "fresh" epoxy with glazing putty over it. Have you guys tried this test?
 
Chris, I get that, but not exactly what I'm asking. (I have a hard time typing what I'm thinking). I get stalled out before the point of applying the final "glamour coats." I'm getting everything finished out with epoxy and then it will sit for weeks to months. I want to resume by doing a 600 wet sand and apply final finish. If I start over with 180, I am going backwards. Then I feel like I'm wasting product to build up and bury 180 scratch.
 
I think MX442 that you could lightly sand your epoxy that has been sitting with 400-600 if it's ready for paint, and apply epoxy as a sealer.
 
MX442 said:
Chris, I get that, but not exactly what I'm asking. (I have a hard time typing what I'm thinking). I get stalled out before the point of applying the final "glamour coats." I'm getting everything finished out with epoxy and then it will sit for weeks to months. I want to resume by doing a 600 wet sand and apply final finish. If I start over with 180, I am going backwards. Then I feel like I'm wasting product to build up and bury 180 scratch.
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You can resume with whatever grit you are sanding with. The 180 grit is mentioned because it will allow maximum adhesion over the cured epoxy. That doesn't mean that if you stop i the middle of sanding with whatever grit you have to 180 and reapply.

Maybe this will help (maybe not:)) It applies whether you are doing only epoxy (I think you are) or if you are blocking with 2K urethane or Poly.
Ideally you want to do all your "correcting", blocking (bring up lows, work down highs) in a grit no coarser than 180. Block and reapply till you have all your lows brought up and any highs worked down. to the point you would consider it straight. Then you would re-apply 2-3 coats of epoxy (or 2K or poly). At this point you are no longer correcting but are now leveling what you just applied to fill in any 180 scratches and to refine the surface to prepare it for your final finish. I sometimes do this starting with 220 using my blocks (especially if you applied 3 coats) or 320 using my blocks (done more if I applied 2 coats). I guide coat it cause that's what I'm used to and block it. It goes quick doing it with 220 and I don't use much if any pressure. After 220, I'll go over it again with 320 on my blocks to remove the 220 scratches. Little to no pressure. Once that is done, I switch to more flexible/smaller blocks and hand pads and do a final sand with 600 wet. At this point you are not correcting at all, just refining and removing the 320 scratches. Once I go over it, it is done. Ready for sealer then paint. Using epoxy for your sealer anywhere from 1:1:25% to 1:1:50% will give you excellent adhesion to your surface.
So do all your correcting in no finer than 180 grit. Then apply your final coats, which you will then level and refine the surface. If there is any doubt as to whether or not you have the body straight after the 180 step, you should not apply your final coats and proceed with the finer grits. Get it straight in 180 grit.

Obviously we are talking about high end refinishing, this doesn't really apply to collision repair or lower end jobs. Hope that clarifies things a bit.
 
Thanks Chris. I'm over worrying about this. Yes, I have only done epoxy so far. (Inner fenders, under the hood, etc).

On the Cadillac, we are at 9 days since spraying epoxy, and still not done putting filler on the epoxy. Following the 7 day rule, we would be applying epoxy every week. Outside the 7 day window, how long is it safe to sand with say 150, and apply more filler? Or do we need to hit it with 180 and spray another coat first?

Again, thanks for helping.
Chris_Hamilton said:
Maybe this will help (maybe not:)) It applies whether you are doing only epoxy (I think you are) or if you are blocking with 2K urethane or Poly.
Ideally you want to do all your "correcting", blocking (bring up lows, work down highs) in a grit no coarser than 180. Block and reapply till you have all your lows brought up and any highs worked down. to the point you would consider it straight. Then you would re-apply 2-3 coats of epoxy (or 2K or poly). At this point you are no longer correcting but are now leveling what you just applied to fill in any 180 scratches and to refine the surface to prepare it for your final finish.

This is where I'm getting hung up. It sounds like you do this daily and stay within the re-coat window. You might get it from this stage to finish within a week. It sounds like you resume with 220 and finish it out quickly. For me it will be months. By the time I will resume with 220-600 will be after the previous coats have sat for months.

I sometimes do this starting with 220 using my blocks (especially if you applied 3 coats) or 320 using my blocks (done more if I applied 2 coats). I guide coat it cause that's what I'm used to and block it. It goes quick doing it with 220 and I don't use much if any pressure. After 220, I'll go over it again with 320 on my blocks to remove the 220 scratches. Little to no pressure. Once that is done, I switch to more flexible/smaller blocks and hand pads and do a final sand with 600 wet. At this point you are not correcting at all, just refining and removing the 320 scratches. Once I go over it, it is done. Ready for sealer then paint. Using epoxy for your sealer anywhere from 1:1:25% to 1:1:50% will give you excellent adhesion to your surface.
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