Scratch Shrinkage Problem

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strum456

Oldtimer
I am trying to figure out what I have been getting sand scratch shrinkage or swelling lately.


Example one:

1999 Acura Ingegra
I blocked the OEM paint with 180 and sprayed 2 coats of SPI epoxy. I always induce my epoxy more than 30 minutes. I probably waited an hour between coats. The car sat in the sun for at least one day before I blocked it again with 180. I sprayed 2 more coats of epoxy, sat in the sun, and blocked again with 180. Then I sat the car in the sun for a week. I used one coat of Turbo for the final session. After a day in the sun, I lightly blocked it with 220, then 320. After another day in the sun, final sanded with 400 and 600.

On the roof of this car, if I look close enough I can see what appear to be 180 scratches all over it! Only guys like us would see this kind of thing, but it really irritates me and I want to figure out what I am screwing up.

I have another example where I can see what I think are a few 80 grit scratches. I finished my filler with 180 and quickly went over it with 320 before using epoxy. Maybe I missed an 80 grit scratch somewhere? I didn't guide coat on that step. Same thing though, this part saw plenty of sun before painting. Sun in between steps, and atl east a week before final paint. I used all epoxy on this, so I was spraying it wet for build. I never rush flash times. A lot of the time I just do one coat, 2 at most.

Thanks guys.
 
Sometimes it's because the substrate was able to absorb and hold solvents from the primer long enough for the primer to become solvent resistant, which traps solvent under the ever more impermeable layer of epoxy. Once the solvent finally escapes, the result is mapping, shrinking, and the revealing of sand scratches. This is a terrible problem in collision repair because of the compressed time frame. Part of the way we deal with it is to have paint and featheredges sanded with very fine paper like 320 with a non-directional pattern (no block marks, just DA marks). Usually OE paint does not present problems, but I have seen exceptions.

It could possibly be that your coats are going on a bit too wet, which encourages solvent trapping.
 
My guess??!!??
Being roof and considering how we paint roofs, its possible solvents were trapped in one of the products and if the solvents set on a sanded substrate, they can take a 600 scratch and make it look like a 180 or even 80 grit.

Just a guess on my part, not knowing all the info.
 
I spray inside, but I usually move my parts out into the sun shortly after spraying. Would putting the parts in the sun too soon cause a problem like this? I don't normally wait very long - about the time it takes to clean my gun. Obviously, there is something wrong with my process. I THOUGHT that I was taking my time, and following best practices.

Would this have anything to do with using epoxy for build? I know epoxy is slow, and I thought I was accounting for that. Maybe not enough? I just want to get to the bottom of this before my next project.
 
i dont put stuff in the sun for a day or two. imo you kick the surface too fast and trap solvents.
 
1999 Acura Ingegra
I blocked the OEM paint with 180 and sprayed 2 coats of SPI epoxy. I always induce my epoxy more than 30 minutes. I probably waited an hour between coats. The car sat in the sun for at least one day before I blocked it again with 180. I sprayed 2 more coats of epoxy, sat in the sun, and blocked again with 180. Then I sat the car in the sun for a week. I used one coat of Turbo for the final session. After a day in the sun, I lightly blocked it with 220, then 320. After another day in the sun, final sanded with 400 and 600. judging by the process all looks OK IMO, did you apply a sealer? what did the basecoat look like after it flashed off-any scratches showing at this stage? I wonder what the build thickness was on that coat of turbo if you made it from 220 to 320 to 400 and 600?

On the roof of this car, if I look close enough I can see what appear to be 180 scratches all over it! Only guys like us would see this kind of thing, but it really irritates me and I want to figure out what I am screwing up.

I have another example where I can see what I think are a few 80 grit scratches. I finished my filler with 180 and quickly went over it with 320 before using epoxy. Maybe I missed an 80 grit scratch somewhere? I didn't guide coat on that step. Same thing though, this part saw plenty of sun before painting. Sun in between steps, and atl east a week before final paint. I used all epoxy on this, so I was spraying it wet for build. I never rush flash times. A lot of the time I just do one coat, 2 at most. It's really important to apply filler tightly to the surface-good pressure and release of air pockets most importantly on the first swipes-I don't know if this is the situation here but I've seen where filler wasn't applied right over coarse grit scratches and because of the inconsistencies or air entrapment the scratches sometimes show themselves after some heat cycles.

Shrinkage sucks, the cure times are long on most of my projects-I can't take a chance. Some OEM paints can really pull in solvent, I've seen many times where a repair halo shows up after full cure and even on a nicely featheredged OEM paint the ring shows up right there when the rest of the solvent comes out. How long has this car been painted now?
 
I finished the car in mid-July. The OEM paint pulling in solvents would make sense. I've never seen anything like this - I have a consistent X pattern of scratches all over the roof and some on the truck lid. I can't see anything on any of the vertical surfaces. The hood was a new aftermarket hood. It looks great.

I always thought spraying epoxy wet was a good thing (I don't want to bridge scratches with dry spray). I probably hosed it on the horizontal surfaces a little too much and the OEM paint sucked in the solvents. I guess I should have sanded the OEM paint with a finer grit than 180.


There is another project I did recently that is showing some shrinkage or swelling after a few weeks time, but it looks different. There is one area where there are several scratches together, and there is another single scratch by itself in another location. I can't see anything on the rest of the panel. These scratches appear to be larger (coarser grit) than the ones on my Acura roof. A couple of the scratches don't even look like they could have been created by a normal sanding motion. They, kind of randomly zig-zag (no I didn't use a board sander). Most are just straight line scratches though. No chances or short cuts (that I know of) where taken on this panel. I didn't spray over anything coarser than 180, and most times I even smoothed out the 180 scratches with 320. The only thing that I may have rushed is sunning the panel.
 
Yes, putting heat on the panel too quickly can trap solvent. Together with a very wet first coat and fairly coarse scratches in the OE paint, it all may have set up a "perfect storm" of solvent trapping and subsequent shrinkage.

SPI epoxy is almost magic, but it's still a solvent borne coating and bad stuff can happen with substrates that can absorb solvent, be they OE paint, filler, or old lacquer. This is why we typically see our best results on panels that have been completely stripped.
 
strum456;30815 said:
There is another project I did recently that is showing some shrinkage or swelling after a few weeks time, but it looks different. There is one area where there are several scratches together, and there is another single scratch by itself in another location. I can't see anything on the rest of the panel. These scratches appear to be larger (coarser grit) than the ones on my Acura roof. A couple of the scratches don't even look like they could have been created by a normal sanding motion. They, kind of randomly zig-zag (no I didn't use a board sander). Most are just straight line scratches though. No chances or short cuts (that I know of) where taken on this panel. I didn't spray over anything coarser than 180, and most times I even smoothed out the 180 scratches with 320. The only thing that I may have rushed is sunning the panel.
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Same procedures used on this other project?
 
Bob Hollinshead;30820 said:
Same procedures used on this other project?
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Not exactly. This was stripped to bare metal. I sprayed 2 coats of epoxy an hour apart. I kept the piece inside overnight and skimmed the whole panel with filler the next day (it sat for at least 24 hours).

I cut my filler with 80. I used some dolphin glaze here and there and blocked everything with 180. I believe I did a quick pass with 320 too.

I sprayed 1 coat of epoxy and set the panel in the sun for an hour. I took the panel in, allowed it to cool and shot my second coat. Then I put it back out in the sun for the remainder of the day and then next morning. I positioned the part to get sun all morning, and I blocked it around noon with 80, then 180 and 320. After another hour or so in the sun, I cooled the panel and sprayed another coat. I sunned it for an hour and then shot the second. Same process - the next day around noon, I blocked it with 180 - 320, sunned it for an hour, sprayed 1st coat, sun for an hour, and sprayed coat 2.

I repeated the above process until the panel was straight. I used black epoxy for build and gray epoxy as guide coat. After everything was straight, I laid the panel outside for a week before a final blocking with 320, then 400 and 600 wet.

I used prospray black base. I sprayed one coat in the morning. Went to our farm during the day, and sprayed coats 2 and 3 an hour apart that evening. The next day I sprayed 4 coats of clear, 30 minutes apart. One day later I put the part in the sun all day. the next day I sanded it with 400, and sat it out 2 days.The 3rd day I sanded it with 600 and then flow coated with 2 coats, 30 minutes apart.

FEEL FREE TO SHOOT HOLES IN MY PROCESS GUYS. I WANT TO LEARN!
 
im new here and been looking over some forum posts , seems to me like many guys on here seem to really pile the materials on , epoxy has its place in the refinish world , i have only used it over bare metal for superior adhesion and corrosion protection , its from my knowledge that epoxy is not sandable and see where guys are using it to build by spraying 2 coats on heavy and from what i been told 1 coat stay open to top coat body work or prime for 7 days and multipal coats more than double the top coat window so in theory by spraying 2 heavy coats of epoxy then 2k multipal times repeating the process your trapping solvent thats trying to escape from the epoxy so if the top layers like base coat , clear coat dry faster it would cause lifting swelling or many other issues , shrinkage and sand scratches tell me solvent is escaping and thats when u see the scratches appear
 
lethalcx;31262 said:
im new here and been looking over some forum posts , seems to me like many guys on here seem to really pile the materials on , epoxy has its place in the refinish world , i have only used it over bare metal for superior adhesion and corrosion protection , its from my knowledge that epoxy is not sandable and see where guys are using it to build by spraying 2 coats on heavy and from what i been told 1 coat stay open to top coat body work or prime for 7 days and multipal coats more than double the top coat window so in theory by spraying 2 heavy coats of epoxy then 2k multipal times repeating the process your trapping solvent thats trying to escape from the epoxy so if the top layers like base coat , clear coat dry faster it would cause lifting swelling or many other issues , shrinkage and sand scratches tell me solvent is escaping and thats when u see the scratches appear
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Welcome to the SPI forum!

While your point about piling on material should be well taken, it might be best for you to gain some experience with SPI epoxy before making generalizations about its use. There are similarities and differences between SPI epoxy and other epoxy brands. A few of the finest restorations known to this forum have been achieved using only SPI epoxy for priming and surfacing. It is sandable, and sands rather nicely, too, when worked within the proper time frame.
 
Explain the problem with the shrinkage ? This isn't the only post I saw with the same issue
 
lethalcx;31265 said:
Explain the problem with the shrinkage ? This isn't the only post I saw with the same issue
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Too much material too fast is generally the cause. Your point about "piling on material" is absolutely correct. But some of the info in your post about epoxy in general doesn't apply to SPI epoxy, and there is a low tolerance on this forum for the expression of opinions that show a lack of experience with the material in question. I encourage you to use SPI epoxy for yourself for a few months and then speak from the knowledge gained that way, instead of making generalizations based on the use of other products.
 
crashtech;30845 said:
Frankly, I'm stumped.
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None of this makes any sense as he has done everything perfect and over-killed every step, so now that leaves one thing not covered and perhaps the only answer????
Dry spraying and bridging, Turbo not wet enough on first coat?
Base not wet enough on first coat?
Epoxy, I have never found that that matters how you spray it, once it sets, its done.

Strum, what do you think?
 
lethalcx;31272 said:
So spi epoxy in theory is also a high build primer ?
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SPI epoxy can be used to achieve build, but it is not a high-build primer. It is sandable, remains extremely tough and flexible even at higher film builds, and gives excellent isolation (solvent barrier) once cured.
 
The theory that I sprayed the epoxy too wet over relatively coarse scratches on the OEM paint sounds like the most likely culprit. I could be accused of spray too heavy in many cases, but really don't think that dry spray could be a possibility.

Barry, what is the official rule on sun after spraying. Can I set parts in the sun immediately after spraying epoxy or turbo with no potential harm? I have always gone to great lengths to expose my parts to as much sun as possible between steps. Could I be doing more harm than good?
 
setting outside right away will trap solvents . i let epoxy or whatever set 24 hrs before going outside .
 
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