Shrinkage

Dean

Dean

Promoted Users
Hey. New on here and first tine trying spi epoxy primer.
So im painting a 27 model a. Just a touch up here n there over old paint.
We striped the rear panel and did our body work over the existing priners and finish....and this is old skool nitrocellulose laquer for paint.
After filler was done we epoxy'd our repair areas with a 1:1 mix.
Sanded it all down in 600 wet. Any spots we burnt through i hit with same epoxy reduced 15% to be as a sealer.
Today i laid down my laquer paint. Everywhere edges of the epoxy are has bit in big time to show the line and sanding scratches.
Im new to old skool laquers and guy im doibg this for says its expected. Its not for me in my paint exp.
So is this an expected issue being so heavy in solvents in the paint?
Dam that epoxy is tough stuff to sand lol
 
Im at a loss here, so the only thing I can think of is maybe your talking about a spotted part of epoxy, and the solvent is showing mapping??
After 12 hours, the epoxy will laugh at lacquer thinner, so this has nothing to do with the lacquer paint.
 
how long was the epoxy allowed to cure and in what temp? remember epoxy is really temp sensitive. under 70deg it starts slowing the cure really fast until it goes completely dormant around 50. proper cure before paint would be 24hr at 70 deg +. that is surface temp not air temp
 
What do you mean "it's tough stuff to sand"?
Is it to gummy that it clogs the paper? which means it needs to cure longer
or not had enough activator,
or was the epoxy to hard? which epoxy should never be.
 
Barry said:
Im at a loss here, so the only thing I can think of is maybe your talking about a spotted part of epoxy, and the solvent is showing mapping??
After 12 hours, the epoxy will laugh at lacquer thinner, so this has nothing to do with the lacquer paint.
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Anywhere we didnt fully epoxy a panel, the feathered edges have bit in to show the line of primer. Was all wet sanded in 600.
 
Jim C said:
how long was the epoxy allowed to cure and in what temp? remember epoxy is really temp sensitive. under 70deg it starts slowing the cure really fast until it goes completely dormant around 50. proper cure before paint would be 24hr at 70 deg +. that is surface temp not air temp
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We were on our temps as required. And it sat a week through sanding process till topcoat. Primed last fri, sanded through the week and painted this friday
 
jcclark said:
What do you mean "it's tough stuff to sand"?
Is it to gummy that it clogs the paper? which means it needs to cure longer
or not had enough activator,
or was the epoxy to hard? which epoxy should never be.
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Didnt clog. I'd sand in 400 and would hardly do anything. Had to keep going back to cut orange peel out.
We used a house of colour epoxy on last project and was alot easier to cut.
 
Thats interesting about the sanding. Of all the epoxies i have ever sanded, spi is about the easiest. Its not like sanding 2k but for epoxy its pretty easy. Its been a long time since i ised hok on a daily basis but their epoxy if i am not mistaken is a hybrid. Its a high build epoxy meant to be used as a surfacer so not quite a true epoxy. Classified a little different.
The length of time you let it sit and cure was fine but the areas you spotted in after sanding, how long did those spots have to cure? While thing is very odd because in 20 years of shooting this epoxy i have never had edge mapping.
 
Jim C said:
Thats interesting about the sanding. Of all the epoxies i have ever sanded, spi is about the easiest. Its not like sanding 2k but for epoxy its pretty easy. Its been a long time since i ised hok on a daily basis but their epoxy if i am not mistaken is a hybrid. Its a high build epoxy meant to be used as a surfacer so not quite a true epoxy. Classified a little different.
The length of time you let it sit and cure was fine but the areas you spotted in after sanding, how long did those spots have to cure? While thing is very odd because in 20 years of shooting this epoxy i have never had edge mapping.
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It wasnt the small sealed spot that did this. It was on the 1 to 1 epoxy areas.
The sealer spots set overnight. They were find. No sanded edges on those
 
Dont know if the spots show. Toward left had epoxy. Then to right of the line was existing paint.
 

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Whatever it was it didnt show on any other of the laquers. Only on edges of primer. Sanded out today and 4 more coats and 1 spot cane back on a door. Others are fine.
 
Mapping is the answer, why?
Usually temp related from cold overnight?
But, never had my epoxy map and hard to sand?
Rather new to me, so I cant help.
 
Dont get this, temps were above 70 more than 2 days, we even tool day off to leave heat cranked in the shop.
As i finished my 3rd and 4th coat it all came back in same spots.
I put first coat on dry, was fine but showed on my door. Then on my 3rd coat it all came back on body of car too.
Not as bad but it shows. Isnt end a total fail being laquer and we have to sand n polish it all anyways.
From now on any laquer jobs id say im going to have to prime full panels to have no edges to bite in and show
 
What caused your line between the new and old is that you didn't feather out your repaired areas with course enough sandpaper. If it's body filler it will have sort of a "dropoff" line . Sort off like driving onto a newly paved section of road.
There isn't a smooth transition. Filler needs to be started with at least 80 grit in order to feather it out. And that is if you used a premium filler that will allow that to be done. The cheaper fillers won't allow you to start with 80 but you have to use 40 in order to block it properly. Priming over body filler or existing paint, the primer needs to be started wet sanded with at least 220 in order to level out everything. If not that may explain the difficulty in sanding you experienced. The smoother sandpaper won't bite deep enough to cut. I've used a lot of other epoxies in the past and spi is by far the easiest to sand. In fact it is the only primer I use. I've got every color except the red oxide. Once I figured out the benefits of spi epoxy I quit using everything else. Hope this helps.
 
elwood said:
What caused your line between the new and old is that you didn't feather out your repaired areas with course enough sandpaper. If it's body filler it will have sort of a "dropoff" line . Sort off like driving onto a newly paved section of road.
There isn't a smooth transition. Filler needs to be started with at least 80 grit in order to feather it out. And that is if you used a premium filler that will allow that to be done. The cheaper fillers won't allow you to start with 80 but you have to use 40 in order to block it properly. Priming over body filler or existing paint, the primer needs to be started wet sanded with at least 220 in order to level out everything. If not that may explain the difficulty in sanding you experienced. The smoother sandpaper won't bite deep enough to cut. I've used a lot of other epoxies in the past and spi is by far the easiest to sand. In fact it is the only primer I use. I've got every color except the red oxide. Once I figured out the benefits of spi epoxy I quit using everything else. Hope this helps.
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Prob spots are nowhere near the filler. Probably a foot or more away in some spots.
Used 3m fillers, cut with 80gr. Finished in 180. Feathered any edges back in 320 to prime, exsiting paint got sanded in 320 on full panel before priming.
I sanded epoxy once dried in 400 first was the hard to sand issue i guess. Personaly if my choice i dont epoxy over my body work. I use it on metal only. Id cut other primers in 400 so is why i started this primer in that grit.
Like was mentioned above, the other house of colour isnt a true epoxy as this is.
 
I have always accused lacquer related products as coming back to life when you start scuffing them. Had lacquer based bondo spot putty soften a ton of work. Not really sure about old school lacquers other than I thought you could buff them endlessly, like years and years, so my backwards thinking would be to let the lacquer do whatever it does to seal itself after you scuff it. Maybe its overnight, maybe its days, dont know, but I would tend to think in that direction since its the line that has the issue.
 
anotheridiot said:
I have always accused lacquer related products as coming back to life when you start scuffing them. Had lacquer based bondo spot putty soften a ton of work. Not really sure about old school lacquers other than I thought you could buff them endlessly, like years and years, so my backwards thinking would be to let the lacquer do whatever it does to seal itself after you scuff it. Maybe its overnight, maybe its days, dont know, but I would tend to think in that direction since its the line that has the issue.
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It is a finiky paint to use. Personaly i hate it and see why its a thing of the past.
Its always moving being non activated and only reduced, or thinned. It did settle down a bit when i walked in yesterday after sittibg overnight. Hope its not to bad today when i go to work.
I point to the paibt being the issue and is what it is. It will be fine once sanded out for polishing.
Just thought maybe someone had issue similar and a solve for it other than having to epoxy full panels if using old school laquers
 
What I imagine happened is the edge was lifting the lacquer, and not the epoxy. Thinner softened the lacquer, swelled the scratches, and didn't soften the epoxy. Two different materials next to each other tend to do that, especially something as different as lacquer and epoxy.
 
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