Epoxy/filler/featherfill poly primer

I wonder how that gun compares to my prolite 2.5. I usually go 3-4 coats. Depending on how tired I get. Lol. But I see people blocking from 120-400 and barely breaking through in areas so maybe the sata is more of a fire hose.

And I have done 80 alot and then went to 2k in the past....lots of cure time and usually end up with a few rounds of 2k. But haven't done it like that in quite some time.
 
orangejuiced86 said:
I wonder how that gun compares to my prolite 2.5. I usually go 3-4 coats. Depending on how tired I get. Lol. But I see people blocking from 120-400 and barely breaking through in areas so maybe the sata is more of a fire hose.

And I have done 80 alot and then went to 2k in the past....lots of cure time and usually end up with a few rounds of 2k. But haven't done it like that in quite some time.
Click to expand...
I measured the nozzle as best I could to be 2.7 mm. Typical Sata under rating.

77B6B9C5-A30C-47E6-81E9-877E6712098E.jpeg


Don
 
So... I guess there is some contention about what grit is safe to prime over. Back in "the good old days," I was taught to finish body filler with 80 and prime it with lacquer primer, an easy to use product, but it's "reversible," and can be dissolved by solvent even after it has dried. This is an old-skool production method and does not have good long term results, since the lacquer has lots of solvent and shrinks drastically into the 80 scratches down the road. Not only that, when it gets painted, it absorbs solvent like a sponge and releases it later over time, magnifying the effect of any big scratches it had been laid on top of. Eventually a lot of us learned to use finer grits before primer, especially in the production environment where cure time is limited. That's the most extreme example, and you could say that it doesn't apply to modern material, but read on.

Nowadays almost everyone uses some kind of catalyzed product like 2K urethane primer that has less solvent and activates to become "non-reversible," no longer dissolvable by solvent. This helps a lot, but still, most 2K primers are permeable to some degree, and while not technically "reversible," they will still absorb a certain amount of the solvent that is applied over them. So they can still swell and shrink, and can still show deep scratches below under certain conditions. I have seen this numerous times, in bodywork and in featheredging of existing finishes that wasn't done finely enough. Cure time helps this problem, but a lot of work is stored inside with cool temps, so problems can remain dormant for a surprisingly long time.

Any material that uses solvent to make it thin enough to spray is subject to potential shrinking and swelling, at least for a time, even epoxy. As we know, epoxy cures slowly, and in its partially cured state, it can and does absorb solvent. This is why you must wait 48 hours to apply poly primer on epoxy, for some reason poly seems to soak into epoxy very aggressively. In a worst case scenario, some of that absorbed solvent can remain down in the bottom layers of the job and only fully evaporates months later, and if coarse grits have been primed over in this example, there will be sand scratch mapping or worse.

In my opinion, just based on observation, if there have been solvents trapped in a job, but finer grits have used throughout, there is a much better chance that the job can be saved with sunlight and a sand and buff. If too coarse of grits have been used, this becomes less possible, maybe impossible with a metallic because the metallic will map into the scratches and be visible no matter the smoothness of the clear.

This is my thinking on the matter, and why I don't like to see primer going over coarse grits. I'm sure not everyone will agree, and maybe I am at least partially wrong, I'm ready to learn and edit this post as necessary!
 
crashtech said:
So... I guess there is some contention about what grit is safe to prime over. Back in "the good old days," I was taught to finish body filler with 80 and prime it with lacquer primer, an easy to use product, but it's "reversible," and can be dissolved by solvent even after it has dried. This is an old-skool production method and does not have good long term results, since the lacquer has lots of solvent and shrinks drastically into the 80 scratches down the road. Not only that, when it gets painted, it absorbs solvent like a sponge and releases it later over time, magnifying the effect of any big scratches it had been laid on top of. Eventually a lot of us learned to use finer grits before primer, especially in the production environment where cure time is limited. That's the most extreme example, and you could say that it doesn't apply to modern material, but read on.

Nowadays almost everyone uses some kind of catalyzed product like 2K urethane primer that has less solvent and activates to become "non-reversible," no longer dissolvable by solvent. This helps a lot, but still, most 2K primers are permeable to some degree, and while not technically "reversible," they will still absorb a certain amount of the solvent that is applied over them. So they can still swell and shrink, and can still show deep scratches below under certain conditions. I have seen this numerous times, in bodywork and in featheredging of existing finishes that wasn't done finely enough. Cure time helps this problem, but a lot of work is stored inside with cool temps, so problems can remain dormant for a surprisingly long time.

Any material that uses solvent to make it thin enough to spray is subject to potential shrinking and swelling, at least for a time, even epoxy. As we know, epoxy cures slowly, and in its partially cured state, it can and does absorb solvent. This is why you must wait 48 hours to apply poly primer on epoxy, for some reason poly seems to soak into epoxy very aggressively. In a worst case scenario, some of that absorbed solvent can remain down in the bottom layers of the job and only fully evaporates months later, and if coarse grits have been primed over in this example, there will be sand scratch mapping or worse.

In my opinion, just based on observation, if there have been solvents trapped in a job, but finer grits have used throughout, there is a much better chance that the job can be saved with sunlight and a sand and buff. If too coarse of grits have been used, this becomes less possible, maybe impossible with a metallic because the metallic will map into the scratches and be visible no matter the smoothness of the clear.

This is my thinking on the matter, and why I don't like to see primer going over coarse grits. I'm sure not everyone will agree, and maybe I am at least partially wrong, I'm ready to learn and edit this post as necessary!
Click to expand...

Sounds logical to me. Very astute reply.
 
Well stated Crash.

I think everyone misunderstood my post as I was only referencing my first round of sanding poly primer. As I stated, I treat poly primer like body filler and my goal is to get the panels straight and flat. I like and use 80 grit for this purpose, however I go over everything again with 180 grit to refine the scratches and feather any edges.

Sorry for the confusion but it did generate a lot of good information being posted. ;)
 
crashtech said:
So... I guess there is some contention about what grit is safe to prime over. Back in "the good old days," I was taught to finish body filler with 80 and prime it with lacquer primer, an easy to use product, but it's "reversible," and can be dissolved by solvent even after it has dried. This is an old-skool production method and does not have good long term results, since the lacquer has lots of solvent and shrinks drastically into the 80 scratches down the road. Not only that, when it gets painted, it absorbs solvent like a sponge and releases it later over time, magnifying the effect of any big scratches it had been laid on top of. Eventually a lot of us learned to use finer grits before primer, especially in the production environment where cure time is limited. That's the most extreme example, and you could say that it doesn't apply to modern material, but read on.

Nowadays almost everyone uses some kind of catalyzed product like 2K urethane primer that has less solvent and activates to become "non-reversible," no longer dissolvable by solvent. This helps a lot, but still, most 2K primers are permeable to some degree, and while not technically "reversible," they will still absorb a certain amount of the solvent that is applied over them. So they can still swell and shrink, and can still show deep scratches below under certain conditions. I have seen this numerous times, in bodywork and in featheredging of existing finishes that wasn't done finely enough. Cure time helps this problem, but a lot of work is stored inside with cool temps, so problems can remain dormant for a surprisingly long time.

Any material that uses solvent to make it thin enough to spray is subject to potential shrinking and swelling, at least for a time, even epoxy. As we know, epoxy cures slowly, and in its partially cured state, it can and does absorb solvent. This is why you must wait 48 hours to apply poly primer on epoxy, for some reason poly seems to soak into epoxy very aggressively. In a worst case scenario, some of that absorbed solvent can remain down in the bottom layers of the job and only fully evaporates months later, and if coarse grits have been primed over in this example, there will be sand scratch mapping or worse.

In my opinion, just based on observation, if there have been solvents trapped in a job, but finer grits have used throughout, there is a much better chance that the job can be saved with sunlight and a sand and buff. If too coarse of grits have been used, this becomes less possible, maybe impossible with a metallic because the metallic will map into the scratches and be visible no matter the smoothness of the clear.

This is my thinking on the matter, and why I don't like to see primer going over coarse grits. I'm sure not everyone will agree, and maybe I am at least partially wrong, I'm ready to learn and edit this post as necessary!
Click to expand...
I completely agree when the primer being referred to is urethane 2K. In my experience poly is a completely different animal. I also view it as sprayable body filler. You can get away with a lot of backyard hackery using poly. That’s why I use it on all my backyard hack restoration work. It’s also why Corvette resto shops use a lot of it. I only use urethane 2k to refine fine grit scratches before sealer.

Disclaimer. I use Z-Chrome Rust Defender poly exclusively. Never used anything else.

Don
 
So Don you're basically telling me I need to use poly on these '70 truck bedsides.

But poly is such a PITA. It sure would block amazing once I receive Dean's blocks though.
 
Poly is different. But certain precautions still must be remembered, since it is still a solvent-borne material until it's fully locked up and the solvent evaporates. This has to be kept in mind for people that might be applying it up onto existing paint featheredges or on top of any material that can absorb solvent. You'd be shocked at how often someone can read something like "poly is fine on an 80 scratch" and then think they can do something wacky like scratch up an old existing finish with 80 and poly prime it. No, you can't do that!
 
Think he needs to get some Guide Coat.;)
Those would be 600 gt on my slot body's.
Hell, 600 is my 80. More like 40 because I went to 800 because.
Actually going Small has taught me quite a bit about this paint stuff that never got my attention on full size. Little 'things do have a Big impact and realize the Importance of Patience!
 
Since you guys are just offering free education....


When prepping for poly would you

1. Block epoxy with 180 and spray poly
Or
2. Block epoxy with 180, spray a wet coat of epoxy, wait 48hrs and spray poly.
 
RosharonRooster said:
Since you guys are just offering free education....


When prepping for poly would you

1. Block epoxy with 180 and spray poly
Or
2. Block epoxy with 180, spray a wet coat of epoxy, wait 48hrs and spray poly.
Click to expand...
You could do either, though it's a bit of a catch-22, meaning if you could block with 180 without hitting metal, you probably didn't need poly, and if you block and hit metal, you need more epoxy anyway.

I tend want to do a little sanding no matter the circumstance if time allows, since every application of primer is an opportunity to leave it where it belongs and remove it from where it does not. But there's a fine line and you don't want to go to far if you don't want to take a step back again.
 
crashtech said:
You could do either, though it's a bit of a catch-22, meaning if you could block with 180 without hitting metal, you probably didn't need poly, and if you block and hit metal, you need more epoxy anyway.

I tend want to do a little sanding no matter the circumstance if time allows, since every application of primer is an opportunity to leave it where it belongs and remove it from where it does not. But there's a fine line and you don't want to go to far if you don't want to take a step back again.
Click to expand...
I think I'll do both! Block 180, spot epoxy any bare metal, then poly...
 
After 2-7 days spraying epoxy, and planning on spraying poly, I won't bother sanding. Bare metal will set me back another 2 days. After 7 days epoxy, I block with 180, spray 1-2 coats of epoxy, then 48hrs spray poly.
 
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