Ready to block sand the seal questions
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AllGoNoShow
Promoted Users
Lizer,
Just curious- are you saying you don't use a true reduced seal coat? Just spray the epoxy 1:1 and wet sand to 600 and call it a seal coat? I have a few small parts I'm painting and eliminating the reduced seal coat would be helpful as I'm just putting base right over the epoxy.
Just curious- are you saying you don't use a true reduced seal coat? Just spray the epoxy 1:1 and wet sand to 600 and call it a seal coat? I have a few small parts I'm painting and eliminating the reduced seal coat would be helpful as I'm just putting base right over the epoxy.
Dave C 5
Member
I typically do what Lizer does . I spray a final unreduced coat of epoxy and sand with 400-600 grit depending on solid vs metallic. I gives me one last chance to go over it and sand out any scratches I didn’t get with the 2k primer . I make sure I get the base coat on by day 3 though. Have never had an adhesion problem . BUT - if you are doing any kind of stripes like on a hood or trunk you need to do a final reduced epoxy adhesion coat within 24 hours of base coat or to risk pulling paint when you remove the tape
I am at final block with 4 coats of primer. I am blocking at 150-180 now. It’s taking time since I am doing this in my “spare” time. I am trying to coordinate this transition such that the last thing I do is the night before is to seal it and then paint the following day (within 24 hrs) for a chemical bond (paint to seal coat).
The question I was interested in was getting from the 180 grit block. (Where I am at currently) to that final seal coat prior to paint if it’s been more than the 14 day window for a pure chemical bond.
The question I was interested in was getting from the 180 grit block. (Where I am at currently) to that final seal coat prior to paint if it’s been more than the 14 day window for a pure chemical bond.
Lizer
Mad Scientist
Yes—the primary reason sealer is reduced is to make it spray slicker. I don’t care about that because it’s going to be sanded anyway.
Jim C
Oldtimer
imo if your going to sand it then its not a sealer coat. its another round of primer. to me, sealer is a thin coat of epoxy or urethane sealer just prior to, maybe 30 min, base or color going down. if your blocking @ 180 grit then a full 1:1 coat like lizer said will be needed then sand that with 400 to get the 180 scratches out. after the 400 then then a quick reduced "sealer" coat just before your color is recommended. i believe this is what dave was referring to as an adhesion coat.
What’s the max safe window (time) between the 400 and sealer knowing you need 3 days cure to sand.
Jim C
Oldtimer
i think he said by the time he gets it sanded its not going to be fresh at that point. it will be well cured. in that situation then a fresh coat needs to go down. this way the epoxy wont be so chemical resistant that the base wont bite into it and lock on. the longer that epoxy sits the worse the adhesion will be. i have never had an issue with single stage or urethane primer adhering to sanded epoxy but basecoat.....all the time. you really cant let epoxy sit say five days, sand and spray base. the adhesion will be terrible. best adhesion will always be a reduced sealer coat 15-30 min before base.
Everything is a bit fuzzy here to me. I am not trying to call anyone out here. I am just trying to understand what I need at a minimum to do and not add unnecessary work steps.
Jim C. @Jim C your last post indicating that you can apply primer to an out of window say 600 prepared substrate would bond ok sounds great work flow wise for me. Would this still be a chemical bond if out of the 7 or 14 day window?
@Lizer good question. I am a novice here and can’t answer this definitively. However from my engineering background I would think the combination of a chemical and mechanical bond would be superior over just a chemical bond.
I appreciate everyone’s input on this thread.
Jim C. @Jim C your last post indicating that you can apply primer to an out of window say 600 prepared substrate would bond ok sounds great work flow wise for me. Would this still be a chemical bond if out of the 7 or 14 day window?
@Lizer good question. I am a novice here and can’t answer this definitively. However from my engineering background I would think the combination of a chemical and mechanical bond would be superior over just a chemical bond.
I appreciate everyone’s input on this thread.
dhutton01
Backyard Hack
Lot of overthinking going on here imho. Why not just follow the SPI datasheet? Reduced coat of epoxy as a sealer before base. Trying to keep all epoxy in its recoat window is good practice.
You’ll not get better advice than the advice from JimC. Visit his website for proof of that.
Don
You’ll not get better advice than the advice from JimC. Visit his website for proof of that.
Don
Thanks @Jim C So just trying to understand. If I have been sanding an epoxy primed surface lets say for a month down to 300-400. And I am happy and ready for base….
At this phase a fresh seal coat of epoxy reduced sealer just prior (30 mins for example) to base is acceptable. ?.
Jim C
Oldtimer
yes thats what your looking for.
epoxy can go over out of window sanded epoxy to refresh or restart your recoat window.
for your other question, i would not take epoxy that is say 14 days old, sand it with 600 and apply 2k primer over it. 600 is a bit too fine. typically if you took primer to 600 you would not be putting more primer over it. if you sanded that epoxy with say 180, then put 2k primer over it then that would be acceptable but i still think 14 days is too long. what i am saying is that 2k primer and single stage has better adhesion that basecoat does so poor adhesion on out of window epoxy will be less evident. in a nutshell, the longer epoxy cures then more chemical resistant it gets. the sooner you get something on it the better. its as simple as that. the 7 day window imo is too long. its ok for 2k primer and ss but not base. typically get a base on epoxy in no more than 36-48 hours and as said before, 30-60 min over a sealer coat of it is best.
Thanks @Jim C I do plan to shoot base/clear. So what it sounds like I need to do is going to stop sanding at 180. Shoot more epoxy primer to re-start the window. Sand to 400-500 (solid no pearl or metallic) within a few days and the seal and base clear right away. Makes sense to me. I’ll just have to dedicate the time and plan it so I can work within the all the windows while balancing the weather…..might need the big guys help on that part.
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Lizer
Mad Scientist
You can spot wet sand epoxy within a few hrs of spraying it. You could safely wet sand all of it the following day, so that will help your schedule. If I’ve wet sanded something I don’t spray anything else that day, so it can plenty of time to evaporate all the water off.
So with your example, if you want to spray base on Saturday, spray your epoxy on Thursday, wet sand 600 on Friday, and you’re ready for base on Saturday. If you want to do a reduced coat of epoxy you’d do that on Saturday as well. But if you get any nibs or imperfections you’ll need to give those a few hr to set up before you can sand them. After base, keep the car clean and out of the sun and UV except only to roll it out in the sun to check your base coverage, and then Sunday spray your clear.
I’d recommend activating your base with a capful of clear activator.
Try not to spray at night when the bugs are out, and you really want to see your base in natural sunlight before going to clear. You’re looking for light spots, metallic mottling, and striping. The typically inadequate booth lighting our homemade booths have usually don’t reveal all these imperfections.
So with your example, if you want to spray base on Saturday, spray your epoxy on Thursday, wet sand 600 on Friday, and you’re ready for base on Saturday. If you want to do a reduced coat of epoxy you’d do that on Saturday as well. But if you get any nibs or imperfections you’ll need to give those a few hr to set up before you can sand them. After base, keep the car clean and out of the sun and UV except only to roll it out in the sun to check your base coverage, and then Sunday spray your clear.
I’d recommend activating your base with a capful of clear activator.
Try not to spray at night when the bugs are out, and you really want to see your base in natural sunlight before going to clear. You’re looking for light spots, metallic mottling, and striping. The typically inadequate booth lighting our homemade booths have usually don’t reveal all these imperfections.
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Lizer thats great! That would save me a few days of waiting for it to dry enough to dry sand it. I am effectually slow at this not being a pro and that makes all these windows a lot of pressure. Wonder if it’s just me that feels that way.