Yes I have searched; I just can't find the answer. I am currently working on my '62 Olds 88. I have finished all fabrication and welding of patch panels, all metal "finishing" (I am still in the learning phase) and have cleaned, prepped and painted the bare metal (and filler...hence still learning) with one seal coat of epoxy primer and 4 coats of high build primer. HERE is my basic question: Can I apply sealer & paint to properly sanded primer even if some of the primer was sanded over a month ago? The paint shop told me I will have to re-scuff any primer that has sat "too long" in order to reopen the pores, or paint won't adhere. My main problem is I cannot block sand this car all at once, given my day job and quality family time. I currently am about 1/6th done with blocking, with delays as I realize panels aren't as straight as I thought. Now this worry tailspins into questions like these: If I must re-scuff the entire car just before painting, can I use fine Scotchbrite and just lightly cover by hand? Will hand scuffing minutely ruin the flatness of the surfaces? Do I really need to scuff again anyway? The paint lady said I would risk adhesion problems if I haven't recently sanded before paint. So now I imagine that final blocking is professionally done all at one time, right before painting. Am I too paranoid? Here's the '62
I think if you go over the car with a gray scuff pad just before you spray it you'll be fine. As long as you don't press down hard with your fingers while scuffing, you will not effect the flatness of the primer. The gray scuff pads are equal to about 600 grit paper. So I wouldn't use anything courser than that. Sent from my iPhone using TJJ app
I work the same way, one panel at a time and it can take me several months before I make it around the car. Once it is all blocked and ready to go spray a reduced coat of epoxy before your basecoat. Your basecoat will stick really well to that. What grit are you using for your blocking?
Thanks guys! I also wondered what grit the gray scuff pads were (like if it was fine enough) and you answered my question! OK, I will give the entire car a quick scuff 24 hours or less before painting. Thanks!
My blocking is 400 grit, hopefully that is close to proper. It sands nicely for me. Areas where I sprayed the build primer super thick I resort to 220 and then back over with 400.
Can I add a question to this thread? If you put a coat of sealer over the finish sanded primer, are you stuck with the look of the dried sealer? If the sealer shows orange peel can you sand that out? Just wondering why some finished paint jobs have an orange peel look under dead flat areas if you look at just the right angle. Bob
Sealer can be sanded after a while. But that is not typical. Is is designed to be a "wet on wet" product. Usually when I see what you are describing is because the painter used the wrong reducer and it flashed off too fast, or because he may have applied it to slow and therefore it went on too heavy, or wet. The base coat can do the same thing though. Too heavily applied, drying too fast because of the wrong reducer being used. Then they clear it, sand and buff it. The clear looks awesome, but if you look under it, peel everywhere.
Not picking on anything you are saying specifically. Everything else you said is spot on. But I hear that all the time, even from the 3M reps. But take a grey pad in one hand and a piece of 600 hundred in the other. Rub them in between your fingers and tell me they even remotely close to each other. Personally I stay away from scotch pads. Sand paper sands, scotchbrite pads scratch.
What color are you going to paint the car? Are you planning on using a sealer of some kind? If it is going to a metallic color over the 400 it is most likely too coarse. We always prep the cars with 800 before paint. If your using a sealer 400 is usually OK. Usually you see that on light metallic colors. What you are seeing is the the base coat has ended up with too much surface texture either from the way the base coat was sprayed or the surface it was sprayed over was not totally smooth. Could be a sealer that was too orange peely or the primer not sanded smooth enough.
Back to my original question (I'm making sssloooowww progress!) with more confusion: After slowly blocking a car, must I still scuff all of the previously sanded areas again if it has been more than 24 hours since the last time that area was sanded? It feels like a never ending job. I finish blocking flats of front fender, start blocking top of fender the next week. After that is nicely finish sanded, I still have to re scuff anywhere I previously sanded before I can add a spot of primer or seal the car before painting? I realize why you must topcoat within the window shown on the paint lable. I also realize that after that window of time (usually 24 hours on 2k primer surfacer) is over, you must mechanically abrade the surface so topcoat will stick. I THOUGHT this would mean that if the surface is sanded, it is...well...sanded. And doesn't need re-scuffing if I wait another day, week or month since the mechanical scratches are why the topcoat will stick. Do paints always release solvents and "open up" upon FRESH scuffing of the surface, and that's why they will adhere, not just because there is a surface to bite???
Once the primer is sanded you don't need to sand it again before paint. However you do need to make sure it stays clean and free form any kind of contamination before it gets painted.
So why not block your panel, then seal coat of reduced epoxy and let it sit. The skin on the epoxy will seal and protect your surfaces primer from contaminants and moisture absorption till you are ready. Same with the next panel and on around your car. You can even work more on top of the epoxy if you see something's you don't like. When your painting weekend comes, scuff the seal coat, or give it a final blocking and apply another coat of reduced epoxy and paint it. - Now that cellulite looking paint is just awful and on all but the most well prepped surfaces and perfectly laid base coats. Oh yea, none of that on a cut and rubbed solid color single stage.
Amen on working a spot and epoxy, work a spot and epoxy... Don't throw sealer down until ready to paint.
Very good point on keeping it clean. So why does the paint store say I will still have to scuff right before painting, to "re-open the pores" of the sanding primer?? After the original 24 hour window, is paint ONLY going to stick mechanically? And if so, I should not have to re-scuff like your post (which gives me hope!) says. Maybe they meant "re-open the pores" because of dust built up over time (sanded surface not kept totally clean)?? Or is there still some sort of chemical bonding that happens??
After the window, its all mechanical. But Every product is different and that might make the difference in information you are getting. Best to follow the tech sheet for the product and not what people say- ( most of the time lol)
Not to pick at anything that anyone has said I am seeing some pretty good advice here, but I would not blow color over 400 grit sanding, I would go at the very least 600 grit and would prefer it to be smoother than that.
I was sanding my truck for a quick coat of primer, it wasn't going fast enough. Nephew Phil came by, and said "Hang on...let me make a call"...about 5 minutes later, his pal LeRoy rolled up. Leroy got out and said, "Mike, start up there, drivers side...I'll meet you at the back!" It took over an hour, and LeRoy wasn't about to take the 20 dollar bill. I forced him. LOL Get a pal to help! Lotsa guys in your neighborhood might have experience, or would be quick studies. Just emphasize CAUTION. (and cash)
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