PAINTERS & FLOW-CHECKS, How long to Sand?

Ok, I got the outside of my 39 body painted today, I have a few flow-checks in the clear, (damn that last coat ), anyway, how long do you wait to sand these out?

I want to wait until I get the car to a drivable state, a couple months or so I hope, but I don't want to wait until the clear is so damn hard that it won't easily sand out evenly.

On average, how long after spraying is "just right" in your experience to sand the boogers out?

 

depends on the clear and temp. on average i sand clear after 12 hrs. at anything above 75 degrees. it is sometimes a little soft yet but alot of water and soft pressure with 1500 or higher grit paper. i've also found for most flow checks a paint paddle cut down with paper wrapped around it helps to "block" the run out without getting you into the thinner clear next the run. good luck.

 

your pic just now loaded for me. that appears to be somewhat under your molding. i wouldn't worry much if any about the part that will definitely be covered by molding as the origin of the run tends to be quick to "rub through".

 

Thanks for the answer, it was hot today, like about 90, we got a rain so it is about 75 now. There is plenty of clear on the car so if I sand through I am a wanker X2....

I will make a hard block per your recommendation.

 

Unfortunately, I have a couple more heavy sags in more conspicuous places... Damnit....

 

It depends on the paint .On the can It will tell you buffing time .Stick with that ...Urethanes can be like a rock if you wait to long.......If its urethane 24 hrs .With 1500 or 2000 grit .

 

In my experience if you can imprint your fingernail in the run it's too soon. If you sand too soon you can get the run out but it will die back down after it's been buffed. I will often hit the run with some 600 wetsand paper just on the peak of the run to open it up and let it breath a little for a few days so it will dry faster and more completely. I also highly advocate using a cut down straight paint padle about 4-6 inches long wrapped very tightly with wetsand paper. I also try VERY hard to not let the sandpaper even touch either side of the run and only sand on the run itself. Good luck.

 

I wish there would have been a HAMB when I was 16, it would have saved me so many screw-ups....

VIVA la HAMB, Thanks for the answers, but give me more!!! I am like a HAMB sponge, dying to wick up wisdom!

 

depending on the brand and type of paint, overnight should long enough...if you wait too long urethane is like trying to buff cement.....use a paintstick as others have mentioned or a hard rubber block so you are snading only the run....after the run is smooth you can do an overall sanding to even out the peel if you want

 

The clear is DuPont Premiere, supposed to be top of the line crap that I bought nearly 2 years ago, (I am a little behind schedule )

I for sure will be cutting and buffing the whole car.

Too bad I got cocky on the last coat...

So the best answer might be to sand out the runs tomorrow then....

 

24hr.... no more then a week buffing will get to be a paint in the ass after that

 

if you hadn't got cocky, you might have had clear lay out "drier than a popcorn fart in a whirlwind" friend of mine's saying. he's a been a body man for 40+ years and had a hard time getting used to urethane clears.

 

I don't know much, but I do know I would rather have 15 runs as one dry spot....

 

amen to that 39. sounds like you've got it under control, now is when going slow and easy pays off.

 

I think 24hrs should be a good amount to wait depending on the temp.

 

I usually wait at least a week. In certain cases the clear is a bit hard, but you get a wayy better cut and buff that way. Keep in mind that a run is a builup of clear and will take longer to dry completely. You really don't want to start sanding it to find it goey in the middle. The dry times on tech sheets are usually for 3ish coats, think of the run as being at least 6...

Good luck. Use my tech for reference if needed... http://jalopyjournal.com/forum/showthread.php?t=367250

 

If air drying let get hard enough that you dont leave mark with finger nail. Take a single edge razor blade and put 2 layers of masking tape on each end leaving center of blade exposed and shave off most of run and block remainder of run and or curtain. This way you are working the sag and not so much the bigger area. Did auto body 25+ years and this little trick did work for me!

 

I actually saw a guy who got a giant run and just bombed on more paint until the run ran all the way down the panel and onto the floor. too late for this technique now though since you let it dry...

not saying this is a good idea, just reporting something I saw.

 

Smart , I like that.

 

They actually make a run "shaver" that does this same thing. It's cheap and easy to use too. I've done the same thing but it does take a touch of skill. I shave old pinstripes off the same way.

 

49ratfink, i've seen that myself. and heard about it alot more. i was painting a dirt track car several years ago, and after the first two coats laid on so nice i got thirsty and had a few beers waiting for it to tack before the last coat. needless to say the passenger rocker was well coated by the time i got the run chased to the floor.

 

Another trick to getting a run out is to take masking tape to it when it is still just a little wet. Fold the tape loosely between your fingers and lightly dap it into the edge of the run. Then put more clear over it. Trick is to get it at the right time. It's saved me a few times.

I like waiting as long as possible to sand runs. I may open them up early but it seems if you finish it off too early it seems to move and come back later. Sounds dumb but I've been able to see runs I thought were gone later on. It might be hard to see them but it the right light you can.
Clark

 

I have a subcription to that thread, and I have used reread it and put it to use a few times.

Thanks X2!!

 

That is funny, I have to admit that never crossed my mind.

I still have a silly grin on my face....

 

if its a decent "flow check" i wetsand with 320 till its almost gone, 600, then 1000, 1500,2k, then 3k. if u go fine, it will still leave behind a trace of it. u might think 320 is aggressie, but i can do it all day long on a 3 coat job and not burn. its the only way to get it flat and not round it off.

 

exactly the way i do it!! i have had people look at me so funny when im puttin that tape around a razor blade...

 

An other painter once told me, "if you don't get a few runs, you're not trying hard enough."

 

Look for as set of special sanding blocks called "RUN BLOCKERS" from a company called Motor Guard Corp. they are designed to sand only the highest point of the run, blocking it flat. Used properly, they will yield perfect results. And my experience has been if you sand that run too quickly, like sooner than a week or more, it will show up again as an indentation in the shape of the run. This is due to the differing cure rates of the the thicker paint on the run. I've sanded out runs the next day, and 2 weeks later, the run area was lower than the paint surface-it cured differently. Already mentioned is a trick to get the run to cure through, and that is to "break open" the run with 400g or 600g wet, just cut the top off, and then let it dry, it will help.

And, chasing a run off a panel is something I've done many times-let gravity work for you, chase it down the panel to the edge, then wipe it off with your gloved finger, or let it dry & razor off the buildup on the edge...cool trick if you can pull it off...

BUT, my experience tells me, let the paint DRY thoroughly before sanding the run out!! Good Luck!

Eric

 

I use the same process for the same reasons. I also have a run razor I use to open the top up and get it pretty low before I start sanding

 

Ok, got it cut to 1000 today.

The part above the drip rail was painted 6 days prior to today, the part below the drip rail was painted 3 days ago.

The 3 day old paint cut a lot easier than the 6 day, fortunately the 6 day old paint had fewer "mistakes" to start with.

Thanks for ALL of the comments here, I read every one and every answer allowed me to do a better job.

Now if I can just finish up without burning through....