Flow coating. What's your method?

Brad J.;n74198 said:
When doing 3-4 coats I can usually still finger print the next day. 2 coats never a problem.

After you guys are done with the second round of clear are you starting out with 400 for you cut and buff? I usually do the 4 coats followed by 800 up wet and I never go through the clear. I'm blocking with 12" durablocks and rolls of 800/1000 grit paper before I switch to the sheets of finer paper and a soft block. I'm a little uncomfortable getting 8 coats of clear on sharp body lines or panel edges.

Now if I get an occasional run or sag and have to 400 the panel and start over then I suppose I flow coat but my cut and buff is the same procedure so it doesn't look any different than 4 coats and a cut and buff.
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I was wondering the same thing Brad. I'm trying to understand this process. How does 8 coats of clear work over sharp edges and body lines? And aren't you defeating the purpose if you start blocking with anything less than 400? If you are trying to get rid of the "urethane wave"? Personally I've sprayed stuff with 3-4 coats, wet sanded with 600 then gone back with 3 more and wet sanded with 800-1200-2000-3000 trizact and 5000 trizact and been happy with the results. I know what JimC said but I've never noticed any urethane wave after blocking it with 800 then moving on with the finer grits.
 
When doing 3-4 coats I can usually still finger print the next day. 2 coats never a problem.
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That finger print is not in the clear, this is normal with most clears as its the solvents leaving the print as they exit.

Are they still spraying this as a heavy wet coat typical of uv clear or maybe just medium wet? I'd be afraid of being in run city spraying that way.
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Yes spray just like the others, I just have not seen evidence that the retarder increase running more then a small perfect from my playing with it, eve though you would think it would.

Also barry would maybe waiting more than a day before blocking prior to flow coating maybe stop some paper clogging or is the clear reaction pretty much over with? I know it is still off gassing for quite a while but had always assumed at around the 24 hour mark the majority of the reaction was complete?
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In a case like you ask, time is always on your side, a day in sun a week in shop, can only help, there are just to many factors involved with all of them changing things to say for sure and exact time.
SCFM, Gun set up, Air at gun, How many coats, Air flow, Activator vs Temp, Color of base even plays a role as well as brand.
 
The 5th coat with retarder is worth trying in my opinion.

I'm not sure what I think of the flow coat method unless your going really aggressive on the cut and buff. Otherwise a lot of extra work for the same appearance. I've worked on too many old restos/auction cars that show what a lot of material build up will do. You get huge chips on the edges of doors and such.

Maybe the next junk door I get I might play with it a little and see what kind of film build up I get.
 
I've done the 320 dry blocking before the flow coats numerous times and have never had a problem, I was skeptical at first-always concerned about limiting the chances for any shrinkage problems.... but as usual Barry was right. Sure saves time and easy to see your progress vs. wetsanding with a finer grit.
 
Chris_Hamilton;n74204 said:
I was wondering the same thing Brad. I'm trying to understand this process. How does 8 coats of clear work over sharp edges and body lines? And aren't you defeating the purpose if you start blocking with anything less than 400? If you are trying to get rid of the "urethane wave"? Personally I've sprayed stuff with 3-4 coats, wet sanded with 600 then gone back with 3 more and wet sanded with 800-1200-2000-3000 trizact and 5000 trizact and been happy with the results. I know what JimC said but I've never noticed any urethane wave after blocking it with 800 then moving on with the finer grits.
Click to expand...

You can cut wave out with finer grits like 800 or 1000 no problem if the right block is used, if you use a coarser grit you can use a softer block and get the same results.
 
well we have 2 things going on here. if your just going to cut and buff then starting with 800 or 1000 is great but if your flowcoating and blocking between coats then 400 cuts things nice and flat. urethane wavy increases the more coats you put on and of course how you spray has alot to do with it as well but considering if you flowcoat your probably looking at a total of 6-8 coats then the 400 makes a big difference.....usually
 
I agree with Jim but would add that I watch that I don't put much if any pressure down on the block when sanding, the paper will create suction and create it's own pressure when you push and pull on the block. I can feel the texture of the finnish transfered thru the block and when it starts to feel smooth then I wipe dry to see where I'm at. I will finnish with 6-800grt going in a different direction. Once I see only the scratches in the last direction I did then I call it done and ready for the next step.
 
yes if your wetsanding i totally agree. the suction will make it just follow the waves. i usually just block dry so i didnt think to mention it.
 
I looked at my wet blocks again. I have 5 16" durablocks that I have blocked flat on a surface plate with 320 grit paper. I use that many because once they get wet the paper won't stay on. I use these blocks with 1000 or 800 Klingspor wet paper. My wave is gone but if I pull out my 3m sheets and a 6" soft block then they don't remove the wave, only the orange peel.

I'll experiment with it in the future. See how many coats and how durable the edges are. This is an informative post.
 
This is why I use a piece of Oak on the first go when wet sanding clear.
Its about 1 1/4" wide and 5" long x 3/4" thick and I work a 12" square area at a time until flat and orange peel free.
Not saying its the best way, just what I have been doing and why. I think the dry sanding method is worth a try and may be much quicker.

I plan to try the method outlined by Barry next time around.
 
For a 6" soft block I have one of the original 3m 2sided blocks (now 3m stopped making them) soft grey sponge on one side and firm rubber on the other, the best made the ones available now are not even close so I watch how I use it. I also use a 9" hard rubber block made for dry block sanding bondo orange in color. You have to be careful not to leave them in water because they all will warp overtime and that could get you into trouble with lines showing from the block ends.
 
thought i would share my minimal experience with retarder a year ago i had a cowl panel for a 69 nova i restored and didnt want to cut and buff because they are a pain so i put 3 heavy coats of universal on back to back no flash 5 % retarder it looked dipped and matched the rest of the car that was cut and buffed 400-5000 just saw it a week ago and still looked perfect yesterday i thought i would try 25 % ret and put two coats on a hanging panel w extended flash that was a bad idea even a med wet coat wouldnt hang i kinda figured that but i had to try

also thought i would add my block of choice is 3/4 in sch 40 pvc cut in different lengths hard on fingertips but i like the results
 
Thanks Justin, that's good info, like I said yesterday, I'm learning on this also as to new of a product.
 
Justin, did you have the 5% retarder in every coat on the Nova hood or just the last?
I am really into this dipped look thing and want to give it a try without have to go through a long learning curve.
 
sure did 5 % every coat today i did 3 coats on some hanging flat panels first 2 coats 5 % 3rd 10% hung on good looks great still flowing hopefully not too far south LOL
 
Okay guys, I just painted the flow coat round of some fenders. Prepped as normal, 4 coats uv then blocked at 400 dry with a hard block. I then sprayed 3 coats untampered uv and on my 4th I mixed retarder at 30%.

I did have a run but it's where the fender changes directions (not uncommon for me) and I had a spot with a touch of very light orange peel.

The run is all on me, the orange peel is also on me I got spooked because the clear wasn't doing its usual lay down when I started (I don't know how to explain, that nasty heavy peel look it gets when it's heavy enough that just lays down when you are a foot or so past it) so I punked out and increased travel speed and viola peel.

Other than that it does look fantastic.
 
Back in the 80's when I was doing acrylic enamel paint jobs I would add a lot of retarder
to my last coat, (like 25 to 50% of what was left in the cup) I would just
mist it on and all the paint would just level out and all melt together.
You can use retarder in place of reducer, slow it way down and it won't run
like over reduction with reducer. But you have to keep it clean, it takes forever to dry.
Works real good for large surfaces that are difficult to keep a wet edge on.
I learned this trick from a painter that painted school busses.
 
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