Question
After an outsourcing relationship went bad, I had to do a white and black gloss job on four small pieces. I tried to do the job with Target Coatings products, then ICA 2k waterborne polyurethane. I was not able to get a satisfying polish with either product. I cannot get rid of the sanding marks. I have tried many types of sandpaper, compounds and pads without success.
Any advice? For level sanding, what kind of paper, compounds, and pads work for you?
Forum Responses
(Finishing Forum)
From contributor D:
For pads, start with wool and finish with foam - first orange foam, and finally black foam. For compounds, use Menzerna 2L, Paste 16 and if needed 106FA.
It has been my experience that you should let the finish cure some more after leveling, before the final polish. The marks could be from the finish still being too soft. Waterborne takes a long time to get hard.
Do your leveling with wet sanding. Start with the 800 grade sandpaper and go to 1200. When you buff, start with a white colored pad and end with the foam buff pad.
At one time wood finishers had the opinion that an auto finish was too brittle, difficult to apply, difficult to sand, difficult to polish, and difficult on the pocketbook. Not so any longer. By the time a wood finisher has applied a traditional wood finish, then waited and waited and waited, our counterparts around the corner are getting ready to polish their automobile coating.
When you add up all the waiting and the labor and the down time and the other numbers that enter the equation, the bottom line is that all that wasted time is money you haven't made. I think the application of auto finishes can cross over and become beneficial to us wood finishers.
No, it doesn't look like painted glass, but it is glossy, though a little wavy. I am trying to find a way to do a good enough finish when painted glass is not possible. I cannot put my mental health at risk each time a customer "needs" a gloss finish.
1) Use whatever primer you like. Polyester works well.
2) Bury the thing in acrylic urethane clear coat. With acrylic urethane, there is no thickness limit, but you have to be careful about shrinkage and solvent pop, so you have to let it flash between coats and wait a day before you start polishing. Here in Arizona we set stuff out in the sun where it will get to 170F. Acrylic urethane loves heat, the more the better.
2) After you've got on about three coats of clear, you level the surface with P400 grit paper. The best way to do this so that the object gets the flattest is with a long DuraBlock and file board paper, and hand block it.
3) If that ain't cutting it, using a hard and perfectly flat DA pad and an 8" Mud Hog (National Detroit 900) or equivalent. You use P400 stearated paper to get the thing as flat as possible.
4) Back into the booth for two more coats of clear. If you're doing this right, things should look really good at this point. Clear goes down on flat sanded clear much better than it does on raw material or primer. If you're really good and have a great booth, the off the gun surface at this point might be good enough.
5) Start with P800 6" 3M 260L finishing film on a 3/32" random orbit sander (I like AirVantage but Dynabrade or Hutchins is fine) and flatten out the urethane wave again. Once again using a hard DA pad.
6) Move up to P1200 3M 260L finishing film and go over the P800 and make sure you've removed the P800 scratches. Use a soft DA pad. 3M calls these Painter's Pads.
7) Next we use P1500 3M Trizact Clearcoat finishing discs wet (spritzer bottle) on the same random orbit with a soft DA pad.
8) We're looking really shiny now.
9) Next we use P3000 Trizact moist (spritzer bottle) on a large throw DA (3/8") with the soft pad and we're looking shinier still. 3M recommends the large throw on P3000 Trizact as it speeds the process up and since Trizact is used wet, there isn't the threat of pigtail scratches that exist during dry sanding. I use a $29.95 C-H sander from Wal-Mart for this operation as it has the big throw, it's cheap, and it works.
10) Rotary buffer time. Wool pad and Menzerna 2L. This gets rid of any stray pigtail scratches (which will be there, trust me).
11) Wool pad and the Paste 16. You're near mirror surface at this point.
12) Black or orange foam and P106FA and it's sunglasses time.
I've done this for decades and there is no other way to achieve this level of perfection. If shiny and wavy is good enough, you can skip sanding steps, but you'll see the difference.
1) Two coats of primer
2) 3-5 coats of top coat
3) Polishing with foam pads, 360-1000
4) Buffing with 3M compounds
My problem is with the drying time on the top coats. I'm having to wait 5-7 days before I can polish, before my fingernail doesn't leave a mark. I lay down 3 coats, wait 24 hours before another 2 coats. At 3 coats, the polishing goes to the primer. Thicker coats require more drying time. I've tried a clear coat of lacquer after the three, but I'm still at the drying time. I'm at my wits end. I'm limited to one brand of automobile NC here in Mexico. I'm thinking that I should go back to Dupont acrylics which I tried several years ago and had problems with, but perhaps their formulas have changed since then.
