Streaky Lacquer Problem

      Pros troubleshoot a case of striping and streaking in a post-catalyzed lacquer job, and discuss how to fix the finish. October 18, 2005

Question
I am doing a faux French polish with pore filler and post cat lacquer. My finisher was using the wrong tip (Binks "1310" instead of "0910") and there are very visible streaks. The streaks are from uneven coats, which is really a gloss problem. Here is the question - can I rub out the finish (I have enough DFB) to eliminate these streaks, or will this always telegraph through no matter what I do? Do I have no choice but to strip and re-do? The finish is already flat and level - really, the problem is in the topcoat (35 deg sheen).

Forum Responses
(Finishing Forum)
It sounds like the streaks are micro bubbles and you are asking if they can be sanded out. Is that right? If so, hope you have a strong arm, since it may take quite a bit of sanding to remove the bubbles. If it is in the topcoat alone, you may luck out, but since lacquer re-wets itself, this may go deeper than the last coat.



From contributor D:
Is the 35 sheen the shiny streaks or the dull in between? And what sheen are you going for?


From contributor S:
If your dry mil thickness is thin enough, then all you need to do is scuff sand the whole top with 320 grit and lay down another finish coat. If you think that you have no room to play with on your dry mil thickness, then your sanding goal is not just to scuff sand, but to grind down enough finish so that you can - again - lay down a final finish coat. That finish coat will be your money shot. How much sanding you need to do is determined by your coating weight, which is measured in dry mils.

Do the math: check the percentage of solids by volume of your coatings materials, including any sealer coat materials you used, factor in how much you reduced each coating, and multiply it out by the wet mils which you shot.

For example, if your container has 20 ounces of only one finish material which was 20% solids by volume unreduced, and you added 15% (3 ounces) reducer to your mix, you now have 23 ounces of a mix that is 17% by volume. Shoot that reduced mix so that you lay out 4 wet mils and it will cure to about 2/3 dry mils (4 X 17% = 0.68 ≈ 2/3). If your total coating weight requires a dry mil thickness of 4 dry mils, then that means that you could shoot 5.9 passes, each 4 wet mils (6 passes if you do some good scuff sanding between each pass) and when all is said and done, you have 4 dry mils (4 0.68 = 5.88).

Anyway, scuff or grind down some finish and shoot a new money coat. Overlap each pass by at least half. I do not know what "DBF" is, but maybe this has something to do with elbow grease?



From the original questioner:
I do not need to calculate wet or dry applications. We are a small custom shop. There are no micro bubbles. The streaks are the lines, 2" - 4" wide in alternating patterns and alternating between the 35 deg sheen and a flat sheen (like blushing). This is a result of my finisher not paying attention to what he is spraying (normally he does a fantastic job -I have no intentions of firing him, just a stern, short lecture on paying attention to what he is doing). Stripping and redoing will cost me all of my profits and more. The streaks were caused by a fluid tip with a larger opening than necessary, and this caused a heavier stream on the outer portions of the fan. It looks like alternating gloss pattern. I am shooting for the 35 deg sheen (db) I am using. I just want to know if I can hand buff/polish with increasing grits to achieve a consistent gloss or if am I wasting my time.


From contributor D:
If you can't sand out the streaks and cover 'em up with a fresh coat, then try (if you've got the same finish) a coat of higher sheen, gloss or semi, then lay some 35 sheen on top and see what happens. By this time, you've got two more coats you should be able to rub out and get what you want.


From Paul Snyder, forum technical advisor:
If the finish is flat and level, and there aren't any micro-bubbles, then what accounts for the variations in the sheen?

I'd also try sanding back and re-spraying first. I'd level sand with a random orbit and 220 and then shoot another coat to see how it looks. If the sheen is still striped, the only thing that makes sense to me is micro-bubbles.



From contributor G:
I've seen this. We called it "tiger striping" and it's from incorrect gun settings - the ends of the fan put more on than the middle, and it's usually in the seal coat. If you can sand well enough to get them out without cutting through, you may get away without redoing them. On the other hand - if they don't sand out, you'll have wasted the time you could have used to sand back to the wood and refinish.

From contributor D:
We had this problem before and it was due to too much air pressure. It was also with a new gun. The streaks flowed out and had correct sheen, but the in-betweens dried too fast to flow. We really tweaked it all till we figured it out. On a big tabletop, it was a bad scene, but it did buff out.


From contributor N:
Actually, it's not a tip issue, it's a pressure issue. You should always spray a gun pattern on a piece of cardboard before you start a project. In automotive finishing, this is standard practice and it should be in furniture finishing as well. The viscosity of the material will determine how much pressure you need to get to the airhorns of the cap to break up the material uniformly. Too much and you split the fan. Too little and you have bad atomization and the fan is center heavy. The only thing the tip does is control the amount of material laid down per unit of time. You're exactly right about the difference in thickness throughout the fan causing the sheen problem, but you're wrong in blaming the tip. It's the adjustment of the air pressure that's causing the problem, not the tip.


From contributor J:
Too much acid (catalyst) will cause dulling in the thick part of the coat. It sounds like it was just one topcoat. The second topcoat should have hid the streaking. I would sand it way down, without breaking color, of course, and give it a box coat. One coat, just wet, cross grain with about 20% over pass, let flash 5 minutes. Then a 50/50 over pass with the grain. Also consider putting down a coat of sealer after sanding down what you have. All depends on where you're at with mil thickness. It's worked for me.

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