Wet sanding, pits of hell won’t die!

Discussion in 'Finely Finished' started by BorderRadio, Oct 14, 2019.

  1. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    I’m about to screw this sucker together but I can’t get these stragglers out. I hate rattle cans, after this I’m spraying it right.

    Anyways, question: can I leave these clusters of tiny finish pits and still get a decent finish? Should I move to the next grit and hope for the best? I’m asking because I’m starting to burn through around control cavities. I do not want to spray another layer of clear nitro, but I do want a decent job. It’s been sitting for over 3 months before I touched it, and about another month since I put it down for work on other things.

    Thanks.
     
  2. RodeoTex

    RodeoTex Poster Extraordinaire

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    I get those a lot too. Usually I just spray on a ton of clear in the area, then let the sanding get it out. Sometimes yes, sometimes not so much.
     
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  3. bender66

    bender66 Poster Extraordinaire

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    Pics?
     
  4. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    Oh yeah!

    46F44D71-5720-4AC2-B606-224675C23648.jpeg D26F590E-7ABF-4B87-AEF5-905F86148041.jpeg
     
  5. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    It’s all reranch, with some watco clear on the last few coats.
     
  6. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Why? The lacquer you used dries in 30-60 minutes. There is no "cure" time - you could have wet sanded the next day.

    Except it looks simply like the clear coats did not flow together fully. The mil thickness is, IMO, too light. It has nothing to do with aerosols vs spray equipment, it has to do with knowing when you had enough material applied and recognizing when it was melting/flowing together.

    There are quite a few question as we don't have sufficient information yet to determine what's going on.

    1. What were the temperature and humidity during application?

    2. Were you shooting with the body suspended vertically or laying flat?

    3. How was each coat applied? Were there any differences between the color coat and clear coat application methods?

    4. What sanding sealer was used, and what body wood is it? If the b ody is an open grain wood, what grain filler was used and how as it applied?

    5. Did you use a sandable lacquer primer between the sealer and color coats?

    6. How many coats of color did it take before you had full hide?

    7. Full-surface wet sanding is generally a repair operation used when there are inconsistencies in application - not a normal part of opaque coating applications (it's used on some very thin film, precision lacquer applications - like Gibson's Sunburst Les Paul finishes). Generally thins type of coating system should be able to go straight from final clear coat to buffing, and within day or so with conventional lacquers (not slow dry lacquer enamels like Colortone or Deft).

    8. How much practice spraying did you do on scrap of the entire system, from prep to buffing? That's really key, as with enough test spraying of the specific system a problem like this would have been eliminated before work on the actual guitar started. The issue looks to me like insufficient build (and consequently, film flow) of the clear coating. Additional light application of clear just to the point of even, smooth flow is what I would anticipate - but not until I knew the answers the questions listed. you may have outgassing causing small air or gas pockets that get worse as you sand; you may have solvent entrapment for any of several reasons; you may have an unsufficiently sealed and/or filled wood grain - those are things that will likely be answered through those questions.

    Good luck!
     
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  7. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    You mean people aren't psychic and can read my mind? :D Thanks for your reply.

    This is reranch lacquer, and I've had good results before. Watco too, not an issue, but 30 to 60 minutes? I'm under the impression I have to wait 30 days before I wet sand and buff.

    1. Shot over the spring and summer in the Sonoran desert. I did not shoot in anything over 100 degrees, and avoided the 90s whenever I could. We had a crappy rainy season, but still never shot in humidity over 33 percent or so. It was typically bone dry, less than 10 percent. Unfortunately, I tried to stay on schedule time wise but there were some stretches in between when no painting was done. Each time I started again, I cleaned up the body, tacked it down, using a mist coat first, the sprayed 2 heavier coats, keeping pace with the way the paint was laying down that day.

    2. I suspended the body and neck.

    3. Standard Reranch protocols here, on alder. RR sanding sealer, leveled with my favorite acrylic sanding blocks I bought at the auto paint store. RR primer, RR surf green color, then clear, using RR first then finishing off with Watco. I'm leveling with the said block.

    4. See #3

    5. Sure did, why wouldn't I?

    6. I don't remember. I bought two cans, used them both to avoid sputter at the end of the can life. Pretty descent coverage, pretty thick color coat. Clear coats, probably about 4 cans, including the neck, and again, avoiding the end of the can, though I didn't care that much on clear since I planned on wet sanding any orange peel and other garbage that settles while it's out-gassing.

    7. Hence my desire for a decent spraying system. Try spraying cans in desert heat, outside, at a dusty reservation house. It's sub-optimal to say the least. I can tell when it's going to be bad, the nozzle just not flowing enough, covering enough area, evenly enough because there is a slight breeze. My spray booth was a frame I built with a rotating hanger, easy to move around. I laid down some clear tarp on the sides of the booth to provide a wind break, but the breeze direction can't be predicted.

    8. Not my first rodeo. The sub-optimal conditions made this build a PITA, and I just want some advice how to continue to avoid throwing it in the fire wood pile. Everything else is great, but I have these little patches of small pits that might be deeper than the rest of the finish--seems like I should just nuke it with clear and wait another month. It's cooler now, the sweat in my eyes factor won't be such an issue :)
     
  8. eallen

    eallen Tele-Afflicted

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    Something is amis if you are getting these regularly. It is often the result of solvent entrapment. In other words, the previous layer is still gassing off when the next layer goes on trapping the solvent underneath before it can evaporate. When you wet sand you open the pockets where the solvent was trapped. How heavy are the coats you are putting on?

    Another time I see it happen is when the finish is put out in the sun or under heat in attempt to dry it quicker. The heat causes the outer surface to harden before the inner finnish again gets a chance to allow the solvent to evaporate out of it.

    Eric
     
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  9. failsafe306

    failsafe306 TDPRI Member

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    Looks like you may have had some contamination of the wood before you sprayed. I always wipe down with acetone or naphtha before spraying the first coat. Also I’ll wipe the surface with a tack cloth just before each coat.
     
  10. dkmw

    dkmw Friend of Leo's

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    Eric’s got it, it’s likely just trapped microbubbles. If it were me, I’d just live with it.

    In your desert conditions, it could be that the lacquer is prone to skinning off very quickly and trapping solvents trying to gas off. If you spray super heavy coats, you can get this in any conditions. Don’t ask me how I know :lol:

    Since you know what you’re doing and didn’t spray too heavy, it’s gotta be your weather...

    In the unlikely event that those holes go all the way to wood, it’s a different problem caused by gassing from the substrate. But I doubt that’s what happened here.
     
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  11. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    Thanks, makes sense to me. I can get a great 'flow' on one coat, 3 hours later I'm struggling between the narrow nozzle coverage and the quick 'skinning off' on the next coat. Now that I think about it, the challenging breeze conditions makes me adjust my distance on the fly, so some clear coats did come on a little strong. I tried to shoot 3 coats a day, and the temp will swing from "i'm barely sweating, cool" to "Can i go inside now?" :) This is why I think I need a wide and more even spray pattern and ability to tweak the paint mix.

    I'm think I might have to live and learn with this one, I really want to get it done for a friend, but I'll see if they can live with it.

    Which is part of my question: how will this look after buffing the rest of it out? I have a feeling it won't be too bad, and only noticeable on oblique reflections. My spidey senses tell me I've sanded back to a "thin skin" finish, and I can't tell if I'm in the color coat yet. The water bowl still pools white, no color tint yet, but it is a light color to begin with. The burn through was at the edge of the control route, and was my fault: the long sanding block should be half size and I should work around those areas with more care.
     
  12. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

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    Thanks for the suggestions guys. I hear ya eallen, some clear coats did come on strong, probably as I tried to compensate for the spraying conditions.

    I left it outside for about an hour or so after finishing 3 coats, in the shade at all times. The sun kills everything here without access to shade. I brought it in when the smell subsided and hung it in a clean closet. I'm also religious about the handling. I clean with naptha at the beginning of every stage, except between coat sessions, where I use both a tack cloth (lightly) and compressed air. Note the color coat went on great, no issues.
     
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  13. dkmw

    dkmw Friend of Leo's

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    If your friend was expecting a perfect finish, well, it’s not quite perfect.

    If you were going for a slightly worn-in look, a few pin bubbles don’t make any difference at all.
     
  14. eallen

    eallen Tele-Afflicted

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    If I used a spray rig in those temps I would use a slow thinner or retarder to slow the top layer hardening too fast.

    Flaws are the key to learning if we keep at it! Love how you are making the best of your weather situation!

    Eric
     
  15. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    A common misconception. Absolutely not necessary unless you use 1) a lacquer enamel that's very slow to dry, like Deft or Colortone (if you see naphtha on the MSDS it's a fairly sure indicator it's a s-l-o-w dry product) - conventional lacquers dry only by evaporation, and DO NOT "cure" Every local finisher I know buffs the day after final clear coat application; or, 2) one or more coats are too thick (see below)

    For future reference, "hard rubber" sanding blocks are much better - and safer for the finish - than hard blocks, which can gouge and sand at uneven levels. Rubber blocks spread the pressure over the surface, creating more consistency. A few pros use hard wood or acrylic blocks, but they take pinpoint control over pressure and are relatively useless on curves and edges.

    Just asking - some don't and omitting it can cause the coatings to sink into the substrate.

    This , I think, is your problem - as do others, apparently.

    Thick coats cause solvent entrapment, impair the drying process, can cause "color float" (where pigment separates from the binder), discoloration, delamination and peeling.

    A single coat of lacquer should NOT cover! As I used to say in lacquer application training classes - "It ain't paint!". If a color coat covers fully I can pretty much guarantee - no matter WHAT color - it's too thick. Coverage and flow occurs at 2-3 coats thickness in most cases if it's properly applied, which is why - especially with aerosols - it's recommended to apply each coat THINLY and transparent in 3 VERY thin, even passes.

    Once you have coverage and somewhat even (but not necessarily smooth) flow-out your color application is done. Even your first couple of clear coats are best applieed the same way.

    Lacquer coats melt into each other and smooth, even application "appears" as you SLOWLY build up the film. The last 1 or two clear coats can be applied as flow coats - IF you have practiced enough to make them smooth and even.

    It's absolutely impossible to measure material thickness by number of cans used, as "cans used" depends on spray technique, distance from surface and environmental conditions.

    But FOUR coats of clear? I can't think of any conditions where that would not result in a poured-on appearance *IF* applied correctly. That should be plenty for the body, neck, and all the practice spraying you should need ("practice spraying" consisting of prep. seal, stain/dye/filler or priming, color coats, clear coats and buffing until you can do it all without problems.

    Agreed. Coating over an improperly sealed surface often appears very similar to overly thick coating with solvent entrapment in some areas and outgassing - bubbles - in others.

    In my opinion the individual coats are being applied at full coverage like enamel spray paint, FAR too thick for most applicators to do successfully under even ideal conditions.

    You CAN'T apply a coat of any lacquer too thinly because of it's inherent self healing/self leveling abilities. But application of even ONE coat that is too thick can foul an entire project.

    The two things I can't stress enough:

    1. Perform COMPLETE preparation and practice application on scrap until you have things down to a science and are close to being able to help beginners solve problems.

    2. Think THIN. It ain't paint.

     
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