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PostPosted: Sat Dec 22, 2007 4:20 am 
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I've completed the first five coats, which went on pretty well, and today I'm gap filling, level sanding, and applying the final five coats, per Mike Doolin's schedule.


My question is, in level sanding, is the objective to simply knock down the barnacles, or to thoroughly smooth out the surface free of any orange peel?


Thanks in advance.


Ken


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PostPosted: Sat Dec 22, 2007 5:36 am 
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Perhaps I'll just go for a happy medium, levelling the surface somewhat, but stopping well short of possibly sanding through yesterday's coats. Logical?

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PostPosted: Wed Dec 26, 2007 2:38 am 
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Old Growth Brazilian
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You want the film smooth everywhere. No orange peel or low spots left.

If this is your first time to level out a sprayed finish, you can expect to sand through in a couple or more places. As soon as you see the sand through happen, stop sanding in that area and move on to an other. Get the film level everywhere else. Once you have the film leveled spray 2-3 more coats. Allow to cure and rub out again. If you have no more sand-through, then polish sand to 800p through 2000p or use micro-mesh 2400 through 12000 and buff out to desired gloss

Unfortunately It has been my experience that it will take spraying and rubbing out several guitars before you get to where you seldom sand through at least a spot or two. It is just kind of the nature of the beast.

It has more to do with your prep and spraying that with the fact that you over sand. to avoid sand through requires that the film be built up reasonable level.

Corners and valleys are the most common areas that you will sand through at. But in any case you want to get the film to be one continuous level plane.


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PostPosted: Wed Dec 26, 2007 2:58 am 
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I guess I should back up and say the first leveling, prior to final finish coats I level as close to smooth as reasonable. My though process here is to aid in building a very close to level final film. If I sand through I had rather it happen ow than after the final coats if possible.


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PostPosted: Wed Dec 26, 2007 4:31 pm 
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Michael --


Thanks for your response. I went ahead and gap filled, levelled (somewhat), and applied the final five coats last Saturday. Since I had family coming in that day, I had to get the finish on, then get cleaned up in time for their arrival. Hours later, while showing off my handiwork to my sister and bro-in-law, I began to notice numerous small circular indentations on the granadillo sides and ebony head plates of both. This phenomenon was definitely not present after the first five coats, and I haven't noticed it on the mahogany back, sides, or necks at all. Here are a couple of examples shot in raking light:




Any idea what might have caused this? I'm hopeful that these will sand/buff out, but if they don't, do I have any recourse? It will be at least ten days before I can begin the final sanding/buffing process.


Also, in the second image you can see the texture on the surface that I have to work with. On my first build, I don't recall the surface being any worse than this, and I was able to get it fairly smooth.


Thanks for any thoughts/feedback.


Ken


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PostPosted: Thu Dec 27, 2007 2:33 am 
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Old Growth Brazilian
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The dents are likely cause by moisture in your air supply. wipe the area with DA allow to flash off and drop fill using a toothpick. allow to cure three days. Take a razor blade and grind the corners round. burnish a hook on the razor blade and use like a scraper and slowly and carfully scrape the drop fill to near level. Allow the finish to cure. The longer you can allow to cure the better.

Your not quite level yet on your film judging by the photos. There is still a good bit of orange peel but it is getting close. That's OK.

Once cured finish out wet sanding with distilled water and a drop or two of dish soap, 400p, 600p, 800p, 1000p, 1200p, 1500p and 2000p or Micromesh 2400 through 12000. Each progression should remove the scratches left from the previous grit.

Once sanded level through 2000p you will have a pretty close to high gloss. Then polishing with a glaze or buffing from medium compound through fine or extra fine will finish up.

Keep in mind the longer the cure the better the film will take the buffing.


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PostPosted: Thu Dec 27, 2007 2:45 am 
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I have had the same thing happen with Target USL and I found that it was as Michael said, moisture in my air line.  Actually, it is moisture and oil from the compressor.  Make sure you drain your tank of moisture and use a water trap so the air is perfectly dry and clean before it hits your spray gun.  Also, as Michael said it looks like you still have some leveling to do as both photo's show quite a bit of orange peel. Typically, my guitars look like that before I start level sanding.  Don't give up, you finish looks good it just needs a bit more work.  On my first 4 guitars I used Micromesh all the way through the 12000 grit level, but on my last ones, I have stopped at 3600 and then used buffing compounds to get the final finish.  It saves a lot of sanding, and also lowers the possibility of rub-through dramatically.  Although Micromesh says you won't remove enough material to rub through after about 3200 grit, I have rubbed through several times after 6000 grit so it is very possible.


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PostPosted: Thu Dec 27, 2007 2:59 am 
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Ken, Those actually look like fisheyes. Fisheyes are caused by contaminants in the air, in the air line, on the surface before applying clear, and also from your own body. Did you use any type of surface prepping solvents prior to applying the clear? This would be a wax and grease remover and is wiped on with a clean towel or rag and wiped off with another that is dry to remove the residue. be careful with paper towels as some of the glues in the consumer paper towels will cause fisheyes.  Sometimes you can dab some clear into the (crater) fisheye and level it when you level sand later and get an acceptable result. Wax, grease, oil, some deodorants, and even your own body oils can cause fisheyes.


The craters could also be solvent pops which can be caused from applying too much material too quickly and trapping solvents that later make their way back through the layers of clear. Best way to avoid these is to allow good flash times between coats of clear.



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PostPosted: Thu Dec 27, 2007 3:03 am 
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Many thanks, Michael and David for your excellent advice. That makes sense that the indentations are from moisture, though I do have a trap on my compressor. Here's a dumb question: would water do that even though it's a waterborne finish? Or perhaps it is oil as David suggested?


I'll try the drop fill method on the deeper dents. Many of them are so shallow, I don't think they're any deeper than the texture I'll be smoothing anyway, so I'm hopeful they'll sand out.


Should I worry about adhesion of the dropped-in finish to the existing, five-day-cured finish? Or will the DA still cause them to fuse?


Ken


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PostPosted: Thu Dec 27, 2007 3:10 am 
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Thanks Joe. I was wondering if this was the fisheye effect I'd read about, and so hoped to avoid... I'm wondering if the DA itself could've caused this. I sprayed the surface after levelling the first five coats, and I thought I allowed sufficient time for it to flash off. Anyone ever experience this?


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PostPosted: Thu Dec 27, 2007 3:24 am 
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Yes It will. The moisture generated in the compressed air flow is not pure. it will contain oil and other residue. Joe is right it is fish eye i am not sure he caught on to the fact we were talking about a waterborne hers so the solvent is H2O. The most common introduction to your finish will be through the air supply. But he is right it could be the booth environment, anything suspended in the path of the spray or left on the surface of the wood can cause this. Nothing changes about what I said to remedy the issue.

I am assuming you are using a hp gun or a HVLP conversion gun. Water traps sold in most hardware stores will not eliminate 100% of the condensation in the line. If you are using a hp gun you really need a dryer as well and they are expensive.

If you plan on continuing to spray finishes I would wholeheartedly suggest investing in a 3 or 4 stage turbine driven HVLP system. They will really save you in the long run you can get a pretty descent 3 stage system with a good gun for around $450 even less if you shop around. worth every penny.


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PostPosted: Thu Dec 27, 2007 3:31 am 
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Yes DA our any contaminate can cause this. Notice I said wipe not spray DA. I find wiping will remove most all contaminates that may have gotten on the finish and leaves behind a lighter loading and will flash quicker.

I personally still believe the issue was moisture in the line. It is the most common cause. Are you using a hose set dedicated solely to spraying. If mot you really should. An old hoses that have been previously use with out a scrubber, water trap and oil trap will have all sorts of gunk in the line that can get to your gun.


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PostPosted: Thu Dec 27, 2007 3:54 am 
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Oh I forgot! You should have no problems with adhesion on the drop fill after a DA wipe down and flash off. You must be sure the area is clean and dust free. I would fill the shallow ones as well. a small drop goes a long way. Avoid over filling. practise the technique first.


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PostPosted: Thu Dec 27, 2007 4:53 am 
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Michael --


Thank you, thank you, thank you on all points! I don't know what I'd do without the generous insights you and so many others provide on this forum. I hope that someday I can contribute not just questions, but answers to the other newbie members here.


Again, I truly appreciate your taking the time to offer up meaningful advice. If you ever find yourself in Asheville, NC, please let me buy you a beer.


Ken


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PostPosted: Thu Dec 27, 2007 5:04 am 
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There is a small town southeast right outside of Asheville with this beautiful park built maybe a 1 acre pond with a circular drive that all the streets in town intersect. Just down the mountain about a 1/2 mile to the south is a small cafe setting right along side a decent sized mountain stream That serves the best chicken fried steak I have ever had. and the view is splendid as well.

Diane and I found this place back when we lived in Jacksonville


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