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Wet Sanding/cracked Lacquer


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I was wetsanding my recent build with micromesh and I noticed the lacquer starting to crack around the tailpiece holes and the control holes. So I stopped and waited, the cracks got longer and longer, and finally stopped after an hour or so. I must have got some water in the holes, I was being careful beacuase I heard this could happen. This is my 4th time wetsanding a guitar and I was being as careful as I was with the previous 3 which did not crack - oh well, this guitar build has been cursed from the start. Anyway, does anybody have any suggestions on repairing the cracks? It is nitro lacquer, cured for 2 months. I could leave it, but this is my best finish job - I hate to leave it like it is as I was considering trying to sell this guitar. I tried to take a picture, but it looks worse in real:


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I don't have any suggestions for fixing the cracks, however, when i've used micromesh papers they have worked better for me when dry sanding. The papers load worse and the finish didn't shine as easily when wet sanding. This was, however, sanding a tru oil rather than a lacquer finish. I've always wet sanded things in the past, but with micromesh it really seems to work great sanding dry. Maybe trying that in the future could help avoid the cracks. I seem to recall Westhemann dry sanding the control cavity cover on his 'exploder' as well and having superior results.

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I haven't worked with nitro, but I believe one of its attributes is that it melts in. That said, you might be able to drop some nitro on the cracks and remelt the cracked areas. This will mean you have to wait for it to cure though. In the future, use some melted wax and a nail to coat/fill the insides of screw and stud holes before wetsanding.



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Thanks for the replies. I found a tutorial on fixing cracked laquer on frets.com. Basically, as thegarehanman stated - drop fill the cracks - wait for the lacquer to cure - scrape level with a razor blade - sand and buff. Like I said, this guitar has been a curse (lessons learned):

1- When I shot the burst, a big drop of colored lacquer spit out of the air hole in the top of the gun and landed right in the middle of the guitar (this taught me to put a paper towel over the lacquer cup, secured by and elastic, to catch the lacquer that spit out of the airhole from back pressure). I had to sand the top off, re-dye, seal, shoot the burst again.

2- Then when I was buffing using a sponge pad on my drill, I pushed a little too hard when buffing the neck and the pad fetched up throwing the drill which hit the horn and took a big lacquer chip out, I had to drop fill that and fix it (this taught me to hold the drill tighter).

3- Then when I buffed the top I noticed big sanding scratches in it here and there where I must have not spent enough time with successive grits, I had to start over and go through all 9 grits of micromesh again (this taught me to make sure I spend enough time with each grit).

4- Then the lacquer started cracking around the bridge pin holes and control pot holes, which is the topic of this thread (and this taught me to be very careful with the water when wetsanding around holes).

Good lessons to learn as each mistake adds about another 1-2 weeks waiting for lacquer to cure.

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  • 2 weeks later...

I tried the method above and it worked fine. Under close inspection with a bright light, you can still see a hint of the cracks (because the lacquer did not seep all the way down into the crack - this could have been remedied by first widening the cracks with a knife) - but it is good enough that it will never be noticed by anyone but me - and that is only because I know they arew there.

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I'm glad you found a fix already. Had I posted in time, I would have recommended this fix:

1. Let the guitar dry for a few days, ...let all of the water wick out and the wood dry thoroughly before proceeding.

2. Take a Q-tip swab, dip it in lacquer, and coat ALL existing holes, cavities, or ANYTHING that remotely resembles bare wood, I do this 2-3 times to all holes, lips, and edges that need it.

3. Buy some pipettes and get yourself some laquer retarder.

You 'can' do this with regular laquer thinner, but it doesn't work -nearly- as good as real retarder.

Suck some retarder into your pipette (just a -tiny- bit), and apply the retarder to the cracks ONLY.

Do not let the retarder dribble onto the finish.

Pipettes typically have very very small openings to allow you to do detail work like this.

When you do it right, the retarder will wick directly into the cracks themselves, and not sit on top of the finish.

The retarder will basically melt the halves of the lacquer 'canyons' together again and seal it back up.

Thinner typically dries too fast to allow a good rebonding to occur, why I recommend retarder, the proper choice.

This saves you from doing lacquer drop fills which have to be resanded, and stops the problem of a too-thick drop-fill not thoroughly getting all the way into the crack to seal it back up properly, which they rarely do.

This is the proper way to deal with moisture cracks, not drop-filling them.

Drop-filling a moisture crack is like using a hammer to drive a thumbtack.

It calls for strategic pinpoint accuracy bombing, not carpet bombing :D

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I had a similar experience cracking my lacquer finish when I was an idiot about my bridge installation.

To add to Drak's comment about using pipettes to deliver small amounts of liquid... you can also use pins or razor blades if you're careful. You won't be able to deliver much fluid at a time, but small drops of thinner or retarder will stick to the tip of pins or nails so you can more easily place them very precisely.

It's slow work, but I hope you won't need to do much volume, and then you won't need to find more specialized equipment (or suck up any more fumes for that matter).

- Dave

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Blush remover -is- basically lacquer retarder in a can with an aerosol propellant.

...But is the wrong application process (see carpet bombing comment above) :D

The last thing in the world you want to do with water cracks is to spray blush eraser onto it, you can easily and quickly multiply your original problems that way. :D

Wicking it directly into the cracks without getting ANY on the top surface is what you're shooting for.

Add a drop or two of lacquer to your retarder, use a pipette or a glue syringe, go -very- slowly and carefully when wicking it in, and you get a quick and painless patch with no additional problems.

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Drak, thanks for the information - I will try your method if I ever run into this again, but hopefully I won't.

I wasn't using anymore water than usual and I was doing my best to keep it out of the holes. I think the problem was that this guitar had already been sanded and buffed once, and I had already cleaned up all of the holes of overspray and rounded the lacquer down around the holes to avoid chipping. But I wasn't happy with the top (a few deep scratches here and there) so I started over again with the 2400 micromesh working my way up again, but now the guitar was smooth and the edges of all of the holes rounded over so I think the water tended to seep into the holes easier.

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Just looking at your pics above reminded me of something additional, and that is that if you can trace the origin of the cracks (in your case the very edge of the pot holes) ...that is where you want to direct your pipette or syringe, once you place the tip of your syringe or pipette right there at the edge of the pot hole and depress a bit, the solution will wick itself right in and along the entire crack without you having to try and aim it in from the top and possibly getting a drip onto the top which could be ruinous for a burst job.

If you don't go sloooow, you will wick the crack full and then get a drip of overflow popping out of the crack, which can be a disaster when you were -just- on the brink of complete and easy success.

That split second of patience can mean the difference between total come-back success.......and making things worse than they were to start off with.... :D

Sometimes patience is -everything-.

Personally, I don't think you did anything ~wrong~, this stuff just happens when you use water to wetsand if you don't fill all your edges and holes really thoroughly, it's just part of the learning process.

It's not a curse, it's called a learning curve, and is perfectly normal. :D

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