Official Luthiers Forum!

Can anyone advise on what’s happening? I sprayed black on this bass body. I didn’t do anything different than I normally do. After wet sanding I use three buffing wheels - medium, fine & ultra fine. Normally it looks like a sheet of glass when I’m done. This time, I’m getting these marks. They go in the direction of the buffer so I know they’re not sanding scratches. Admittedly, I haven’t done that many solid black finishes and I know that black is more revealing but this seems like something is wrong. I’ve tried raking out my wheels and cleaning up any stray fibers in the wheels but to no avail. Anyone have some insight into how I can correct this so I can give the customer back his instrument?

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

In my experience black is the hardest to get looking nice after buffing. When I worked for a small guitar company we would finish with a liquid polishing compound by Meguiars on the buffer for black finished. You may need the next grit up from whatever you are polishing with.

First of all, what did you shoot on this body? Nitro? Some kind of poly? And how long did you let it outgas before beginning to buff?

_________________
"Act your age, not your shoe size" - Prince

Nitro. Schedule was -

Prep - Vinyl Sealer - Level - More Vinyl Sealer - Color - A couple tack coats (It sat for a a couple weeks at this point due to weather/schedule) - 6 or 7 Coats of slightly thinned clear. I used Mohawk Classic Instrument Lacquer. Wet sanded & buffed after 10 days cure time. I know there are differing opinions on this. The manufacturer claims 3-5 days, I believe. I’ve heard people say they wait as long as 6 months which seems extreme.

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

You could try hand buffing with a lighter touch using an automotive finishing glaze. I usually do a "soft buff" after a couple of weeks, but thinK it takes a month to bring it to a hard shine. The finishing glaze may help you minimize the scratch marks . Cheap microfiber cloths or worn out cotton T shirts are good for hand buffing.

Hmm.... a month? That’s what I’m starting to wonder about. Is it probable that the lacquer is still too soft to stand up to the buffing wheel? It would make sense, in theory. I called StewMac and asked them if this could be a sign that maybe my buffs are wearing out. They could have easily talked me into purchasing more but the guy I spoke to seemed to think they were fine. He said rake ‘em to get any crusty stuff off and maybe check between the flaps for renegade particles. I did all that and they seemed as clean and soft as the day I got them. I also tried using a cloth (100% cotton T) and Novus#2 but that wasn’t any better. I haven’t tried microfiber yet but I may go pick some up and give it a shot.

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

I use to get those marks with cotton wheels and dry wax compounds. Since I switched to automotive wet compounds and foam pads, no more problems.

Check out my posts near the bottom of the first page in this discussion for more details:

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=52716&hilit=adams+swirl

Finishing glaze has little or no abrasive and just kind of smooths over small scratches. It's not a permanent fix, but then having a perfectly shiny black lacquer finish on a guitar that gets played isn't permanent either. Finishing glaze is more of a "get it out the door" or "day of the car show" thing.
In the car show rooms (before the days of clear coat) they used to wipe the cars down with Windex to bring out that "show room shine". The first time it rained after the car was driven off the lot the "show room shine" disappeared.

I would suggest a longer cure time. 3 weeks at 70 degrees minimum. Black is a challenge and automotive compounds can be your friend. I apply them by hand. Good luck!

Thanks to everyone for the info. I feel better knowing that I’m not the only one that has encountered this. I think I’ve seen bonnets (maybe wool?) that slip over your random orbital sander for polishing. Does that sound like a good idea? I also have a set of foam pads that I bought from StewMac a few years back. I stopped using them when I got a buffing wheel setup.

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Most random orbital sander's spin slows down to where they don't polish very well. Barry Daniels had a suggestion on a recent thread about direct drive RO sanders that work better...https://adamspolishes.com/collections/e ... g-machines. I used a HF 3" air polisher recently that worked a lot better than the Bosch RO for getting a shine.

I don't buff lacquer for at least 4 weeks. No matter what the manufacturer says.....

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Ask your client if he wants it good, or fast..... Pick one, because you can't have both.

_________________
"Act your age, not your shoe size" - Prince

I picked up an orbital buffer for $35 at Home Depot and some Maguair’s polishing compound. The results were surprising. I now realize that I don’t have much experience with solid black finishes. I see what others mean when they say black is a very revealing color. This just confirmed that my wet-sanding was more than acceptable. Now if I can just figure out a way to give it back to the client without messing it up.

_________________
"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."