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Finish Sand Threw...
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=46563		 Page 1 of 1
Author:  sdsollod [ Tue Oct 27, 2015 5:54 pm ]
Post subject:  Finish Sand Threw...
Despite my best efforts I sanded threw my EM 6000 finish on the edge of the back. I was wet sanding (using lemon oil which was working great) with 1000 grit (ANSI) and somehow sanded threw. There should have been enough finish to prevent this, but I guess stuff happens (...especially if your technique needs refining). So, I'm wondering if rather than re-spray the whole back, maybe I should simply "touch up" the sand threw spot. I'm not sure exactly how to go about that and maybe It would be easier to shoot the whole back. How would you go about this? How many coats would be enough, four?

[Dang it. Now I'll have to wait for it to cure again... gaah ]

BTW - I am also finishing another guitar and its coming out great...
Author:  johnparchem [ Tue Oct 27, 2015 6:04 pm ]
Post subject:  Re: Finish Sand Threw...
I have touched up EM6000 on the back of an instrument. It is hit or miss on the sand through. For example if you used zpoxy or shellac to seal or pore file it is hard to match the color and the sand through shows up. Anytime I have tried to fix the color I always ended up with a ring right at the boundary between the sand through and the finished area.
Author:  J De Rocher [ Tue Oct 27, 2015 8:27 pm ]
Post subject:  Re: Finish Sand Threw...
I've sanded through EM6000 close to the edge of the face of an ebony headplate and at the edge of the backside of a mahogany headstock. Sucks. Fortunately, on the mahogany I didn't sand through the underlying sealer coats so color matching wasn't a problem.

In both cases, I applied EM6000 (no retarder) to the sand through area using a very small water color brush. The area of the first coat extended outside the sand through area overlapping ~1/4" onto the surrounding finish. Each subsequent coat extended out a smaller distance so the area of each successive coat was a bit smaller. My theory was this would help with feathering the new finish into the old which it seemed to do. Three coats, four hours apart and then three more coats four hours apart the next day. I let it cure about a week and then carefully sanded and polished using the sequence I would for the original finish. The sand through I was most worried about was the ebony headplate, but the repair came out completely invisible. There's nothing special about the number of coats I used. That's just what I tried and it worked for me. I don't know if this approach would fit your case, but something to consider.

Do you think the sand through happened just from over sanding or might that spot be slightly high?
Author:  Mike OMelia [ Tue Oct 27, 2015 8:37 pm ]
Post subject:  Re: Finish Sand Threw...
If u are an OCD perfectionist like me, u will accept the technique failure. Sand (at the very least) the back back to epoxy etc. Add an epoxy wash coat if you sand through for color evenness, and refinish. The only bummer here is the number of coats required for em6000. Gonna take at least two days start to finish. If you only do the back, tape up the body.
Author:  sdsollod [ Tue Oct 27, 2015 10:36 pm ]
Post subject:  Re: Finish Sand Threw...
Mike, I do tend to be a perfectionist but sanding off the whole back doesn't appeal to me... Jay's solution sounds promising. I don't know if the edge is high or not. Using 1000 grit I didn't expect to sand threw. The area sanded threw is only a couple of mm just beyond the binding. I don't think there will be discoloration...
Author:  J De Rocher [ Tue Oct 27, 2015 10:45 pm ]
Post subject:  Re: Finish Sand Threw...
How large is the area of the sand through?
Author:  Mike OMelia [ Wed Oct 28, 2015 11:04 pm ]
Post subject:  Re: Finish Sand Threw...
Egg shell paint. Wonderful, expensive stuff that looks great and performs even better. But ask any painter how you repair it. You do a whole wall till you meet and edge or corner. Otherwise, you will see the repair. I've done that both ways depending on cost, expedience, and prominence. You will find that no matter how hard you try, it will never look like a sprayed, leveled, and buffed surface. Of course, it's all about cost, expedience, and prominence. That's all I was trying to relay here. Please let us know how it turns out.
Author:  jfmckenna [ Thu Oct 29, 2015 8:33 am ]
Post subject:  Re: Finish Sand Threw...
It's been my experience with EM6 and any water based finish that I have tried that if you sand through you will never be able to get it back right unless like Mike said you sand off the entire plane of the surface and start over. I am by no means a finish expert... In fact I HATE finishing. I'm just sharing my experience with that terrible frustration of sanding through a water base finish.

Good luck!
Author:  J De Rocher [ Thu Oct 29, 2015 12:08 pm ]
Post subject:  Re: Finish Sand Threw...
Given what I wrote above about the repairs I made to sand through being invisible, it's not correct to make a blanket statement that you can never get it right. Not true.

I agree that sanding off and starting over gives better odds of success assuming you don't sand through again. The repairs that I described were on the headstock which, being a flat surface, does make it easier to blend in the repair seamlessly than on a compound curved surface like the back or top.

If Steve can afford the time to try a spot repair, then why not give it a shot? If it works he has saved all the hassle of sanding off the entire back and starting over and he can add a new method to his Luthier's Bag O' Tricks®. If it doesn't give a satisfactory result, he has at least given it a shot and maybe the experience would give him ideas for how to apply that approach with modifications to a different problem in the future.
Author:  Mike OMelia [ Thu Oct 29, 2015 9:21 pm ]
Post subject:  Re: Finish Sand Threw...
I totally agree he should try. But follow the 11th commandment. Thou shalt not fool thy self. If when the attempt is done, and it is not the anticipated result, punt. It's not that big of a deal to sand back and do it again. It would take a day to do. And there is a lot of learning that occurs. My big point is, if u can tell its repaired, it's not repaired. My second point is, it's not horrible to sand back and do it again. I've done this many times. IMHO, once u acknowledge a finish failure, it's best to go back to step one. Saves time in the long run. The good news is EM 6000 is repairable. Witness lines are unlikely. Activate surface with sanding and DNA.
Author:  J De Rocher [ Thu Oct 29, 2015 10:10 pm ]
Post subject:  Re: Finish Sand Threw...
Mike O'Melia wrote:
But follow the 11th commandment. Thou shalt not fool thy self.


Words to live by. [:Y:]

I completely sanded the finish off of a top once and started over just because I didn't like how the sealer coats had darkened the top unevenly based on differences in the bear claw figuring. I accepted that I would never be happy if I didn't do it over.

Thanks for the tip about using DNA.
Author:  SteveSmith [ Fri Oct 30, 2015 8:22 am ]
Post subject:  Re: Finish Sand Threw...
I've got two guitars in the drying cabinet right now which are on their complete finish. First time I used a water-based finish that just didn't work out. Second time I did a pore fill that just turned out too light (walnut and mahogany bodies). Third time looks to be the charm. I also had the chance to retop one of them because it was just too flabby.

Lot of work? Yep. Basically set me back months on getting these done but I should did learn a lot! James Condino told me once not to be afraid to rip a top off or redo any other part of the instrument if I didn't like it. Good advice.

That said. I've repaired EM6000 and it works well as Mike has said. As long as you can get the color match right (i.e. did you sand through shellac sealer or epoxy fill?) you should be fine. One thing I did find out about EM6000 it that if it is applied to the wood directly (a mahogany neck in my case) without a shellac sealer it will chip easy. Good luck with your repair.
Author:  jfmckenna [ Fri Oct 30, 2015 9:31 am ]
Post subject:  Re: Finish Sand Threw...
It's definitely worth a shot. Like I said I'm no expert and those who are can make a lot of money repairing finishes to where you could never notice it so chalk it up to the famous quote, 'there are no mistakes there are only learning opportunities.'
Author:  Mike OMelia [ Fri Oct 30, 2015 2:59 pm ]
Post subject:  Re: Finish Sand Threw...
Btw, if u sanded to wood, would that lemon oil pose a problem?
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