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I will definitely be using retarder next time. The humidity was changing as I sprayed the different coats, which is why there are some areas with blush and some with less.

You’re right, it is thick. It’s about 0.012". The whole time I kept thinking I was gonna burn through, but when I was finished, I measured the tape that I used to mask off the bridge to ascertain the actual thickness. I thought that maybe it would sound a little less than perfect, but have extra protection. I was wrong. It sounds great, but cracked quickly. I just bought a DeFelsko ultrasound thickness measuring tool so I can measure exactly on the next finish.

After reading the thread here on UV finishes, I am seriously debating going that route. I found working with lacquer is less than perfect due to having to wait so long to buff. The fragility compared to other finishes is another downside. I also didn’t care for how long pore filling took.

I’m thinking it’s possible that with my new thickness measuring gauge and a UV cured finish that I could complete the finish from start to end in a day or two and keep it very thin.

A quick FYI, the only thickness gauge that works on wood that I know of is the Defelkso Positector 200. It is quite expensive at around $2k. Other gauges work great on other substrates like metal but will not give you accurate measurements on a guitar finish.

I don’t doubt that thickness gauge is a great tool but Defelkso Positector 200 sure sounds like something a scientist played by Rick Moranis would have invented in an 80s Mel Brooks film


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Simon, I was considering the magic probe that SM is carrying and doing an A to B measurement before and after finishing. The unit measures in mils but I cannot find any documentation on the SM or the product website stating if the resolution is +/- .001 or if it is simply showing readings in mils. If it is high enough resolution it seems reasonable that you could measure a very specific area like the bridge plate before and after finishing? Might be worth it for a few hundred bucks. I sent a mail to the company as well to ask, but have you looked at that product?

Sorry to sidetrack the thread.


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I think you meant sand through. But then again, that's the magic of Nitro. Spray area with an air brush...light sand, buff. I believe one of the largest producers (Martin) still uses nitro. You don't want to get it thick. Nitro gets a bad rap amongst small shop builders due to its flammability. Cost of air supply, explosion proof fan (Jenny, Summit Racing), and so on. These are not to be sniffed at. But they are a one time cost. And once you have invested, life gets easier. WAY easier than dealing with waterborne. Way cheaper than UV. And, most important of all: Repairable. Even yours can be repaired.

EM-Tech 6000 is an exception in the waterborne space. It easy to apply (spray), builds well, water clear, non-toxic (but still mask), non-flammable. Can be tinted. Biggest drawback is the blue cast. And its repairable.

I have a Magic Probe. It reads to 1 mil. In the range of guitar top thicknesses, I subtract 3 mils from my readings to match my caliper measure. If you get one, you will have to do your own calibration for your unit. I haven’t used it to measure finish thickness, but I suppose it could be done. My top thicknesses vary by 2 to 3 mils over a small area, so looking for a finish 3 mils thick would be problematic.

Indeed, that is what I purchased. The DeFelsko Positector 200 B1 to be more precise. I tested it on my stable of guitars. It is very fast. The guitar I just built is the only known thickness and the DeFelsko measured very accurately - matching my Mitutoyu caliper’s measurement exactly. I took a measurement with my caliper by measuring the tape I pulled off of the soundboard that was used to mask off for the bridge. I measured right next to that area with the DeFelsko.

You’re right. My biggest worry with “sanding“ through was that I had already waited six weeks to finish the guitar after I sprayed it. Waiting another six weeks would have been an unwelcome turn of events.

I’m still not sure what material I will choose to finish my next one, but the UV sure is appealing based on the VERY short cure times.

Thanks for the recommendation on the EM tech 6000 I’m going to look into that.

Here’s the UV system I’m looking at. It can be brushed on, rolled on, or sprayed on. I’d probably spray it.

https://www.cureuv.com/collections/uv-guitar-finishing/products/ps-uv-curing-system-guitar-finish-starter-kit

Tom—

You will see many posts from Alan Carruth here on the OLF about there being no perfect finish. I agree with that view. Every option has its own set of upsides and downsides. It sounds like you have already read things I have written here about my experiments with UV cure finishes. You should also look for posts by Brad Combs and Brian Howard. They know a lot more than I do about the UV cure finishes. Weighing the goods and bads, I’ve decided that UV curing is the right way for me to go. Many folks will disagree with that choice, but that’s going to be true no matter what you choose. If you go with UV cure, you might want to watch eBay for used curing lights. I have gotten great deals that way. Another option is catalyzed finishes. Either UV cure or catalyzed gives the best protection. But they are more difficult to repair. And paying attention to personal safety is very important, no matter what you apply. Like I said, there is no perfect finish. Good luck with your decisions.

And I agree that your first guitar turned out great! Yes, you had finish problems, but the woodworking looks well done. It’s a fine start. Congrats on that. My first guitar looks like a 3rd grader built it, compared to yours.

Thanks for the info, Don. I’m excited to give UV a try.

Thanks, Bob. You make a great point about trying to repeatably measure the same small area. I did reach out to the company and here is their response:

The accuracy is around 0.1mm or 0.003". Generally I would say it is not ideal to measure the small differences you are talking about.
There are other factors that play into it like friction, probe angle etc that may mean your 2nd measure isn't at exactly the same angle as the first so you have some offset adding to your film measurement.
Sorry and thanks for your interest.

Apologies for the off topic.


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Op said he did not want to wait 6 weeks for repairs to nitro. I’m not going to deep dive this. Nobody I know would do that. There are ways to get things done if u know what u are doing.

Another way to shorten wait time is to make sure surface prep is as good as it can get. Nuff said.

I posted here asking how long to let nitro cure. The conclusion was 4-6 weeks. Perhaps my logic is flawed, but if I sand through lacquer when sanding the final coat, I would assume I would need to wait another 4 to 6 weeks after re-spraying until I can sand again and buff. Is that wrong?

It was quite a challenge for me to sit there, staring at my first built guitar for six weeks before sanding and buffing, all the while being unable to play it. I was scared if I sanded through I would have to repeat the entire waiting process.

Perhaps I don’t understand the process properly?

Plenty of people wait less than 4 to 6 weeks. Especially repair shops. I hesitate to throw a specific number at you because the environment the finish is curing in, whether you used any slow solvents and if so how much etc all plays in to things.

Tom—

In case you feel you would benefit from some guitar-specific finishing instruction, let me recommend a handful of finishing video courses by Jeff Jewitt, access to which is sold on Robbie O’Brien’s Luthier Academy website. That website has lots of good instruction (for a reasonable fee), but for finishing especially, I think the Jeff Jewitt videos are excellent. There are at least four courses I can recommend: spraying nitro, spraying catalyzed urethane, spraying sunbursts, and sanding/buffing. If you want to go the UV cure route, the catalyzed urethane and sanding/buffing courses are the most relevant, and I would recommend looking up a blog post by Brian Howard about how to work with UV cure finishes, and meshing that info with what Jeff Jewitt teaches. Between Brian Howard, Jeff Jewitt, and some of the info here on the OLF, you can get a good start for your own experiments. Good luck.

For "sand throughs" waiting a couple of days before leveling, and a couple more before buffing can work. Giving them a week to dry would be better. Sand throughs are usually small areas that are given a couple of coats and then leveled and buffed by hand.
For many of us (amateurs) waiting 4 to 6 weeks before finishing the finish is not a penalty. We already have the next one on the bench and no pressure to get the last one out the door.

I have a few of his courses. He says to wait six weeks. That’s why I came here to ask, because I didn’t wanna wait that long haha.

Thanks for the tip on the Jeff Jewitt course. I've been eyeballing a few of his courses.

A trick to speed up lacquer curing is to lightly sand the surface before the wait period. The sanding exposes a lot more surface area which allows the solvents more pathways for off-gassing. In my estimation this speeds up curing by at least 30%. A light breeze from a fan will also speed up curing.

Another thing that helps is gentle heat.

Thomas T, just read your Devastating end to first build story, quite enjoyed reading about the journey. And the final product was very nice!! I've had a similar journey and can relate totally.

I've built three, and everyone has had a devastating event. The first went the smoothest, so what could go wrong with subsequent ones? Then the first one fell over and broke the headstock almost completely through- sounded like a home run in Wrigley field- very satisfying repair however, including the persistent fisheye on the overlay requiring full removal of the lacquer there and washing with mineral spirits, naptha and ammonia.

Lacquer cracking on the first two. Stripped lacquer off the neck of #2 due to white crap developing in the pores weeks after first lacquer: Water based grain filer issue- root cause still unknown but suspect there was water in the grain from grain raising, that got sealed off with the filler. And I won’t soon forget scraping all the lacquer off the top due to cracking before my eyes (lacquer too thick). Spent 12 months on finish issues alone (including much experimentation on re-flowing the cracked lacquer on the top). Experiments were successful but my hypothesis was false, re-amalgamation of the cracks ( drop fill, thinned lacquer, thickened retarder, blush reducer ect.) was not successful.

No lacquer crack on third but it fell off the bench in an unexplained and quite ghostly overnight event- cracked the top and shattered the lacquer. Took 8 months to repair and refinish, the crack, starting from the edge of the lower bout, would not close so I added my first splint, and did not nail the color. That one is-what-it-is, and structurally sound.

I'm on my fourth, the first scratch build (first three were wood-in-box kits). So far nothing devastating. Maybe because I drag my feet completing carving the neck. The chisel path and order of cuts of the dart volute has me perplexed. At the worst, I can carve off the volute. I just can't seem to throw in the towel on the arrow volute.

I can relate to your agonies and the final thrill of victory. Guitar building for me is akin to moths to flame. Looking forward to reading about your subsequent builds.

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