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I'm finishing a guitar with Watco rattle can Lacquer, which i do believe is nitro based. Some spots i measured had about .005" in thickness applied before sanding. After sanding it is down to .003" or so. It is wet sanded to 600grit, which gives it an even satin look. I'm satisfied and will leave it at that, unless you guys convince me otherwise.

So my question is: At that thickness, is a nitro finish still susceptible to crazing?

This was a fairly easy finish to apply, and will gladly use again on more instruments. I'm planning to go to high gloss with the next one, but will not do so if this finish will craze.

edit: Neglected to ask about a nitro finished neck? I've been using a try-oil finish on my necks, which i'm happy with. Or do you suggest a nitro finish instead?

most crazing happens from thermal shock. Your finish is thin so you should be good. Also how find did you sand ? I don't like to sand much past 180 220 grit. Too fine you can find adhesion problems. I also prefer to use the vinyl sealers or what is recommended by the manufacturer. Also Deft always seemed to give me a problem and I only used that on my first guitars.

I sanded with 220 grit I believe. What I did for pore filling is I applied the Watco brush wipe on nitro onto the bare wood. I than scraped and sanded back. This gave me an even surface for the rattle can application.

Am presuming I'm fine with the above. Easy enough. Or am I inviting issues?

you should be ok

Deft is a weird product. I recommend staying completely away from it. It crazes, never hardens, reacts badly with some case linings, and imprints if the instrument is left leaning against, or laying on a variety of materials. Everytime I say this, I get people who say they finished their instrument 50 years ago with Deft and it is still beautiful! I don't know the answer to that one. It's just a hit and miss thing.I do know that I have seen dozens of sad cases over the past 40+ years that I have been building, repairing, and teaching. I suppose it is because Deft is one of the few available rattle can finishes and it is called lacquer. Unfortunately, the word "lacquer" is meaning less when it comes to identifying what a product actually is. Once you have started a finish with Deft, you definitely don't want to do any overcoats with any instrument lacquer. The chemical reaction between the 2 is general devastating.

Thickness measuring at the bridge area (I had taped off) shows I have a thickness of .03 inch. So I'm presuming this will not craze. I'm hoping this is a reasonably durable finish.

never can you say it won't craze but if you keep the thing from thermal shock you should be fine
I think .003 may be thin. I agree a thin finish can be ok but remember a finish is there to protect the wood. I once had the idea that the super thin finish would make a great guitar but there is a thin line from protection and crud. Oils from the skin get into the wood and it can really be a tone killer.

3 mils is pushing the low side limit of film builds for air dry lacquer. Checking induced by wood movement can be a problem with low film builds as there is not enough material to expand properly in times of higher RH. Resistance to wear will also be diminished. Best practice is to target a film build of 5-7 mills final thickness after all leveling and buffing.