[abadcliche]

Hey all,

Any tips for preventing lacquer crackling/crazing at the site of dentwork? Especially something like a sharp ping dent in an otherwise perfect bow on a vintage horn with cellulose lacquer.

I've heard of the rick whereby you prevent lacquer crackling/crazing at the site of dentwork by spraying a light coat of clear lacquer over the spot to "soften" the lacquer underneath before pushing the dent out, but my first couple tries on a junker I must not have done it right because it didn't really seem do much.

 

[Thomas]

how about warming up the lacquer to soften it in the area before pushing the dent, say with a heat gun or hairdryer....

 

[Dr G]

I think shooting an overlayer is a good way to go. Consider thinning it a bit and letting it sit long enough to diffuse into the old finish.

Might even try just misting the area with solvent.

 

[abadcliche]

Dr. G, that is kind of the effect that spraying lacquer on it has- the thinner in the lacquer is supposed to soften the old lacquer allowing you a precious few minutes to push the dent out without crackling the lacquer. But like I said, I have not had excellent results so far, and I'm hoping for pointers so I can graduate from junker horns to otherwise flawless collectibles (yikes).

 

[Dr G]

Understood.

Have you tried thinning the lacquer? The higher the solvent content, the more effective.

I used to work with "old" guitars (electric and acoustic) when I was (much) younger. Nitro was the finish of choice for those too.

 

[abadcliche]

Nope, the lacquer I've got is lacquer-in-a-can, no thinning allowed. But this stuff is supposed to work, so I'm wondering if its my technique.

Stewmac does sell a nitrocellulose thinner, guess I could put that in a spray can and give it a go. Scary stuff to be spraying on a horn!

 

[Dr G]

Ah, I see.

I'm used to working with an airbrush.

 

[Henry D]

I did essentially the same thing on old trumpets with crazed lacquer where I pushed out minor dings in the bell/spout/bow area.

I used to use a few thicknesses of old T-shirt soaked in acetone and just gently drape it over the area for "a while" (loosely defined as an thirty minutes to an hour and a half depending on my assessment of how old the finish was and how susceptible it was liable to be to the solvent's effects).

In a couple of cases it worked near perfectly- seemingly melting the lacquer back into a nice unmarred surface. In more cases it did just OK to very little. In some cases it did nothing. In one case it melted the stuff into a gooey mess...

It worked great on an old Selmer Paris K-Modified but not at all on an old Selmer Paris Cornet--- I'd have thought they used the same lacquer so sadly I have no common element to offer- just trial and error.

It stank like hell, as you can well imagine, and I was always afraid that I'd wind up with a massive flash fire in the work-room from all the fumes. I haven't tried it in years- my workroom is contiguous with the rest of the house now and I'd wind up being hung from a tree by my neckstrap were I to use that much acetone where the family got wind of the fumes.

 

[simso]

Matt, I use teflon tape when taking dents out. Sometimes the lacquer will crack but not often.

To flow the finished surface you need to know what type of finish was applied.

If its a two pack poly, then you cannot reflow the surface, you need to remove and respray. If its a single pack then you can apply a rag dampened in thinners to soften the surface which will restore a crazed underbody, if its a cheap style single pack then mix up some shellac and when it dissolves ruib the surface and it will reflow the area

 

[jicaino]

MEK (methyl ethyl Keton). You brush it, take the dent out, brush it again, and pray.

 

[simso]

Mek is not good for you. It is known to dry up the cerebral fluid in your head, for some this may not be an issue

 

[windman53]

Just a suggestion, you might want to try to appliy a layer of nail polisher on it. of course, it only works when dent is small.

 

[slausonm]

Your local auto parts store will likely carry a small spray bottle that you can mix your lacquer and or solvent and spray the horn. They cost ~ $10-15 These bottles are made for spraying automotive paints but work nicely for lacquer if you don't have or want to use a spray gun.

Re dents and crinkled lacquer, IMO you won't be able to avoid it for those really sharp dents, but for shallower dents use the largest ball you can to push the dent up and avoid stretching the metal beyond the minimum needed to get the dent out. The problem with trying to soften the lacquer is that you run the risk of smudging it when removing dents or accidently getting dirt/lint...stuck to it. I would avoid it.
Matt

 

[hakukani]

Mek is not good for you. It is known to dry up the cerebral fluid in your head, for some this may not be an issue

I worked at a motorcycle helmet factory when I was 18. I cleaned my hands with MEK. That explains a lot....