Bar dings: repairable?

Richard Rice · Post by **Richard Rice** » 14 May 2012 4:45 am

Lane Gray wrote:Reece had suggested acrylic lacquer for the dings. Does that shrink like nitrocellulose?

In a word, yes. Different formulations will shrink at different rates, but lacquer shrinks, regardless. It still beats deep gouges, though.

As an example, take a close look at a 50 year old guitar finish. If it was nitro, it will have gone deep into the grain of the wood, and checked. This is due to a couple of things happening. First, lacquer continues to shrink and harden over the lifetime of the finish. It also gets more brittle. As the solvents continue to evaporate, the remaining coating gets smaller, tighter. Combine this with changes in temperature and humidity, or in rapid changes in temperature, and it will crack due to the slight expansion and contraction of the wood.

Nitro is more susceptible than acrylic lacquer, but all lacquers do this. Some more modern acrylic lacquers minimize this by having plasticizers added for extra flexibility, but the old school lacquers all do it.

Lane Gray · Post by **Lane Gray** » 14 May 2012 5:05 am

Thanks, Richard.
Should I still wait a couple weeks before sanding and polishing, then?

Richard Rice · Post by **Richard Rice** » 14 May 2012 5:16 am

Lane Gray wrote:Thanks, Richard.
Should I still wait a couple weeks before sanding and polishing, then?

If you can stand the wait, it will be a better repair. The longer you wait, the harder the repair will be (less difficult, but physically harder). If you rub it up to a great gloss too early, the gloss will dull a bit as the lacquer continues to cure. The harder the lacquer is, the easier it will be to level it safely, and the better the shine will be over time. I tend to rush my own stuff, but always leave customer repairs to cure longer. LOL

Richard Rice · Post by **Richard Rice** » 14 May 2012 5:20 am

A good way to judge your timing is a "sniff" test. Get your nose right over the repaired spot, and give it careful sniff. If you still smell paint, however faint it is, leave it alone. Once the smell goes away, generally you are good to go..

Jerry Kippola · Post by **Jerry Kippola** » 14 May 2012 5:34 am

Doesn't matter what kind of lacquer, what does matter is the solvent if you want complete amalgamation of the hit, lacquer retarder is the stuff-- it will weld weather checks also. Works on old lacquer, sometimes on really old lacquer. Super glue is used by some, but it doesn't actually melt the lacquer back together, and sometimes leaves air gaps. .

Richard Rice · Post by **Richard Rice** » 14 May 2012 5:53 am

Jerry, read the thread first. His original finish isn't lacquer. Your info is correct for a lacquer repair going onto original lacquer, but his surface is a different product. Chances are retarder will only slow his repair down by weeks with no benefit.

Jerry Kippola · Post by **Jerry Kippola** » 14 May 2012 6:07 am

Doesn't much matter. If it's catalyzed lacquer, or worse polyester, it is tough to repair, but i have used this for every type of finish w/ success. Usually superglue works best if it is polyester, but in order to make the surface polish a thin coat of lacquer on the surface does the trick. This kind of repair should only be done by someone familiar with the process, and if it is indeed lacquer, can be seamless---

Richard Rice · Post by **Richard Rice** » 14 May 2012 6:24 am

While I agree that a good repair can be made, the base is a product I am completely unfamiliar with, called "Styromica". I don't have any information on this product. My guess is that it will be unlikely to see the lacquer blend into it, much like trying to do a lacquer touch-up on some of the space-age finishes like UV cured, etc. I use retarder when necessary, but only in certain conditions such as high humidity, or when trying to reduce orange peel, blushing, etc. If Lane builds with a good quality lacquer, it will build and make good contact with the edges of the ding, regardless of the inclusion of retarder. He's just doing spot touchups, and will need to do multiple applications in order to build the new surface past level. Adding a retarder to the lacquer will only slow his curing time, and extend the drying time considerably.In the end, he will still need to overfill the dent, scrape it flush, and polish the area. Retarder will hamper the curing time.

Lane Gray · Post by **Lane Gray** » 14 May 2012 7:04 am

Multiple applications? As in don't put in a thick drop at once, but just a wee bit, let dry, another wee bit, let dry?
That makes sense

Richard Rice · Post by **Richard Rice** » 14 May 2012 7:09 am

Yep, that's the best way. Just a thin drop at a time, no more than three applications per day. Otherwise the surface seals up and slows the solvent from evaporating beneath. That will slow the whole process overall. You can just use a toothpick as an applicator- it doesn't take alot of product. Just a long time... Nothing more exciting than watching clear paint dry.. LOL

Jerry Kippola · Post by **Jerry Kippola** » 14 May 2012 7:44 am

If you try to fill it too fast, and with too much, when it finally dries the new lacquer will shrink and pull or crack to form air pockets, exactly what u don't want, as this will make it quite visible. This sometimes takes a month to happen. -that's one of the reasons i like the retarder--it slows the whole thing down, and softens the original surrounding finish. If i have the luxury, i will do the drop fills, and then let it dry for a month or two before filing and sanding the surface. Been doin' this stuff for 40 years, amazing what u can do with it -done right.

Richard Rice · Post by **Richard Rice** » 14 May 2012 8:19 am

Yep, I'll go along with that, Jerry..

Not sure what the retarder would do to the existing finish, though. Might attack it and make things worse, might not. I've been restoring antique since the '60's, now I mainly do guitar building, repairs and finishing for a living. I've seen lacquer attack all sorts of finishes, so I like to hit it hot and fast, with many coats spread over time. Finish coats with retarder lay out nice, but building up a deep gouge needs the lacquer to cure more quickly in my experience.

John Billings · Post by **John Billings** » 14 May 2012 9:14 am

Here's a repair a friend and I did on my '67 S-10. The ciggie burn was through the finish and into the wood. I removed the keyhead, and scraped from the point of the Gumby, down the center-line of that side of the keyhead casting, to the middle of the 10th string tuner. No sanding, only removing the finish and burn mark with a scraper. My friend then matched the color with powdered pigment stain, and sprayed WATER-BASED finish over the area.