Fix dents in guitar lacquer

Construction and repair of Classical Guitar and related instruments
magiPlay
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Fix dents in guitar lacquer

Post by magiPlay » Sun Feb 26, 2017 9:54 pm

Hi,

My Guitar finish is Nitrocellulose Lacquer
I played and I hit with my nail lacquer and were small white nicks as seen in the attached picture, how can I fix it and return the guitar to its good looks?

Thank you.
IMG_2758.JPG
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jim watts
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Re: Fix dents in guitar lacquer

Post by jim watts » Mon Feb 27, 2017 1:52 am

Yes, the dents can be fixed, but it's much trickier than it sounds to get a professional results.
To start with, if the wood is actually dented you must steam out the dents.
Then the finish is "drop filled" this where you take some nitrocellulose lacquer and fill the dents. You will have to do this several times over a week or so due to shrink back. Once you have a fill that's built up above the surrounding area, let the guitar sit for several weeks allowing time forthe lacquer to sink back. The longer the better.
Now comes the tricky part - you must level the fill with respect to the surrounding finish. If you finish is thin, and it should be, you risk sanding/polishing through the original finish, creating a problem that's much worse than the original marks.
From my point of view the dings in the picture are just marks from a well loved guitar and should be left alone.

Paul Micheletti
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Re: Fix dents in guitar lacquer

Post by Paul Micheletti » Mon Feb 27, 2017 7:30 pm

I also would leave those dents in place. They are so minor.

If you do decide to do the drop-fill method that Jim states above, there is a method you can use to level any bits of lacquer that is proud of the top surface. I use a single edge razor blade as a scraper for this. Put a few layers of masking tape covering the corners of the blade and all but maybe a quarter inch of the middle of the blade. Flex the blade with your thumb in the middle of the blade so that this uncovered area angles down toward the surface and the tape protects everything outside of the 1/4" of blade. A few very light scrapes will usually take it down a tiny lump nicely.

MessyTendon
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Re: Fix dents in guitar lacquer

Post by MessyTendon » Tue Feb 28, 2017 1:12 am

Put a tap plate on :) Right over those ugly dings...then you won't get much more.

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guitarseller345645
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Re: Fix dents in guitar lacquer

Post by guitarseller345645 » Tue Feb 28, 2017 1:53 am

We should have a corner for OCD guitarists (myself included) who do not like small scratches :)

Anyway I just tried wet sanding and buffing - turned out quite poorly but I learned a lot :)

I will wait a while before I attempt to restore it to former glory.
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Marcus Dominelli
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Re: Fix dents in guitar lacquer

Post by Marcus Dominelli » Tue Feb 28, 2017 3:55 am

Good advice from Jim and Paul,
It's a lot of work to go through all that process. If you take a very tiny brush with some thinned out nitro lacquer you can touch a bit into those dings.
This will get rid of the "white" spot, and make the dings much less noticeable. Then they can be carefully drop filled, making sure to not overfill the dings as to cause high beads or runs.

I would let the fill shrink back, and then probably leave it as is. I don't like rubbing out a nice, old lacquer finish that has the characteristic "ridges" between the high summer growth rings of the top, and the sunken in spring growth lines. Leveling and rubbing out the finish will make it all smooth and shiny, but you'll loose the ridging, which is what makes an old finish look good.
Further, rubbing out an area of the old finish in this manner will make the fixed area look "tampered with" which (IMO) is worse than having a few dings in the first place....

amezcua
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Re: Fix dents in guitar lacquer

Post by amezcua » Sat Oct 28, 2017 8:22 pm

I was trying to distinguish the difference between a dent and a ding. Maybe they don`t have official definitions so here is my version. A dent is where the wood fibres have been compressed or pushed aside. A ding is where a high speed knot has banged the surface so hard it has broken the wood fibres. Those fibres will not steam out into the original position.The jagged ends will be locked together inside the ding . In the picture above the dents show compression between the hard growth lines.The dents are in line with the fibre directions so the fibres have only been pressed sideways .
I filled in some very old dings this week . Mainly I was trying to clean dirt out of them .The dings did not steam out but the steam released most of the dirt onto the damp cloth .Then I used some ...Liberon Special Pale French Polish... into the holes. I used a thin pointed splint of wood .The French Polish shrinks back into the hole . I later filled the holes with superglue. The first time I noticed the superglue did not shrink . I used a razor blade to flatten the bumps
using the tape on the blade method .

A simpler way is to fill the hole with superglue and straight away use a razor blade to wipe across the hole and then wipe off any excess at the side of the hole . Folded paper tissue makes that quick and easy .
If a guitar is old and covered in masses of minute scratches it can be improved with a tiny amount of Violin Varnish. Lefranc & Bourgeois Copal Picture Varnish --Brilliant Gloss. (Can I edit the next bit. ) ###That is mixed I varnish to 2 Sanodor ,Windsor & Newton Sansodor (Low odour solvent). The exact dilution is something to experiment with . Better still is 1 varnish to 3 Sanodor ####.This mixture becomes wiping varnish which is very thin and will not collect spikes of fluff . It dries flat and shiny . It`s also very durable .###A 50/50 mixture will take forever to dry in colder weather. Read the articles about Wiping Varnish to get a better picture .
Last edited by amezcua on Fri Nov 17, 2017 12:45 am, edited 1 time in total.

Mark567
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Re: Fix dents in guitar lacquer

Post by Mark567 » Sun Oct 29, 2017 9:12 pm

Has anyone ever tried "Gluboost"?
I just moved my guitar to another wall and when the light crosses it I can see my nail dents under the bridge. I did that a couple of years ago and it took me a long time to get it out of my mind. Well, now I'm back to thinking about repairing them.
I know there are a lot of products on the market for these types of repairs, I was just wondering if anyone has tried this one or any other?
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simonm
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Re: Fix dents in guitar lacquer

Post by simonm » Sun Oct 29, 2017 9:47 pm

Do not put anything related to C.A. on the top of a finished guitar unless you are an experienced professional finish expert. Of course a professional finish expert would not ask this question and would probably not use C.A. :-)

Never heard of Gluboost before but a quick search suggests it is a C.A accelerator hence my response.
Last edited by simonm on Tue Oct 31, 2017 10:48 am, edited 1 time in total.

amezcua
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Re: Fix dents in guitar lacquer

Post by amezcua » Tue Oct 31, 2017 12:14 am

Did you mean "Do not "for CA on a guitar ? Can you say why ? Mechanically the dents repairs are having very little effect . For an old guitar there is no desire to hide what happened long ago .It just leaves a flat surface but there are visible marks .The most prominent mark(s) are where the small finger rested on the top while playing. It makes me think the guitar was owned by only one player .That area was worn and the wide grain pattern left a few threadbare lines between the hard grain . The CA was used in a pinpoint style .One of the repair videos shows a spray can used from a foot away . I can`r see the point of that

simonm
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Re: Fix dents in guitar lacquer

Post by simonm » Tue Oct 31, 2017 10:54 am

amezcua wrote:
Tue Oct 31, 2017 12:14 am
Did you mean "Do not "for CA on a guitar ? Can you say why ? ...
Yes, indeed. Thanks. I fixed it.
C.A. dries harder than any wood or other finish that I am aware of (except maybe some of the "poly" things). Maybe people who do it day in day out can manage to get it level. If at any future time someone wants to remove it, it will be difficult to impossible. On dark backs and sides C.A. is often used for dings during construction or fixing cracks. This is quite different from fixing a finished top. I have older spanish guitar and it is clear that some owner decided to fill nail marks and the like with C.A. - it is very obvious and no way to improve it.

amezcua
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Re: Fix dents in guitar lacquer

Post by amezcua » Tue Oct 31, 2017 2:05 pm

I feel a bit guilty now. My old 50s guitar is Spanish too .It did seem that the top needed some physical preservation though . It would not be correct if a museum was looking after it but this was not an expensive model originally . Optically the CA is very clear. Some wear marks ran into the rosette edge and that little bit is glowing with colour now .
One danger with scraping down CA with a razor edge is the strength of CA .If not scraped gently enough it might pull away what it is stuck to . Hence my levelling the wet CA with the razor straight after applying it . Guitars do not get the fervent attention that violins receive and there is a much more liberal attitude to surface preservation . But having said that there was a video of a priceless and rare violin being discussed by top experts and they laid it down on a grand piano without any cloth or padding below it. Beside the violin were cups of tea or coffee . That shocked me . And it was bad form to use a piano like that too.
About my ongoing renovation of the varnish . Yesterday evening I gave the top another thin application of 50/50 copal varnish and Sanodor . I looked at it this morning and noticed on the sides (not the top) near the neck there were some sticky finger marks from the previous day .I wiped them off with tissue paper and white spirits.This surface has already been wiped clean before with white spirits but the sticky fingerprints brought some more dirt off the surface. I have made violins myself and the surfaces have always been clean . This way to remove surface grime seems quite a useful discovery without any need for abrasives .

Alan Carruth
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Re: Fix dents in guitar lacquer

Post by Alan Carruth » Tue Oct 31, 2017 4:06 pm

It's generally best to fill with the same material as the finish, but that's not always possible. In this case, where the finish is nitro, that's the way I'd go given a choice.

Any time you get a dent that is simply compressed it's best to try to swell it out as soon as possible. The longer it sits there dented the more it 'gets used to' it, and the harder it is to swell out. Another big advantage of immediate action is that there's less chance that you'll get dirt in it, which can be difficult to clean out.

Most finishes are at least resistant to penetration by water; that's one of the functions of the finish. Nitro is brittle enough that it often cracks microscopically when it gets dinged and that admits some moisture. Thin finishes can be more easily penetrated than thicker ones, even if they're not cracked. Try putting some clean water over the dings and letting it sit for a while. Then warm up the area carefully with a hair dryer. Some finishes, such as shellac/FP will craze when heated, and the wood may have been sealed with shellac. Also, lacquers vary, so watch it closely! With any luck you can drive some moisture in through the finish with the heat; if so the wood will swell a bit. Often it's helpful to heat the surface until the water all dries off, and then, while it's still warm, put on some more and repeat. Even with the wood swelled up the dings may still be visible, but as the moisture dries out they should lessen. This may take a day or so.

If the wood fibers have been broken you will never get the ding to go away without surgery. Patching something like that in so that it's no longer obvious is one of the trickier aspects of repair, and you'll need to practice on something that you don't care about for some time to learn. You can fill it level with finish, but the actual damage will still be visible. Filled dings like that are in the category of 'clean dirt'; honest wear that shows the guitar is not simply a decorative wall hanging. So long as it's your guitar that's honorable. It's another story if you're trying to sell it as 'new'. Any maker can supply you with horror stories on that score.

amezcua
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Re: Fix dents in guitar lacquer

Post by amezcua » Thu Nov 02, 2017 3:13 pm

Using the diluted Copal Varrnish from France (see above) I noticed in the last few days that the temperature drop has slowed down the setting time . The first layer was dry in 2 days , when it was still a mild temperature. I did not need a pullover that day . When it got chillier the varnish needed 3 days to feel secure. But it`s not a sticky feeling. The (insect safe ) surface forms overnight .
I referred to the amouny of varnish needed for a guitar top earlier .That was only for one coat. Less than half a teaspoonful .I used the Sanodor to dilute as it`s not so stinky .The bottle is small and is only used for this purpose .Mainly the dilution is to prevent the (ubiquitous and invisible ) dust floating everywhere from forming spikes in the varnish .That gets like one step forwards and one step backwards again.It can drive you crazy and becomes a huge obstacle .
If you want to rub down the surface in between coats as they often do in violin making just use a cloth and linseed oil ,or even olive oil ,with some fine pumice powder .Clean all that off with white spirits afterwards .It leaves a matt surface ready to hold the next coat .You won`t need any sandpaper during this stage . Make sure to dispose of linseed oiled rags in a jar of water for safety .

amezcua
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Re: Fix dents in guitar lacquer

Post by amezcua » Fri Nov 03, 2017 11:18 pm

Two or three Tatay guitars on sale now have cracks in the top and back and some cruel use of sandpaper has added nothing to the character of the guitars .A minimal amount of crack cleaning would have been better than an inch wide scraping . One has had all the varnish sanded off and replaced . Such a shame to be so drastic .
Currently I am in the middle of sorting out a back crack that looks as if it was dropped straight downwards. It was repaired with some kind of rubbery glue.Inside are a few largish squares of thin plywood that serve as cleats .No minimal diamond shapes there .An unknown glue holds them in .It`s a pity they did not stay with the Hot Hide Glue it was made with .
The rubbery glue in the crack becomes softer with methylated spirits and I made a tool to remove it . I chose the thinnest feeler gauge from my car tools and cut the end to a wide claw shape .It fits in very narrow slots and teases out the glue without disturbing the mahogany . It may be the bottled hide glue that behaves like chewing gum when it`s set . All this needs good magnifiers .You can see movement if you press either side of the crack .
The feeler gauge I am using to fish out old glue is 0.06mm That`s about 1/20th of a millimetre. At the end of the crack there is no sign of glue but the gauge can pass straight through the back. I think diluted hot glue should get inside there and then I will need some cleats to pass the vibrations around .
Spruce cleats diamond shaped.16mm long,11mm wide and 3mm thick. That`s on e - b a y but too expensive to buy 100 .I won`t need that many but the correct shape is useful information . The grain has to run across the crack boys and girls .
Some repairers say the grain of a cleat should be parrallel to the crack But Michael Darnton is one of the best violin makers and repairers in the world and he recommends across the crack . His spacing is no closer than 7cms so that`s good enough for me .
The cleat shape can vary too . Have a look on Maestronet for a discussion about good ,minimal ,crack repairs .

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