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Hi all.

I've got a scratch in the the spruce top of a guitar I just finished for a friend which is pretty annoying. Its a couple of inches long on the lower bout. Can I repair or should I re finish?

I've tried spraying nitro without much success , I really like the slow and non toxic technique of tru oil and love the look but it just seems too soft. I've also sprayed a shellac burst and then tru oil over the top which looks great but i suspect won't wear well. Tru oil is also really cheap which is a major factor for me.

How does min wax poly compare? Is it as thin and natural looking as tru oil?

Should I just learn to French polish?

Help and advice appreciated as always.

Mike

Did you wetsand the top? If so, you'll have to sand the whole top, or there will be witness lines.
If it's TruOil on the scratched top, I'd sand it with 400 grit, and then put several coats of TruOil over it.
If it still shows, you'll need to sand the whole top and put on a couple more coats of TruOil.
TruOil is actually a little tougher than FP if done correctly.
I've never used the wipe-on poly, so I don't know how that compares.

_________________
A man hears what he wants to hear, and disreguards the rest. Paul Simon

My experience with min wax poly is that it does not stand up (on necks at least). However I only tried it on one guitar so perhaps it was me, not the finish.
Pat

_________________
There are three kinds of people:

Those that make things happen,
those that watch things happen,
and those that wondered what happened.

Hmm. How does nitro compare in hardness? I've just left the tri oil with its final sheen. No sanding. Do I try to fill and then and or sand the scratch away and then build layers back up?

Nitro is harder than TruOil, but I've only used nitro once, so my experience with nitro is limited.
It's good that you didn't sand, that actually works best with TruOil, for me anyway. I'd do a light scuff sand, and not really try to sand out the scratch, and then a couple of coats of TruOil. With any luck it will cover and blend, and you won't have to do the whole top.
Finish is not easy, and an invisible finish repair is the most difficult part of the craft. Good luck!

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

TruOil is probably hard enough to satisfy anybody if you give it time to cure. I've told this story before, but I will repeat it here because it is true. I bought a white pine (read soft wood) unfinished bedside table in 1980 from a firm in Arlington,Va. I finished it in natural color with TruOil. 35 years later the finish on the top/sides/drawer front is still intact, not crazed and nice and shiny. TruOil was developed and marketed primarily to be used as a gunstock finish. It promises a tough finish that is attractive and easily repaired if damaged. I've used it on gunstocks and on guitars without any issues. A TruOil finish can be satin or glossy. Whatever appearance you want, you can produce AND it feels good to the touch. Now, my bedside table is not drug through the brambles like my rifles might be but it has taken a beating from spilled coffee, booze (which would ruin a french polish finish) and whatnot. So I recommend it.
Cheers,
Tom

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I spent most of my money on women, guitars and whiskey, the rest I wasted.

From what I can tell I doubt if Tru Oil is as hard as Nitro. I doubt that it's as hard as Shellac. Back in the year 2002 I finished my personal guitar in Tru Oil. To me it was a new finish although I certainly wasn't new to Oil based finishes. I had the guitar for around 4 years before someone offered me money and my resistance was low. The Tru Oil held up OK although there certainly was a bit of dulling where the arm contacts the instrument.
A lot of these finishes need months to really set up, as stated by the previous poster. That's true with shellac and it's more true of Oil based finishes. You need to give them time and quite a lot of it. The alternative to Tru Oil is one of the Danish Oil type finishes but make sure it contains a resin. One commonly used is the Liberon finishing Oil. I use the Coloron Danish Oil (made by Ronseal, I think) - probably only available in the UK. It clearly states on the tin that it's a blend of Oils and resins, almost certainly Tung (I can smell it) and modern synthetic resins. 16 or so wipe on coats and you should be able to obtain full gloss. Then it's a matter of giving it a couple of months before handling. You can handle it after a week or so (not recommended) but the longer you leave it (within reason) the harder it will become. The best way to test these finishes is by addressing the spill over on the tin/bottle. Not the really thick accumulated stuff but that which happens to form a relatively thin film. I've had an old Coloron tin for 5 years and the contents went solid 3 years after I bought it. It's the film that spilt over years previously that I test with my finger nail. Underneath this spilt varnish is the actual metal/tin, so there isn't much chance of compressing the surface underneath. It seems to me as though it's a fairly hard but durable/tough material, although not chippy. It's not going to be as hard as Nitro but then again it's probably never going to suffer finish cracks.

French polish probably is a bit harder than TruOil, but I believe TruOil is a bit tougher. Neither is as hard or tough as nitro.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

Here's one guy's take on how to repair Tru Oil

http://www.bloodstoneguitarworks.com/new-page/


I don't use shellac --but I must say this is the first time I have ever heard it characterized as hard (yes hard as brittle/chip prone) but not hard as in scratch prevention or tough. Seems conventional wisdom at least, has deemed lack of durability the main (and maybe the only) short coming of a French Polish finish -- labor aside.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Most finishing materials that are hard have a tendency to be brittle/chippy. I'm not sure Shellac is as chippy or brittle as some.
It's certainly not soft. Try scratching a Shellac button, after all that is the base material when all the alcohol has gone. That's a better test than trying to scratch shellac that has been put on wood. Most of the time when people test finishes on wood they are simply compressing the wood that is underneath the finish. A Shellac button doesn't seem soft to me. Of course it's nearly always French polished on (at least with guitars it is). French Polishing almost guarantees that the finished Shellac film is painfully thin. That may have some bearing on how folk view it.
Then there is the fact that a small percentage of folk seem to be able to strip a Shellac surface in a matter of weeks, often thought of being due to alkaline sweat. Certainly alkaline solutions dissolve Shellac readily. I'm fortunate in that I don't seem to affect shellac much at all.

I've had some luck with Ace Hardware poly urethane varnish. It can be thinned 50/50 with odorless paint thinner and then wiped on. It gives a finish that is durable but looks something like a penetrating oil varnish. It dries fairly quickly and feels good. It's not as beautiful as a Liberon oil finish but it doesn't have some of the penetrating oil problems.

_________________
Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com