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How long for nitro to cure before buffing
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Author:  ayavner [ Tue Sep 15, 2009 4:20 pm ]
Post subject:  How long for nitro to cure before buffing
Hey all,

I know from various sources, and a previous build, that there is a waiting period between the final coat of sprayed nitro and when it can be buffed out. I have seen this range from 2 weeks to a month. My info mostly comes from Stewmac's online info and Erlewine's Guitar Finishing Step By Step book.

My question is this - since the waiting periods seem somewhat conflicting, I think if I knew what end-state the finish should be at, I could make an informed decision when to start buffing, rather than just waiting 2 weeks or 3 or 4, just because this or that book or online guide says to.

Does that make sense?

thanks!

adam
Author:  Rod True [ Tue Sep 15, 2009 4:24 pm ]
Post subject:  Re: How long for nitro to cure before buffing
The harder the finish, the better buffing it will take. So the longer you can wait the better. 2 weeks might be a minimum but honestly waiting 4 weeks is better.

How's your patience?
Author:  ayavner [ Tue Sep 15, 2009 4:39 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Patience is fine, just trying to get a handle on what a "ready" coat would look/feel like so I will know that I have at least waited long enough for it to do whatever it needs to do (whatever that is).

Whenever i see a step (for anything) that requires a wait, I always like to know exactly what it is I am waiting for to happen, otherwise the wait seems arbitrary. (2 weeks? 4 weeks? Why not 25 days? 13 days?)

That said, i would like to be able to get this one done before my trip to Fur Peace Ranch in mid-October :D

thanks!
Author:  Cal Maier [ Tue Sep 15, 2009 4:44 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Rod's right!

2 wks. will be too short. You will get a lot of finish sinking at two weeks.
What I do and you should try, is at 3 weeks I do a basic level on the back and sides of the instrument. I take the sanding to 1200 grit, give it a quick buff a check to see how much, if any, sinking I get. Normally, I've found enough sinking that I leave it alone for another week, then I sand again from 1200 up to 1500 and buff again. This seems to be what works for me.

Cal
Author:  ayavner [ Tue Sep 15, 2009 5:06 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Ahhh so finish sinking is what we're looking for here?
Author:  Haans [ Tue Sep 15, 2009 5:20 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Really depends on whether you want it to look like a piece of glass in a year. I buffed my top on my latest 24 hrs after the last coat and the back and sides after 2 weeks. I want the top to look grainy, and the back can have a little grain show after a while.
Yea, I know, that's not the popular look... beehive
Author:  ayavner [ Tue Sep 15, 2009 6:02 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Hmmm, you raise a good point Haans. Obviously I want the finish to be as good as I can get it, however, not sure I am absolutely stuck on never having the finish show some texture. Last thing i want is a finish that looks like the 3 inch thick table tops in the bars with coins and stuff under them.. i do want to know that this is WOOD.

Starting to get a feel for what I am looking for, thanks all for sharing! Keep em coming!

adam
Author:  Rod True [ Tue Sep 15, 2009 6:05 pm ]
Post subject:  Re: How long for nitro to cure before buffing
There are other factors to consider too however. What is the atmosphere like where you are spraying/curing? To humid and it will take longer, to cold and it will take longer. Again, like guitar building, there are recommended conditions in which to let the finish cure. 45-55%RH and 70-75*F.

To get a good finish on a guitar, one has to apply a lot of coats in order to get the mirror gloss, perfectly level finish. The reason we have to wait so long for our finish to cure is becasue the VOC's are 'off gassing' leaving the solid portion of the finish. This why you get shrinking and with a thick finish (before leveling etc.) it takes a long time (much longer than 4-6 weeks too) for the VOC's to fully off gas. I've heard people say that nitro can continue to off gas for up to a year after the finish is applied.

So, that's why you need to let it wait longer. Of course this assumes you want to get that high gloss, level finish most of us desire.
Author:  TonyFrancis [ Tue Sep 15, 2009 9:58 pm ]
Post subject:  Re: How long for nitro to cure before buffing
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Author:  TonyFrancis [ Tue Sep 15, 2009 10:20 pm ]
Post subject:  Re: How long for nitro to cure before buffing
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Author:  Kevin Gallagher [ Tue Sep 15, 2009 10:35 pm ]
Post subject:  Re: How long for nitro to cure before buffing
30 days minimum.....45 days ideally. The finish needs to be a close to fully cured as possible before you
buff it. Don't forget that when you buff, it's of paramount importance that the finish isn't heated up at all.
If there is excessive speed on the buffing wheel, heat will build up, the finish will expand with it and will
then be allowed to drop into the pores when it cools again....not matter how well you've filled the pores.

Low heat and full cure should be chief considerations when deciding when to buff your nitro finish.

Regards,
Kevin Gallagher/Omega Guitars
Author:  TonyFrancis [ Wed Sep 16, 2009 1:22 am ]
Post subject:  Re: How long for nitro to cure before buffing
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Author:  Haans [ Wed Sep 16, 2009 6:35 am ]
Post subject:  Re: How long for nitro to cure before buffing
Another thing to remember Ayavner is that the sooner you sand and buff, the thinner the finish will end up and the fewer coats you have to put on. The sanding job you do has to be much better as every flaw will show, and I end up doing a lot of "pre-finish drop filling" around binding/purfling/abalone. Your pore filling on rosewood and other porous woods must be pretty dang good as sealer and lacquer are not finishing the job. A "flawless" finish does not mean that you cannot see the grain. Flawless is about defects.
It's an experiment to discover how many coats to apply and how long to wait for the look you want to achieve, but that's what it's all about. You get to decide the look you are after. Coming from building mandolins and varnish finishes, I prefer a thinner finish, but have made a compromise for guitars and am using a thicker (lacquer) finish. I go for the vintage look as that is the kind of instrument I build.
Author:  ayavner [ Wed Sep 16, 2009 7:51 am ]
Post subject:  Re: How long for nitro to cure before buffing
Wow, I am really glad I brought this up. some really great points of view and info here.

Though I would like to be able to wait long enough to be able to buff to the mirror glaze that will never shrink back, as I was wanting to try to have it done by mid-October, i may compromise on this one and give it 3 weeks and expect in a few years to see some grain telegraphing. Most tolerances were reasonably tight, so hopefully won't have any problems with it pulling away from binding etc.

This has been very educational, and now I have an idea of what some of the factors are when making decisions. Next one i will afford myself the luxury of a longer lead time, and can let it cure for months if necessary.

Enjoying the discussion! Eat Drink

adam
Author:  Haans [ Wed Sep 16, 2009 8:22 am ]
Post subject:  Re: How long for nitro to cure before buffing
Sure Todd. If you wait weeks or months before sanding and buffing, the finish will have shrunk down a lot, so you have to put enough on to level and buff. If you sand and buff right away, the finish is still very thick (but with fewer coats), you have a lot of thickness available to level, you can put on less finish thickness, level it out while it's still thick, buff, and then it shrinks down into the grain. The lacquer on the top of my new 12 measured out at .002" 24 hours after the last coat. I sanded and buffed it out to a high gloss right after that.
It's very evident with violin varnish as the finish is glass thick and shiny after you buff it, and is extremely thin several months later. Violin varnish (spirit) shrinks more than lacquer, but the same rules apply generally...the sooner you sand and buff, the less you can get away with putting on. The down side (if you want to look at it that way) is that the finish shrinks into the grain after it's buffed to a high gloss.
Author:  Glen H [ Wed Sep 16, 2009 8:32 am ]
Post subject:  Re: How long for nitro to cure before buffing
I've waited a week and also waited 2 months. It is hit and miss on how much shrinkage occurs later down the road. I just re-buffed a guitar I finished in January because the finish sunk back down in the pores. I had enough finish on, so I just re level-sanded with 1500 grit and buffed. It looks perfect now. I've used every kind of pore filler available, including CA, Z poxy and oil types. One way I've found that usually prevents the pores from re-showing them selves is to use epoxy to fill and apply plenty of coats of lacquer. Regardless of the wait time, this approach hasn't showed pores later. Too often, I'm aiming for a quite thin application of finish, and pores show (regardless of how long it sits after spraying finish). But, this is just what I have found.
Author:  Fred Tellier [ Wed Sep 16, 2009 4:06 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Quote:
Though I would like to be able to wait long enough to be able to buff to the mirror glaze that will never shrink back, as I was wanting to try to have it done by mid-October, i may compromise on this one and give it 3 weeks and expect in a few years to see some grain telegraphing


No matter how long you wait, if you have drop filled any defects they will eventually will show after a period of time. The nitro will shrink in relation to its thickness so that the drop fills will shrink below the surface eventually. Also along the binding or any wood joints there will eventually be a visible drop below the surface, and of course any any grain pores that were not fully filled with filler before the nitro is applied will also show. The long wait will reduce this and make it take longer to show.

If your nitro coated guitar is left in a case for a while you will still smell lacquer fumes even after a few years so the finish is still shrinking even then.

Fred
Author:  collinsguitar [ Wed Sep 16, 2009 7:37 pm ]
Post subject:  Re: How long for nitro to cure before buffing
Heres my two cents. Allow the finish to sit for two or three weeks after the final coat has been applied. Then do your wet sanding. After you are satisfied with the sanding and have achieved a uniformly dull finish, allow the instrument to sit for a week or more before buffing. This lets the newly exposed surface gas off and harden. Your finish will buff nicely after that.

MC
Author:  Hupaand [ Wed Sep 16, 2009 8:51 pm ]
Post subject:  Re: How long for nitro to cure before buffing
On those few occasions when my finish has worked, it has been when I waited long enough that the sandings were glassy, not gooey or gummy, or soft. Generally, about a month.
Author:  schrammguitars [ Wed Sep 16, 2009 10:23 pm ]
Post subject:  Re: How long for nitro to cure before buffing
I use McFadden's lacquer and buff it out to a high gloss after 5 days from the last coat with no problems. Prior to buffing I sand it with 800 dry, then buff with the dark brown Mazerna(sp?) then the fine grade.

Here is a sample: http://schrammguitars.com/siburg_009.jpg
Author:  Robbie O'Brien [ Thu Sep 17, 2009 4:12 pm ]
Post subject:  Re: How long for nitro to cure before buffing
schrammguitars wrote:
I use McFadden's lacquer and buff it out to a high gloss after 5 days from the last coat with no problems. Prior to buffing I sand it with 800 dry, then buff with the dark brown Mazerna(sp?) then the fine grade.

Here is a sample: http://schrammguitars.com/siburg_009.jpg


David,

In your opinion and experience, how is the shrink back factor with buffing out after 5 days? How does the guitar look a few months down the road?
Author:  Kevin Gallagher [ Thu Sep 17, 2009 4:30 pm ]
Post subject:  Re: How long for nitro to cure before buffing
When considering how many coats are necessary for the finish to be sufficient to be properly
leveled, sanded and buffed in its final stages, the process needs to be made clear.

When shooting lacquer, it's important to understand that the final wet sanding is not the only
sanding that's being preformed as the finish is built up and worked toward the end result in
its quality.

Once the first three coats are sprayed over the filled wood, they need to be sanded level and
flat before the next set of three coats are sprayed. Those next three coats are then sanded
lavel and flat before the final coats are sprayed.

The final few coats should be almost glass flat right out of the gun. There is very little
sanding necessary to level and have the final spray coats ready for the buffer.

I always wet sand to 1200 grit before going to the buffer where the heat is a factor that
will work in a negative way against the final result and quality in the finish.

It's impossible to wet sand...or dry sand for that matter....lacquer after only five days and
get a respectable professional gloss finish after only five days. The finish will always pull
in and shrink more than is acceptable since the finish still contains most of the solvents
that serve as the transport media for it. I love the look of an old Martin or Gibson, but
only on an old Martin or Gibson. I want my new guitars to look new....for as long as is
possible with a nitrocellulose lacquer finish.

All lacquers continue to pull and and shrink for quite some time after the guitars are
out of the shops or factories where they were built so it's not that long that they stay
looking brand new and flat and glossy anyway. That's one of the reasons I switched to
the UV cured polyester finish that never shrinks, never ambers and changes color and
never checks and cracks as the woods under it expand and contract with temperature
and humidity changes like the lacquers do.

Patience is a virtue that proves its worth in the finishing of fine guitars. Let the stuff dry
before you work it and the results will not only be better, but they'll stay better longer.

Regards,
Kevin Gallagher
Author:  rich altieri [ Fri Sep 18, 2009 6:13 am ]
Post subject:  Re: How long for nitro to cure before buffing
Really great information here.

Same things apply to polyester? I have been wrestling going between nitro and poly and have done a fair amount of lacquer but never poly.

My assumption with poly is that you spray it and its done - let it dry for a week and finish up.
Author:  Haans [ Fri Sep 18, 2009 7:06 am ]
Post subject:  Re: How long for nitro to cure before buffing
Kevin Gallagher wrote:

When shooting lacquer, it's important to understand that the final wet sanding is not the only
sanding that's being preformed as the finish is built up and worked toward the end result in
its quality.

Yes...


Once the first three coats are sprayed over the filled wood, they need to be sanded level and
flat before the next set of three coats are sprayed. Those next three coats are then sanded
lavel and flat before the final coats are sprayed.

Sure, with 600, just to get it flat...

It's impossible to wet sand...or dry sand for that matter....lacquer after only five days and
get a respectable professional gloss finish after only five days.

Depends on what you consider respectable and professional...

The finish will always pull
in and shrink more than is acceptable since the finish still contains most of the solvents
that serve as the transport media for it. I love the look of an old Martin or Gibson, but
only on an old Martin or Gibson. I want my new guitars to look new....for as long as is
possible with a nitrocellulose lacquer finish.

Again, depends on what you would consider acceptable. Guess French polish isn't acceptable...


All lacquers continue to pull and and shrink for quite some time after the guitars are
out of the shops or factories where they were built so it's not that long that they stay
looking brand new and flat and glossy anyway. That's one of the reasons I switched to
the UV cured polyester finish that never shrinks, never ambers and changes color and
never checks and cracks as the woods under it expand and contract with temperature
and humidity changes like the lacquers do.

I'm happy that you found your solution...flat and glossy forever...

Patience is a virtue that proves its worth in the finishing of fine guitars. Let the stuff dry
before you work it and the results will not only be better, but they'll stay better longer.

You obviously have a different idea of what looks better than I do...
You would probably hate mandolins with varnish.

Regards,
Kevin Gallagher
Author:  Kevin Gallagher [ Thu Sep 24, 2009 3:07 am ]
Post subject:  Re: How long for nitro to cure before buffing
Haans,
I do appreciate a nicely executed varnish finish on a mandolin and a beautiful French polish job. Those
finishes have a different set of final parameters or characteristics when it comes to what is acceptable or
considered of a professional quality when it comes to application and final results. I have seen, though,
varnish and french polish finishes that are on guitars from builder who are claiming much more expertise
than the finishes exhibit. They have been lumpy and inconsistent and sophomoric or amateur at best.

I did find my solution for finish as have many other builders as they're looking to end up with a finish
that looks new when the guitars are new. As Todd above, I also know that there has never been a nitrocellulose
lacquer finish that stays flat and glossy for very long after the guitar leaves the shop where it was built. My goal
was to offer my customers a durable finish that is flat and glossy and one that will stay that way for as
long as they own the guitars that I build for them.

I wasn't trying to take anything away from those finishes that inherently show some texture, have less gloss
and aren't as durable because there are plenty of players who love them and look for them. Most players
or guitar buyers do want a clean, smooth, glossy finish and those who don't mind less....even when the
builders try to cover their lack of finishing skill by saying that it doesn't matter....are less in number. That's
obviously why builders make so much investment in their finish and related equipment and techniques and
as many or more are sourcing out their finish work to any of the talented finish shops specializing in guitar
finishes. I've heard several builders explain away their finish quality with the old, "I ficus my time and energy
to tone and playability since they're what really matters." Yes, they matter a lot, but what attracts a player to
a guitar initially so that they can enjoy those all important aspects of the instrument is the appearance and
the quality of the finish.

I do have to say, though, that your tone in your previous post is the kind of thing that has chased a lot of
the seasoned and well known builders who used to frequent this forum away. They have better things to do
than argue about or defend the methods that have proven themselves and have made their guitars desirable
to a broad customer base. We come here to offer help and advice to those who are looking for it, not to argue
and have a condescending posture taken with us and our methods. I wondered where all of the fine builders
had gone when I came back after months, but learned quickly, at the hands of a few, why they're gone. It's
a real loss for those who are looking for help and not just to bolster their own reputation and to boost the
perception of their work and knowledge.

Regards,
Kevin Gallagher/Omega Guitars
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