Nitro Sanding Sealer Between Clear Nitro Coats

headly21

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I'm not sure whether doing this would even help my issue, but I'm considering using nitrocellulose lacquer sanding sealer over several dried (~10 days) coats of clear gloss nitrocellulose lacquer.
Why? Because, even though I prep-sanded smooth (or so I thought), grain/pore filled, and sealed this ash Tele body (with nitro sanding sealer) before I started applying clear coats of nitro lacquer, I can still see the grain pattern showing through. This is after I already shot more than *THREE CANS* of clear gloss nitro on this body. I guess the sealing and sanding job I did wasn't as good as I thought.

At this point, would applying sanding sealer on top of the clear nitro coats help build and smooth the surface more quickly, with fewer coats, before I resume shooting clear gloss nitro, ... or should I just continue to build up more clear coats of finishing nitro?
Or is it all awash and will I be spraying this body with the same number of total coats no matter which material I use?

I've read several threads, but I found nothing that addresses this question specifically. Thanks!!
 

Freeman Keller

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My limited experience with lacquer "sanding sealer" is that it does build thickness faster than lacquer itself and it does help fill pores, but still shrinks back just like lacquer does. I prefer not to use it now - I do my pore filling and try to have that as level as I can, shoot a couple of coats of vinyl sealer to seal any stains I might have applied and then go straight to the lacquer. Depending on conditions and how much reducer I have to add I'll shoot somewhere between 8 or 9 coats up to 18 or more. I typically shoot three coats per day and level sand each day before starting the sequence.

I don't think it would hurt to spray sanding sealer at this point, it still should melt in to the previous lacquer. As far as the amount you have used, here is what StewMac says of their lacquer

How many cans do you need?
  • Electric guitar neck: No sealer, 2 to 3 cans lacquer
  • Solid body electric: 1 can sealer, 3 to 4 cans lacquer
  • Acoustic or archtop guitar: 1 can sealer, 4 to 6 cans lacquer
 

Peegoo

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Therre are several ways to approach this problem.

I would allow it to cure for at least three weeks, level sand with 220, and apply several successive thin coats of shellac. Sand that level, and apply a few more coats, followed by level sanding to prep for nitro topcoats.

Shellac builds quickly, level sands easily, and is totally compatible with nitro under and over it.
 

headly21

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My limited experience with lacquer "sanding sealer" is that it does build thickness faster than lacquer itself and it does help fill pores, but still shrinks back just like lacquer does. I prefer not to use it now - I do my pore filling and try to have that as level as I can, shoot a couple of coats of vinyl sealer to seal any stains I might have applied and then go straight to the lacquer. Depending on conditions and how much reducer I have to add I'll shoot somewhere between 8 or 9 coats up to 18 or more. I typically shoot three coats per day and level sand each day before starting the sequence.

I don't think it would hurt to spray sanding sealer at this point, it still should melt in to the previous lacquer. As far as the amount you have used, here is what StewMac says of their lacquer

How many cans do you need?
  • Electric guitar neck: No sealer, 2 to 3 cans lacquer
  • Solid body electric: 1 can sealer, 3 to 4 cans lacquer
  • Acoustic or archtop guitar: 1 can sealer, 4 to 6 cans lacquer
Okay, so I'm not so far off the mark with using a 4th can of clear coat lacquer. I was getting concerned because I recall reading somewhere that one or two cans would be enough for a solid body.
I actually just block-sanded the dried finish with 800-grit, which did smooth things out quite nicely, and I just shot another heavier coat of clear. Nice warm dry day here, which is rare in Central FL, so I'm taking the opportunity to spray. Thanks!!
 

headly21

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Therre are several ways to approach this problem.

I would allow it to cure for at least three weeks, level sand with 220, and apply several successive thin coats of shellac. Sand that level, and apply a few more coats, followed by level sanding to prep for nitro topcoats.

Shellac builds quickly, level sands easily, and is totally compatible with nitro under and over it.
Thank you! The existing finish was already quite dry and hard, so I actually got good results by taking down the shine with 800-grit; then just shot a heavier coat of clear nitro again. I'll likely finish this 4th can, let it cure for several weeks, and start wet sanding.
As per my reply to Freeman Keller, I was misinformed about how much clear lacquer is sufficient for a guitar body.
 

Boreas

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Okay, so I'm not so far off the mark with using a 4th can of clear coat lacquer. I was getting concerned because I recall reading somewhere that one or two cans would be enough for a solid body.
I actually just block-sanded the dried finish with 800-grit, which did smooth things out quite nicely, and I just shot another heavier coat of clear. Nice warm dry day here, which is rare in Central FL, so I'm taking the opportunity to spray. Thanks!!
How much lacquer you end up using is usually dependent on how smooth you get the sanding sealer coats. If it isn't baby-bottom smooth before switching to nitro, you won't likely "fill" it with just few cans of nitro and sanding. It usually requires many additional coats to spray and sand. The key to reducing material is to get the pores and grain filled prior to switching to nitro. You can still get a nice finish, but with additional nitro and sanding.

I usually end up using LESS than what S/M recommends for necks, but I don't much care for glass-smooth necks and usually end up de-glossing them somewhat. AND they are usually rosewood, so I don't spray that part!
 
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Freeman Keller

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Okay, so I'm not so far off the mark with using a 4th can of clear coat lacquer. I was getting concerned because I recall reading somewhere that one or two cans would be enough for a solid body.
I actually just block-sanded the dried finish with 800-grit, which did smooth things out quite nicely, and I just shot another heavier coat of clear. Nice warm dry day here, which is rare in Central FL, so I'm taking the opportunity to spray. Thanks!!

I usually figure at least a quart of lacquer to finish a guitar, most of the time it takes more. I apply 2 or 3 coats of finishing resin on porous wood, then a couple of coats of the vinyl sealer. I sand to 320 between groups of coats, I don't think there is a need to go finer.

On acoustic instruments I try to keep the finish pretty thin - a dozen coats is usually enough. Electric instruments gets more, I'm going to spend a little more time wet sanding and buffing.

The important thing to remember is that I try to have the pores filled before sealing and not rely on the lacquer for that function.
 

old wrench

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I use ash pretty often for my guitar bodies.

Ash is an open-grained wood and it can really suck up a lot of finish, especially if you are going for a traditional flat and smooth lacquer finish.

And "swamp ash", which is the type of ash I use, is a softer, more porous variety of ash than the harder northern variety

A real thorough job of grain-filling and leveling followed by enough coats (3, 4, or maybe 5, it all depends) of sanding sealer cuts down on the number of finish coats of clear gloss, but it takes a lot of coats of lacquer to end with a nice, flat, and shiny finish on ash.

A characteristic I've noticed of the combination of ash and lacquer is that since the lacquer finish penetrates into the wood, it seems like there is an exaggerated effect of how the finish pulls back or sinks into the wood as the finish continues to dry - most of that "sinking in" occurs in the first couple of weeks, but it continues to sink in for quite awhile.

Some of my early lacquer finish jobs looked perfectly flat and smooth when I finished buffing them out, but after a couple of months you could plainly see the grain pattern pushing right through the finish - it's not a bad look, in fact, I actually like the way it looks, but its not a traditional flat, smooth, and shiny lacquer job.

So, I've learned to do a more thorough job of grain-filling and leveling, and to also add a few more finish coats if I'm going for that traditional, classic-looking lacquer finish.



For your guitar body in particular - If you are liking the way your finish job is heading, I'd stick with using clear gloss for the additional coats instead of sanding sealer.

Sanding sealer does build faster than clear gloss, but sanding sealer doesn't seem to have the same clarity - and, I don't think it dries quite as hard as clear gloss either.

.
 

Silverface

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grain/pore filled
What brand - and same with the sanding sealer and finish lacquer.

How are you spraying? How thick is each coat? A single coat should be very transparent - if you are going for full coverage/flow with a single coat it's far too thick.

Did you do practice applications of the full system on scrap before starting to work out all the spray techniques and fine-tune the application? If not, I strongly suggest doing that before going further.
 

Sea Devil

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I find that just over one can is usually enough for a body. When I started, it took just over three.

The Stew-Mac people know that beginners use too much paint and advise accordingly.
 




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