2nd Build - Finishing Schedule

[MusicStudent1]

My first build was a challenge and I learned a lot. I made some mistakes and the paint sank down into the body and the sanding scratches are visible if the light hits it just right. It’s a beautiful, hard black thin finish And the guitar is well protected but it ain’t gonna win GOTM!!!

FAILED First Build Finishing schedule:

1. Sanded body smooth.
2. Applied water based grain filler, sanded, reapplied, sanded, over and over.
3. (Here is where I messed it up -) I bought some white primer to spray over the grain filled body. I sanded it, AOK! Then I looked at the can ...acrylic lacquer primer, not compatible with nitrocellulose lacquer. Can’t use my cans of nitro color and clear, now! I made the juvenile mistake of rushing and wanting to get on with it and didn’t read carefully enough!!
4. Sprayed and sanded multiple coats of acrylic lacquer, finally polished it to a gloss - done. Weeks later, the scratches started showing up.

2nd Build Proposed Plan:

1. Sand body smooth
2. Water based grain filler - more sanding
3. Seal the body with SHELLAC this time - not sure if I need multiple coats with sanding in between...thoughts?
5. Nitro color coat
6. Nitro clear coats - much time elapses - final buffing

Is my plan correct this time? I don’t want a thick, gloppy plastic finish but I also don’t want it so thin, it’s sinking back into the scratches (I will try to minimize scratches more carefully this time). It’s somewhere in between.



https://www.stewmac.com/luthier-tool...l-shellac.html

Thoughts? Comments? Criticism?

[Simon Barden]

Spray-on shellac is certainly recommended by quite a few luthier types, and is compatible with just about all finishes. In theory you don't need more than one coat of shellac, but that may depend on how smoothly it goes on. Non-water based filler may be better for not shrinking than water based. Otherwise you may be best to allow for some shrinkage and simple wait a full month after the colour coat goes on before sanding that back flat, and then do the clear coats.

Lets start with the basics and what is the body wood?

[MusicStudent1]

Spray-on shellac is certainly recommended by quite a few luthier types, and is compatible with just about all finishes. In theory you don't need more than one coat of shellac, but that may depend on how smoothly it goes on. Non-water based filler may be better for not shrinking than water based. Otherwise you may be best to allow for some shrinkage and simple wait a full month after the colour coat goes on before sanding that back flat, and then do the clear coats.

Lets start with the basics and what is the body wood?

Hi Simon, thanks for the quick reply. The body is basswood. Where I really blew it last time was after the grain filler . Not sure if I mentioned this but no paint sunk into any wood grain. What shows up is sanding scratches, so I hope he shellac sealer and nitro will give that professional finish.

I’m also going to fine sand everything before painting. This goes against something I read (the manual, maybe) about ideally having something for the paint to “bite” into....yeah, that didn’t work for me last time!

[Simon Barden]

Well you won't need grain filler with basswood, it'll just be a waste of time. But a sealer is recommended.

Certainly get the body as flat as you can before applying paint, though you really don't need to go above P180 or maybe P240. The main thing is to get rid of all the bumps and dips so that the whole surface of the body is flat (except for the curvy bits of course, but even they should be smooth with no high and low spots).

If you can start with a mist spray of the sealer, then if that shows up enough to be useful, you can use that to see all the dips that will need sanding down to. If not, a very light mist spray of a paint colour, just so that you can see where you've been when sanding. Sandpaper (from a roll) stuck to a flat piece of wood with double-sided tape is best for this. One that's longer than the body. Once all of that mist coat has gone, then you should have got a nice surface to start from.

Incidentally, what I've found out very recently is that the sanding' in 'sanding sealer' just means that it can be sanded, as opposed to a 'non-sanding sealer' which is meant to be applied thickly and not sanded at all. Its purpose is to seal the wood and stop the finish on top from sinking in. It may take two or three coats of the sealer to do this properly, especially if you sand back significantly (and so expose untreated wood). But it's far less coats than you'll need to get enough finish on for a level surface after sanding once the finish has stopped sinking in.

You can get the surface of the wood very flat and smooth, running through the grits up to P2500 if you want, but that won't stop you getting an orange peel surface that needs sanding back smooth and polishing. That's all down to the paint, the spraying techniques and the spraying environment. I don't know enough about the different paint types to know which ones prefer a slightly rougher surface to stick to. But even PRS don't go to very fine grits to get their wooden bodies ultra-smooth before adding the finish. That's all saved for the finish layers.

[MusicStudent1]

Well you won't need grain filler with basswood, it'll just be a waste of time. But a sealer is recommended.

Certainly get the body as flat as you can before applying paint, though you really don't need to go above P180 or maybe P240. The main thing is to get rid of all the bumps and dips so that the whole surface of the body is flat (except for the curvy bits of course, but even they should be smooth with no high and low spots).

If you can start with a mist spray of the sealer, then if that shows up enough to be useful, you can use that to see all the dips that will need sanding down to. If not, a very light mist spray of a paint colour, just so that you can see where you've been when sanding. Sandpaper (from a roll) stuck to a flat piece of wood with double-sided tape is best for this. One that's longer than the body. Once all of that mist coat has gone, then you should have got a nice surface to start from.

Incidentally, what I've found out very recently is that the sanding' in 'sanding sealer' just means that it can be sanded, as opposed to a 'non-sanding sealer' which is meant to be applied thickly and not sanded at all. Its purpose is to seal the wood and stop the finish on top from sinking in. It may take two or three coats of the sealer to do this properly, especially if you sand back significantly (and so expose untreated wood). But it's far less coats than you'll need to get enough finish on for a level surface after sanding once the finish has stopped sinking in.

You can get the surface of the wood very flat and smooth, running through the grits up to P2500 if you want, but that won't stop you getting an orange peel surface that needs sanding back smooth and polishing. That's all down to the paint, the spraying techniques and the spraying environment. I don't know enough about the different paint types to know which ones prefer a slightly rougher surface to stick to. But even PRS don't go to very fine grits to get their wooden bodies ultra-smooth before adding the finish. That's all saved for the finish layers.

Copy that, thanks for the info!

You reminded me that I used a product named “sanding sealer” on model rockets and wood pinewood derby cars when my kids were young. Wow...that was some evil smelly stuff! (I kept the kids away from it) I wouldn’t use it on a guitar, you’d need a ton of it, and I’m not sure how well nitro would work over it. Acrylic lacquer worked on those pinewood derby cars, lol...but I digress...

https://www.gravesrc.com/mid714-aero...ealer-4oz.html