Finishes, drying and curing

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09-05-2016, 09:25 PM
dingobass

Finishes, drying and curing

Just about every type of finish you can get will say something along the lines of "dry after 6/ 12 or 24 hours"..
Where as this may be true, the finish wont be cured.

Curing is the process of gassing off of all the solvents as well as the cross linking polymerisation.
This takes time, typically 20 - 30 days.

So, regardless of what finish, be it Nitro, rattle can Acrylic, Poly or even Dingotone you are best served to leave it for a minimum of 20 days before final cut, polish and assembly.
To do so before this curing time is to court disaster.

If you want a finish that you can spray cut and polish and assemble in one day, you will need to look at UV cured finishes. Expensive set up costs, highly toxic and not easy to get right without a lot of practice.

Remember, building a Guitar should be an exercise in patience..
The more time put in during the sanding and finishing process, the better the result.

Typically it takes me around three months to complete a build, whether it be a kit or one of my custom builds.
Most of this time is spent watching paint dry.... but the end results are well worth the time.
09-05-2016, 09:38 PM
Brendan

Sagacious words of wisdom. As a mod and judge, I've seen a few rushed jobs on the forum - best thing is to step back and take time - give it a chance and the finish will be heaps better.
20-10-2016, 01:33 PM
DrNomis_44

This is something I should pay close attention to, since I'm equally as guilty of rushing things and not excercising patience, and I'm humble enough to freely admit that.
03-02-2017, 09:42 AM
MusicStudent1

Basic Nitro Finishing Questions

Greetings Dingobass and any of you other veteran builders!

I'm going to start an EX-5 basswood body bass guitar build in a few months when the weather here improves. I am prepared for a 3-4 month build, no problem. I'm a little confused on the process. Is this right or wrong:

1. Sand the body with sandpaper working up to the higher grits.
2. Rub in a grain filler, sand smooth. Do this several times.
3. Use sanding sealer, sand smooth.
4. Spray color nitro coat, wait until it cures, sand. (How long between coats does one wait to sand?)
5. Spray again, sand, repeat, spray, sand again, how long does one wait? 20 days between coats???...or is the 20 days just for the FINAL polishing?
6. Spray clear coats, sand, spray, sand, repeat, final polishing.

Does anybody use primer? Grain filler and sanding sealer seem to make primer unnecessary.

I can't find any straightforward instructions on how to do a solid black nitro paint job.

Oh yeah....drill the holes for the bridge BEFORE wet sanding (and risk wood swelling....I saw on a Pit Bull video that a workaround is a drop of lacquer in the hole) or after guitar is finished (and risk damaging the finish on the drill press)?

Sorry if these are stupid questions. I am a bit of a noob.
03-02-2017, 10:20 AM
Zandit75

You missed the most important, and vital first step....
Do a mock build, and check that the scale length, and alignment is correct, and ensure everything that's supposed to be in the kit is there.
There's no point doing everything else if your neck pocket is out is out of alignment, or the neck doesn't fit etc.
Check out the recommended build process here >> http://www.buildyourownguitar.com.au...splay.php?f=57
03-02-2017, 01:40 PM
MusicStudent1

Quote:

Originally Posted by Zandit75

You missed the most important, and vital first step....
Do a mock build, and check that the scale length, and alignment is correct, and ensure everything that's supposed to be in the kit is there.
There's no point doing everything else if your neck pocket is out is out of alignment, or the neck doesn't fit etc.
Check out the recommended build process here >> http://www.buildyourownguitar.com.au...splay.php?f=57

Oh, I failed to mention I did an unboxing video, inventory, and mock build already. We're good to go. I'm super impressed with how tight the neck fit is. It's light years ahead of the old bass I'm playing now. Yeah...the EX-5 is a keeper.

Brother, MY most important step is making my lovely bride happy this weekend by getting my garage in shape for this project!!....I'm ashamed to say it's looking pretty bad but I digress....I can't start spraying anything until it gets warmer anyway.
03-02-2017, 01:46 PM
Zandit75

Haha, yes that bit of information would have been helpful, so I don't look like a know-it-all!!
Good to see you have the "Happy Wife, Happy Life" mantra down pat!!
I can't help much with the other info, I haven't down a solid colour build yet, and I certainly have not used nitro.
Hopefully someone will chime in soon for you!
03-02-2017, 02:01 PM
MusicStudent1

Quote:

Originally Posted by Zandit75

Haha, yes that bit of information would have been helpful, so I don't look like a know-it-all!!
Good to see you have the "Happy Wife, Happy Life" mantra down pat!!
I can't help much with the other info, I haven't down a solid colour build yet, and I certainly have not used nitro.
Hopefully someone will chime in soon for you!

Absolutely! 😀 I'm reading all kinds of stuff about nitro. Not much is there about the drying time needed between coats. I want to go with nitro because it's "traditional", used by Gibson, and looks very high quality when done right. The kit is worthy of the best finish possible. I'm also agonizing over buying a better bridge before I start drilling holes. The one it comes with seems just OK...I'm on the fence about it. The kit also seems worthy of a Graph-tech nut but I can do that after completion.

I might get that book by Dan Erlewine from the library about guitars. I read it years ago and recall his in depth discussions about the process.

I'll keep you posted, thanks for the reply!!!!
03-02-2017, 05:47 PM
Simon Barden

There's a lot of different info out there about suggested time between nitro coats. Minimum time seems to be about 20 minutes, maximum time 60 minutes. Normally 3 coats a day maximum, then let it dry and harden overnight. Very important to let the finish harden before you attempt to polish it. 1 week is the bare minimum, but 2 is more normal and 3 would ensure that it's ready. High humidity slows drying times, so if that's the case, go with the longer drying times. Too hot a day (say 35°C+) can be a problem as the spray can dry in the air and go on rather powdery. Too cold (generally below 14°C), or too humid when spraying, and moisture can/will get trapped under the finish and turn it misty. So it's best to spray with the temperature in the twenties and with reasonable levels of humidity (if possible).

Note that Nitro is hazardous to health, and you need to buy a vapour mask and should cover up as much as possible to stop it getting onto your skin - wear rubber gloves or disposable latex or vinyl ones. If you can smell the spray with the mask on, then it's either not seated well enough on your face, or the carbon filter is all used up and it needs replacing. The vapour is also explosive, so use a well ventilated area and no smoking or sparks. The finish touch dries in about 5 minutes, so if you are spraying in a garage (to avoid as much dust as possible), then I'd spray, shut the outside door for 5 minutes, then open the door again for ventilation to disperse the fumes. Any door to inside the house should remain closed as you don't want the fumes inside.

The StewMac/Dan Erlewine Guitar Finishing book is a very good reference book, but it does spend a lot of time on talking about how to match various classic (mainly Gibson and Fender) guitar finishes. A lot of the information is already available on the StewMac website - you just have to look round for it.
06-02-2017, 03:19 PM
MusicStudent1

Thanks for the very informative post, Simon and thanks for taking the time to write it. I'm going to build a spray booth out of some scrap lumber and am going to spray in the garage. I agree with everything you said and own a great painting ventilator mask.

Still one question. The time between coats. Does that include sanding between coats?

Or does one spray a coat, simply wait an hour or two, spray another, repeat, then wait 2 weeks or more for sanding, polishing, etc?

Yeah....I need to buy the book.
06-02-2017, 04:03 PM
Brendan

Music Student - check out the videos from Jarrod under the guides section - http://www.pitbullguitars.com/videos/ - you're looking for Hi Gloss Finishes 1 & 2. Jarrod has built some amazing guitars (kits and scratchies) and his spray finishes are amazing. He ended up building a spray booth using a second hand water tank from memory...

#1 is here: https://youtu.be/IlJs-JCKRKE
06-02-2017, 05:24 PM
Simon Barden

You'd normally sand after any grain filling and then after sanding sealer coats.

If you're going for a solid colour and using a primer, then you'd spray several primer coats, enough to sand that back flat, then spray your main colour coats. You'd probably sand that flat and then do any clear coats, sand that back and polish once cured.

With a sunburst, you don't want to sand the finish if you can help it at all, so you'd spray all of that, then all the clear coats, before sanding it back and polishing once cured.

What you might do at the beginning of each day's spraying, is do a 'drag sand' - very lightly wiping the surface with some fine sandpaper just to remove any protruding dust particles or hairs in the finish. You need to let the finish dry quite hard before doing this otherwise it's amazing how much (sub-surface) wet finish a dust grain can take with it, so never do this shortly after spraying. Also, if you get an obvious paint run, then you'd probably want to sand down that small area - but again, the finish needs to be dry otherwise you'll break through to the wet layer underneath which is when it all starts to go wrong. Every time you spray, the solvent in the lacquer/paint 'melts' the layer(s) beneath a bit, so there's always a thicker soft layer underneath the apparently dry surface than you'd think.

It takes a while for all the solvent to finally evaporate and the finish fully harden. The harder it is, the better it will polish up. You can sand it down after a few days (the extra surface area provides by all the tiny score lines will help promote solvent evaporation) but ideally wait 3 weeks before the final polish.
07-02-2017, 09:11 AM
MusicStudent1

Thanks for the replies. Yes, I watched the videos and that's what gave me the idea for the spray booth. Mine will be simpler but it should keep dust off the drying paint. I also didn't know on a sunburst finish one does not sand between coats.

I intend to do a gloss black nitro finish. I'm just trying to do a good job and avoid burying it in paint as one sometimes sees on inexpensive guitars.

I may use sanding sealer from stew mac followed by a white primer before spraying the first coat of black. I'm still a little confused though. If I spray a coat of black, I need to wait weeks before lite sanding and spraying another coat? That's what it sounds like. Hey, whatever it takes, I'm not going to rush it.

I have some reading to do, thanks for the info.
07-02-2017, 06:11 PM
Simon Barden

No, the long wait is only at the end after you've put your clear lacquer coats on.

Normally recommended a maximum of three coats a day, with a 20-60 minute drying time in between each coat. After you've finished the primer coats, I'd wait maybe two days before it's hard enough to sand it down flat down nicely (If it's not hardened enough before you do this, the primmer will still be contracting as it dries further and after a bit more time the the surface won't be flat). Then once flat (you need to look at it with a light shining on it at a low angle to see any small hollows in the paint that still need removing), you can start to spray your top coats on.

If you see any obvious hairs or dust marks stuck to the finish, then do that light drag sand at the beginning of each day before spraying, so that the paint's hardened overnight.

Just FYI, the reason you don't sand a sunburst finish until it's covered in clear lacquer is that the actual fade/burst area is made up of millions of very small lacquer droplets. These will have come from the very edge of the spray, so won't have hit the surface very wet at all. so have very little solvent in them and so don't adhere to the paint below well. If you try and do any sanding on these areas, those small drops come away from the surface very easily, and instead of a 'burst, you are left with clearly defined edges between the different lacquer colours. I found this out the hard way!
10-12-2020, 01:27 PM
IngridM

1 Attachment(s)

How to sand back top coats with uneven layers?

Quote:

Originally Posted by Simon Barden

No, the long wait is only at the end after you've put your clear lacquer coats on.

Then once flat (you need to look at it with a light shining on it at a low angle to see any small hollows in the paint that still need removing), you can start to spray your top coats on.

Simon, when spraying top coats what's the procedure and timeline of sanding/respraying?

My stepson has made a Van Halen paint job and is up to the top coats.

Attachment 38378

I'm presuming it would be good to use the top coats to level out the surface by sanding back between top coats? (Or is this not how top coat works? Total newbie here...!)

The white parts has only 5 total layers, the red 7, the black {not pictured} has 9).

Thanks in advance!

Getting the 14 yo to wait out a 30 day curing time is going to be interesting...
10-12-2020, 04:07 PM
Rabbit

Quote:

Originally Posted by Simon Barden

Note that Nitro is hazardous to health, and you need to buy a vapour mask and should cover up as much as possible to stop it getting onto your skin - wear rubber gloves or disposable latex or vinyl ones. If you can smell the spray with the mask on, then it's either not seated well enough on your face, or the carbon filter is all used up and it needs replacing. The vapour is also explosive, so use a well ventilated area and no smoking or sparks.

This goes double if you are using automotive 2k clear. You need a full face respirator with carbon filters. A half mask is fine for base, but for clear , the nasties in the hardener can be absorbed through the eyes. Wet sanding can be done after a couple of days, but to fully cure without the aid of baking takes 8 weeks.