What would happen if I sanded lacquer before it fully cured?

[Jeremiah]

I'm experimenting a refinishing project, and I'll soon be spraying the final coats of clear acrylic lacquer over solid black.

I am aiming for a matte/satin finish, so intend to sand the clearcoat with either fine sandpaper/micromesh or very fine steel wool.

I know the lacquer is meant to be left for at least 2 weeks to cure before any sanding or polishing, but I'm very impatient to get the guitar together and playable. :sad1:

So what's actually going to happen if I sand the lacquer to matte  without waiting the 2 weeks? Will it be weaker than it should be, or would dust from the sanding stick to it and stop it getting a good finish?

 

[BigBeard]

I think you will end up with a mess.  I bet it isn't hard enough to sand and you'll end up with more of a problem, which will mean more sanding, spraying and waiting.  I know if you get on poly too early it doesn't rub out very well, it is still too soft, I am guessing laquer is the same way. 

 

[dmraco]

nitro will cloud up and get gummy...better off to wait.

 

[Jeremiah]

Hmm, I've just read on the side of the paint can that it should also be left for 2 weeks before sanding... so to do it properly, I'd have to wait 2 weeks, then sand the paint, then spray lacquer and wait ANOTHER 2 weeks before I can touch that.

I suspect the guitar will never get sanded or lacquered.. I'll probably just put it together the way it is now, with the matte black coat, and mean to do the lacquering at a later date but never get round to it.

nitro will cloud up and get gummy...better off to wait.

By the way, it's acrylic auto paint not nitro.

Edit: since I'm also spraying the headstock, I might experiment with that, and if it messes up it won't be too big to sand back and start again.

 

[Keyser Soze]

Just spray a piece of scrap material (or two) that way you can experiment without fouling up any of the guitar.

When the finish is not properly cured the abrasive doesn't so much cut the surface, instead it sort of smears it. 

But on the plus side acrylics tend to cure rather rapidly, since you do not intend to bring the surface back up to a high gloss you might be able to get by with a shortened cure time.

Haste doesn't guarantee poor results, but when they happen it does guarantee an early start on regret.

 

[Jeremiah]

Yeah, I think it's a much better idea to experiment on a piece of scrap wood so I'm gonna do that.

This will allow at least a few days for the paint on the guitar to cure.

I've just sprayed the last coat of matte black and I love the look so much already that I don't want to sand or lacquer it at all!

 

[dmraco]

sorry...I thought you were talking NITRO.

when I have used automotive, I have sprayed all my lacquer at once, then sanded smooth.  I have done 3 motorcycles this way with no issues...I used House of Kolor products.

You can spray, sand, and respray but I do not see the real benefit to that.  If you do, let it dry per the manufacturers instructions.  I would sand with around a 600 grit so the next coats have something to grab onto.

Remember with automotive, you can sand and polish at about the 2-3 week period.  If you wait much longer the stuff is hard as nails and tough to polish.  Also...DO NOT WAX for about 2 months...this will screw up the final cure process.

good luck

 

[DesmoDog]

What kind of modern auto paint needs WEEKS to set up? Body shops don't wait weeks, they wait hours. Granted they bake things but still.

I'm only experienced with House of Kolor products but WEEKS of set up time? Really? 24 hours is the longest I've ever waited before buffing a finish, maybe 12 for wet sanding.

I just checked the HOK stuff - on their laquer clear coat the quote 12-24 hours before sanding.

And not for nothing, but you can get satin and flat clear coats... IMHO a sanded finish will look scratched, not flat or satin-ee. I'm basing this purely on what I've seen after wet sanding so I may be mistaken but it's not the way I'd go about getting a flat black finish.

 

[nestron3030]

i did it to early once and iit seemed fine at first but after a couple weeks the lacquer shrunk so my finish wasn't as leveled i put flamed maple venner on the top and after the couple weeks of me playing it after final sanding and polish the center line where the veneer joins you can see how the lacquer is not leveled there

 

[-CB-]

Ok... lacquer 101

This applies to acrylic and nitro lacquer

Lacquer cures by evaporating solvents that allow it to be liquid.  The rate of evaporation depends on whats under the lacquer, how thick the lacquer is, the temperature, the humidity, the air pressure, etc.

Because of evaporation, lacquer shrinks as it dries.  <--- re re re read that

You need to allow adequate shrink time, or you'll sand it level, and it will continue to shrink, re-creating what you just sanded level.  This is more true on grainier woods than maple, but it does happen on maple to some degree.

If you properly fill and seal the wood, you'll have only one thing to sand level - "orange peel" - which is the texture created by spraying.  If you dont properly level the wood and seal it, you'll have lacquer going into grain, and it will take MANY coats, drying time, and sanding back to fill.  In essence, you'll be using lacquer as filler, and this will take FOREVER to dry well.

As you apply more lacquer, you'll be re-wetting the lacquer under it.  This will re-swell that lacquer to some degree and also increase drying times.  Also, if you respray too soon, you'll trap solvents that will have to slowly migrate through the layers above where they're trapped.

All this means - you need adequate drying time, the right lacquer, and the right technique. 

Lacquer can be very easy to use, if you're prep is good, your technique and materials are matched to the job, and you take enough time with things - especially preparation and drying time.

The same things that make lacquer easy make repair fairly easy too - as lacquer will remelt into itself, making repairs almost invisible.

 

[Jeremiah]

Thanks for the information CB, it's really helpful.

Would I be right in assuming that because the paint contains the same or similar solvents to the lacquer, it will also shrink as the solvent evaporates? (Is there a big difference between acrylic paint and acrylic lacquer other than that one is coloured and one is clear?)

Does the shrinking only matter on the lacquer because it's the final coat so it will be visible if it shrinks after the sanding?

 

[dmraco]

I agree with CB....to address DesmoDog..that two weeks takes into consideration I usually spray 2 base coats 3-6 color coats, and 6-8 clear. 

Like CB said it shrinks.  It is OK to sand after 24 hours but I feel better and have a better surface to work with at the 7-14 day mark.  I also spray a lot of heavy flake.  I have seen too many people rush to sand at 24 hours a screw up a great looking paint job.  But please do not wait longer...like I said...that stuff gets hard and will never polish well if it is eft to go longer.

 

[nestron3030]

so let it cure for two weeks exactly? or two weeks minimum? what would be Maximum curing time?

 

[dmraco]

so let it cure for two weeks exactly? or two weeks minimum? what would be Maximum curing time?

like stated before, it can be sanded as early as 24 hours. 

***My personal preference, and what has worked well for me on motorcycle parts, especially when spraying MULTIPLE coats, it is let it dry and set up for a week.  I would NOT let it sit longer than two weeks because it becomes too hard.  I would say 7-10 days if the sweet spot.

If you are simply spraying 2-3 coat of clear over a dyed, stained, previously painted body, 2-3 days sould be fine.

 

[-CB-]

so let it cure for two weeks exactly? or two weeks minimum? what would be Maximum curing time?

There is no answer to that.  It depends on your materials, and the environment, and your technique.  THICK lacquer takes forever to dry - literally forever, it may never ever get fully cured.  Some materials take forever to dry too, they're made for thin application on things other than guitars. 

You've not included enough information to get even a hint at what you're about to do..... so I'm afraid I gotta be roundabout with the answers.

Sanding orange peel off after 24 hours - may work, may not. 

=AND=

Quit being in a rush.  Patience is a virtue, and more so in lacquer.  Let it cure, give it the time it needs.