finishing question

[scuffle]

hey everyone,

im hoping someone can help me out. I have just wet sanded my laquer with 1500 grit but i have sanded through to wood. I figure i will just spray a couple of more coats to cover the through areas but I am wondering do i need to rough up the laquer on the guitar for the new stuff to stick? I am using mirotone 3220 and i know it burns in quite well but I wanted to be sure it would work before i started spraying

All help greatly appreciated

[Lutherie Gervais]

For what I know, I would refinish.
Even though it burns in quite well, it is going to leave a spot mark, It may work okay, but you might not be able to completly erase that spot you went through.
And you need a good scuff of 320 to allow lacquer to bond well.

Honestly, finishing job is hard to master, and if I were you, I would scrape back to wood, resand 320 and refinish the whole face of the area you went through. If your back and top are okay, and it's your sides the problem, redo the sides, or if it's only the back, redo the back, mask the rest of the guitar against the overspray.
And maybe shoot few layer more you have done ... We sure want the least amount of lacquer on, but honestly I really think we are being crazy about having less than 0.010", go on and spray some, make yourself the leveling process an easy and fun task, not worrying anymore, take extra time for a perfect surface.

That is my best advice, and I can guaranty you, you won't regret. Don't forget you can burn through at the buffing part also, take the time and it will make you some practice.

No need to rush, right !

[ozwood]

Hi Scuffle,


(Assuming you have not grain filled with Epoxy.)

IMHO , just wipe it over with some shellite , let it dry out for a few hours and keep applying light coats to the rub through area till you back a film thickness matching the rest of the instrument. then continue coating the entire instrument.

3220 has a really good burn in , you could re apply, (if you wanted) 5 days later without even sanding and still get excellent adhesion.

I would not recommend it , but you could.

I spray more instruments than I'd like too, and a rub through is not unheard of , that's all I do if it happens , never had an prob's.

Hopefully Allen will chime in and give his opinion.

Cheers,

[Allen]

You must abrade Mirotone 3220 if it has cured overnight. It's a precatalyzed finish. It will not burn in enough to provide a good and reliable bond.

No need to go coarser than P400 dry. If your finish is already pretty good, then you can go as fine as P800 wet, but not finer. You will loose any mechanical adhesion that you are trying to achieve.

It really depends on where the sand through is if you can just spot it in.

For instance, just on the edge of a binding....well then yes you could spot it in, and most likely I would go with that option if it was just one small spot.

If on a flat, then the very least you need to do is finish that plane. Like the entire top or back or what have you. Otherwise you will most certainly be able to see the blend, as the new lacquer will end up shrinking back and that blend line will show sooner or later. Most likely when you are trying to buff both up to the same gloss, or a few months later on.

There is a trick to how you mask so you don't get an edge when you do this, and it's something we do every day when spraying automobiles, but pretty difficult to explain. If you are unsure how to do this, then I'd suggest spraying the entire instrument.

You are going to need to get some lacquer on the bare spot without getting excess build up on the rest of the instrument. So you spot in those areas that require it with a few coats to get some build. Then apply more to the rest of the face or entire instrument. Whichever you choose to go with.

[scuffle]

awesome great advice guys! like i said all help is greatly appreciated

the laquer has cured for about 4 weeks before i sanded it back as (i thought) this was the last coat. does the cure time matter?

[Allen]

No. Just go with what I said before.

[scuffle]

awesome
thanks!

[ozwood]

Thanks Allan,

I have learnt something as we'll.

Cheers,

[Kamusur]

Like Paul said, we always learn stuff here. Good tips Allen ty.

Steve

[nnickusa]

As long as we're talking Mirotone, I have a question, if I may.

Why lay down 4-5 coats and then wait a week, sand and spray all the final coats? If it burns in as well as claimed, couldn't one just spray 10 coats on day one., wait a few weeks, buff and be done?

[Allen]

It comes down to getting those solvents out of the matrix Nick. What's in the first layer has to get out sooner or later. But one thing is certain. It's going to get out eventually.

Problem with putting too many coats on at one time is that the last layer hardens up and traps solvents in the lower layers. Good way to test for this will be to do as you suggest, and then in one week sand the surface. Put your nose next to the surface and if you can detect any solvent smell, then it aint dry yet.

You will not get as high a gloss as possible until that happens. As well you can level it out and buff it to an acceptable shine, but as the solvents continue to evaporate what appeared as flat and smooth will end up shrinking on you and leave a less than ideal surface finish.