Top finishing question

[Paul Eisenbrey]

Hi all,

So far the finishes on my builds have ranged from dreadful to tolerably bad. Finding out about ZPoxy has helped tremendously on the backs and sides of the last couple of guitars, but my tops are still unacceptable. It seems that no matter how carefully I sand the spruce, I cannot get a smooth finish on the tops. You have all probably seen this problem: areas where the wood is missing between the grain lines, giving parts of the top a kind of washboard look.

Does anyone use a pore filler on the tops to fill in these types of areas? Or do you just keep piling layers of finish on the top until the finish fills them? Or do I just need to cultivate patience and keep sanding?

Thanks!

--Paul

[deadedith]

Try sanding across the grain on softwood tops. Sanding with the grain sands the softer grain lines down more quickly than the harder grain lines they alternate with, so you get the washboard effect.
A random orbit sander works okay, but imho not as well as cross-grain sanding.

[Trevor Gore]

You have all probably seen this problem: areas where the wood is missing between the grain lines, giving parts of the top a kind of washboard look.

One has to ask why the wood is missing. Torn out through planing the wrong way? Scoured out with too coarse a grade of paper? Eroded out by continually using too fine a grade of paper and not knocking down the hard grain?

One fix that is pretty hard to get wrong is to plane the right way to thickness, clean up with 180 grit, inline, carefully on a hard cork block, finish up using 220, 320 and 400 on a good quality random orbital palm sander (orbit 3mm or smaller). Metabo (amongst others) make a good one. You should have a shine on the wood you can see you face in (and no corduroy).

[Allen]

Many people starting out will think that a finish on a top should be as dead flat and shiny and a new Mercedes, 'cause that's what they see hanging on the wall in the music shops. While it's quite possible to do that by piling on a catalysed finish like the polyesters that most factory guitars use today, it's not what I think most hand builders would be wanting to do.

I've had to do some repairs to guitars that have had a poly finish on them that was 2mm thick. I kid you not! That would be about 2/3rds extra thickness to most guitars and more than double of a ukulele top. Sure they were dead flat and as shiny as a new penny, but they sounded like crap.

Oh, and I would never in a million years use anything like a epoxy to level a soft wood top. They don't have pores, so what would you be trying to do? It's all about the preperation. Get the foundation right and everything else comes easy.

Trevor's comments about getting the wood smooth are part and parcel of this. Many people go straight to far too fine a grit from the get go. Not realising that fine grits only refine what was there previously. They DO NOT level anything. So you will undermine the softer summer growth wood and not touch the harder winter growth.

You should be aware though that when you do a fine and thin finish, even with the wood perfectly flat to start with, you will end up seeing the grain lines. First off the heat from buffing may show this up, but fluctuations in temperature and humidity surely will cause this. I look forward to seeing this, as it's a sign that the finish is just thick enough for the gloss and provide the protection, but not thick, heavy and sound dampening.

[kiwigeo]

You should be aware though that when you do a fine and thin finish, even with the wood perfectly flat to start with, you will end up seeing the grain lines. First off the heat from buffing may show this up, but fluctuations in temperature and humidity surely will cause this. I look forward to seeing this, as it's a sign that the finish is just thick enough for the gloss and provide the protection, but not thick, heavy and sound dampening.

+1.

[Bob Connor]

+2

[Kim]

=3

[Kim]

[Trevor Gore]

Pure genius!

You guys must all be as good at maths as Martin!

[simso]

Lacquering is an art.

First dont bother trying to pore fill spruce, its just not necessary.

Most people that I see that fail at finishes, only happen because they rush the job, or they think it can be done in one hit.

For a smooth finish, you must build it up in layers and sand between the layers, the final coat gets wet sanded and then buffed to perfection. Dont be surprised if you do 10-20 coats over many days, after all the sanding and buffing you will probably only have the equivelant of three coats thickness

[Paul Eisenbrey]

Wow, you guys really are math wizards!

Comparing my current technique to the responses on this topic, I can see several things I've been doing wrong. Most notably: I never, ever sand cross-grain. Probably something my Dad taught me when I was 5 or something. I've never questioned that advice, but it sounds like that is what is biting me the hardest here.

Should I go cross-grain on all grits? And, how far should I go with the sandpaper? I've had good results on my necks sanding all the way through to micromesh before finishing.

BTW: I absolutely agree about the awful 'dipped in plastic' finishes I see at the stores. I prefer a satin finish myself, and as thin as I can get away with. Hard to imagine that you could ever sell something with a 2mm thick finish. It would sound like a brick, I think.

Thanks again guys, this is great advice!

--Paul

[deadedith]

My $.02 (U.S. ) - cross grain up to 220, then a ROS with 220 or 320, good to go. If you are finishing with tru-oil, you can micro mesh all the way to 12000.
I'm way over here where you can't get to me if there is a problem, though, so be sure to listen to the guys close to you where you can exact revenge if the advice isn't good!

Seriously, the above method has worked well for me, but I have no problem if someone disagrees. We're all in it together.

[Allen]

That old advice about never sanding cross grain comes from a time when a fine sanding for many home handymen was about P80 grit. Still is I think for some.

I never go across the grain with anything coarser than P180. It will put in scratches that are a complete pain to get rid of.

If I'm finishing with lacquer, as most of my work is, I never sand finer than P400 on soft wood. P320 on hardwoods. Any finer and your just waisting your time and material.

I thin my lacquer so it's 50/50 but if you aren't using the same product this will mean nothing.

My finishing schedule has evolved a bit over the last year. Now I put down 2-3 coats of lacquer the first day. Let it dry over night to a week, depends on how busy I am. Rub back with P400 dry so I can see any shiny bits that may still be low. Spray 2-3 more coats over the day and let dry again for a day to a week. Then wet sand with P800 until the surface is perfect. Spray 2 more coats and let dry for at least a week.

This finish right off the gun is better than most you will see on factory instruments. But I still give it a light sand with P1200 wet and then a buff. Very high gloss but very thin finish.

[kiwinoz62]

Hi everyone,

Paul, great topic, lots of interesting discussion.
I'm in the middle of finishing my #2 build and seem to have run into the same problem as you (washboard effect).

Steve as you said, I think we all try to achieve a finish in one hit, only to find when we begin the buffing process, hidden mistakes begin to appear
Allen & Steve your advice to build the layers of finish is great and is something I will be following in the future.

I use Durobond as a finish & I'm happy with it, but I know next time it will be a whole lot better after this discussion.

[Jeremy D]

Man I wish this thread had of been about a week earlier. I have a similar effect on mine. I sprayed the first coats on the weekend. Its not so bad though. The worst part is i put a sponge in the sound hole to protect the inside and it must have been dirty. There are red dust marks on the top under the lacquer. Oh well looks like this instrument is having a pick guard .

[Phil Mailloux]

Allen, that sounds like a very thin finish, what do you use for product?

I use Mirotone NC on my electrics and usually spray about 15-20 coats thinned 30%, sounds like I might have to go way thinner for acoustics

[kiwigeo]

Some people sand the cr*p out of Englemann and other furry top woods and find they still cant get rid of the nibs. Try stiffenin up the nibs with a coat of egg whites and then knock them off with a sanding session. If there are still nibs then repeat.

[deadedith]

Timely advice, Martin, as I was just looking at a very nibby piece of Engelmann and wondering about it. I'll try the egg whites.
Thanks.

[simso]

If your painting the top, avoid things like sponges in your sound hole, get a small party balloon and inflate it in there, works an aboslute treat.

[Clancy]

get a small party balloon and inflate it in there

That's what I do whenever I spray a finish - even works for 'f' holes.

Incidently, I 'discovered' the washboard effect when I first stared using shellac.
I thought I had a problem, turns out I didn't. Done 12 instruments this way now.
viewtopic.php?f=1&t=3013

[simso]

Speak of the devil, one of my guys had to paint a top today, but he was rubbing the balloon a bit too much me thinks.

[Allen]

Allen, that sounds like a very thin finish, what do you use for product?

I use Mirotone NC on my electrics and usually spray about 15-20 coats thinned 30%, sounds like I might have to go way thinner for acoustics

I use Mirotone 3220. And yes it's a very thin finish. Finishes on electric guitars come from a time when hot rods were the rage, and it seemed to be a badge of honour to say that your car had 50 or more layers of "hand rubbed" lacquer on them. They were using the paint as a filler and leveller to achieve a smooth mirror like finish. Never a good idea for all kinds of reasons.

With a well executed French Polish on an instrument the finish is whisper thin, and there is no reason in the world that you can't do the same with a lacquer finish. It all comes down to prep. But you only have to read through a forum for a few days to find out that the vast majority of people absolutely hate sanding and are looking for the "easy way to a fabulous finish".

All sorts of things can and will go wrong with a lacquer finish that is applied too thick. All are part of the ageing process that can't be avoided. The most common and obvious one that you would be aware of is checking of the finish. The cracks you see that are associated with thermal shock among other things, but's it's the thickness of the finish that is the main cause.

Most people aren't aware that nitro based finished never stop drying out and shrinking back. There is the initial quick phase where the majority of the solvent's gas off over the first month or two, but the process continues albeit at a slower rate until the finish is well...finished. Life span on lacquer is approximately 75 years if you did everything right and proper care was taken during this time.

[Nick]

Speak of the devil, one of my guys had to paint a top today, but he was rubbing the balloon a bit too much me thinks.

Classic Steve
I use the ballon method after seeing Bob Benedetto shoving them in his F holes ( ) & I'm in Allens camp, I'd rather see a slight washboard effect on my tops than a perfectly smooth finish, I use two pot Urethane so don't get quite as much 'shrinkage' as a solvent based finish but it's still a good indication of 'just the right amount' when I do see a slight instance of Spruce grain ridges.

[Paul Eisenbrey]

So, let me get this straight....

1) I've been sanding all wrong. (BTW, I actually like sanding -- I find it calming in kind of a zen way)
2) Even if I do the sanding right, the grain should still be apparent, or I've messed up the finish work, and
3) Rub soundhole balloons in private.

That about cover it?

-- Paul