Finish Blotches on new makers' instruments

[SnowManSnow]

I've started finishing my instrument with ACE varnish, see other thread. When I applied the first coat I noticed there were spots where the varnish didn't look like it stuck... Kinda finger print looking spots (which it VERY well could be). At that point I realize it is what it is.. and press on with my very first build..

That being said.. i just saw another person's build with the SAME kind of spots.

What causes this? is it glue? is it where the pore fill didn't hit? (possibly sanded through to the wood):?

Any insight would help me greatly on my next build (which I believe will be another kit... in which I'll try and incrementally build my skills and cut down on the errors I made this time).

Thanks.
B. Snow

[joinercape]

Could be glue, possibly oil spot from skin, etc. When the instrument is raw, be very careful handling it, I usually did a wash coat of shellac right away once the sanding/scraping was done. Live and learn, your instruments and your technique will improve with every instrument you build.

[SnowManSnow]

Originally Posted by joinercape

Could be glue, possibly oil spot from skin, etc. When the instrument is raw, be very careful handling it, I usually did a wash coat of shellac right away once the sanding/scraping was done. Live and learn, your instruments and your technique will improve with every instrument you build.

so just a wipe on coat ?

[charles Tauber]

A photo is necessary to better understand the issue.

One potential issue with a wash coat of shellac is that it isn't "water white" and will color the wood. If you don't want the wood colored, that might not be the option you want. Test on scrap.

[joinercape]

Originally Posted by SnowManSnow

so just a wipe on coat ?

Everyone has their own method, but I preferred wiping on a 5/1 cut of shellac, using a clean fod or pad (no oil). It will soak in fast so you have to keep moving, starting and ending off the work. Notice I said wipe on rather than rub in, the rubbing comes later. Shellac is a very good undercoat/sealer for lacquer or oil finishes, as well as a base for French polishing, which is usually shellac and oil (I like walnut oil), though really describes the technique rather than the material. Be careful over dark resiny woods like rosewood, the color can run, you may want to wash the rosewood with solvent and let it dry completely before sealing. As mentioned above its always a good idea to practice on scrap woods, so you get the feel for it. And yes, anything you put on wood will color it to some degree, and even the most blonde shellac has some color.

[Truckjohn]

What thinner are you using? You have to use the right stuff or you get a gooey, sticky, blotchy mess. VM&P Naptha or stinky Mineral spirits are your best choices for oil varnish. Squeaky new fresh Denatured alcohol for spirit varnish. No acetone, lacquer thinner, kerosene, or odorless mineral spirits....

Last thing is surface prep. Don't sand too fine - 220 is good for the wood under brushed varnish. Then - do your surface prep immediately before brushing. You can't sand then paint 2 weeks later... You brush as soon as you finish sanding and give it a good wipe down with a clean, dry lint free cloth. I like good quality paper towels to wipe down with because I am not tempted to reuse it without a good washing.

I did shellac once under varnish... Complete catastrophe. Shellac is alcohol base where varnish is oil base... I ended up with the varnish peeling off in sections... The varnish dried and cured just fine - just didn't stick in certain sections... Never again. Instead, I use a heavily thinned wash coat of varnish to seal and raise the grain... Full can strength varnish for a seal coat was also a catastrophe... It went on thick and gloppy in sections and thin in others. Raised grain caught big blobs of varnish and make a dark, ugly, puckered spot that never really cures... The solution to this is to scrape off the goo, sand back, and then apply a properly thinned coat.

Thanks

[Bruce Sexauer]

I see you did not take my advice about doing a finish on something else first.

It is quite important in most cases to have an even (or at least complete) coating of sealer before starting the varnish itself. The sealer of record in my method can be coated directly OVER the varnish in the event a that there is trouble such as you describe, but make sure you have deglossed the varnish.

Shellac is a wonderful sealer, but some shellac has wax in it, and that must be avoided as it inhibits rather than promoting to bonding of the varnish causing the kind of problems truckjohn describes. Also, I use turpentine and acetone to thin my varnish, never generic thinners as their formulation varies considerably as do the results they obtain. Even at that, there are thinks called turpentine that are not, and the piney smell (the force, Luke) must be strong.

[SnowManSnow]

Originally Posted by Bruce Sexauer

I see you did not take my advice about doing a finish on something else first.

It is quite important in most cases to have an even (or at least complete) coating of sealer before starting the varnish itself. The sealer of record in my method can be coated directly OVER the varnish in the event a that there is trouble such as you describe, but make sure you have deglossed the varnish.

Shellac is a wonderful sealer, but some shellac has wax in it, and that must be avoided as it inhibits rather than promoting to bonding of the varnish causing the kind of problems truckjohn describes. Also, I use turpentine and acetone to thin my varnish, never generic thinners as their formulation varies considerably as do the results they obtain. Even at that, there are thinks called turpentine that are not, and the piney smell (the force, Luke) must be strong.

I did "finish" some scraps to try and get a bit of the technique down, and they were fine.. at least as far as laying the coat in.
The issue is that something was ON the guitar that I couldn't see until the finish was applied, or at least I didn't realize what to look for perhaps. Once I put the finish down it popped.. As I say, i didn't notice anything upon inspecting it BEFORE putting down the varnish. I also applied the pore filler, and it appeared fine. That being said i DO think i may have sanded through the filler in a few small places. Its just not something I had a feel for yet.

All this into consideration I'm still enjoying whats going on. Hey, its a first guitar, from a Martin kit, (which I probably wouldn't try again... just not impressed with the kit wood / other materials at all).
At the end of the day I'll have a guitar that I poured months of my attention into that I learned a great deal through.

B

[Truckjohn]

Can you post some pix of the "bad spots". They seriously sound to me like they are thick blobby spots or a run in the varnish that puckered. Those are actually pretty easy to deal with and to prevent with technique and brush choice - but what you do to fix it depends on how thick and gloppy it is in those places.

Thanks

[Frank Ford]

The bad news is that it takes practice.

Same as playing guitar, you gotta practice, you know like, "forever," to be a good musician. Well, the same thing applies to woodwork and so many other crafts.

As much as we'd like to have it handed to us digitally or verbally, it just doesn't work that way. To get really good at finishing you have to make half a lifetime's worth of mistakes until you really have a handle on things. Finish can be the single most troublesome part of any guitar factory process.

[Halcyon/Tinker]

Amen.

.........

[Bruce Sexauer]

The reason I said that you didn't take my advice is that getting a proper guitar finish surface is not a day or two's work. The pore-filler alone is usually overnight at least. Varnish goes on one coat a day, fully sanded between each coat, and my best time ever was 6 coats, so 7 days. Then it should cure before finessing the surface prior to buffing, and that is a least 3 days, and ideally more like 3 weeks. You don't really find out too much about how your application went until you sand the gloss off. That is educational.

Sanding through the pore filler is surprising as it is not on the surface, it goes in as far as the pores are deep. Also, I do not actually sand the porefiller, I use a coarse cloth to remove the excess. A 600 grit sanding sponge (Norton soft-touch) will do a great job removing ny haze, but never sees the wood because like nearly everyone, I seal before the porefiller goes on.

[SnowManSnow]

So when you do sand the varnish before the next coat you said "fully sanded"... To what extent are you sanding? Are you really getting down on it? Or just really scuffing it for the next coat? Sorry for all the questions... Just learning as I go.


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[Truckjohn]

Just scuffing for the next coat and knocking down runs/blobs that will give you hang later.

[Bruce Sexauer]

I use 320 soft touch for the first 2 coats as it knocks the tops of the texture off and also scratchs into the valleys some. The following coat of varnish will not stick to the gloss of the previous coat. On the third coat I get more aggressive and use 320 paper on a hard block (repurposed flip flop sandal is great) and actually flatten the surface to a round 80% glossless before pulling out the soft touch again to get into the valleys. Coat five should get nearly perfectly flat, and any serious discrepancies should be drop filled. I switch to 600 soft touch around this point in finessing the hardblocks discrepancies.it is EXTREMELY important to error on the side of caution in all stages, for you NEVER want to sand through to wood. if you do so, you must reseal. Once the entire surface can be perfectly flattened, the following coat can be wetsanded using nothing coarser that 1000 grit, this is what I call the penultimate (next to last) coat. The final coat should be left to dry for no less than 3 days, but ideally 3 weeks. Then sanded with 2000 grit using the previously described hardblock until there is again no gloss or texture whatsoever. Then buff. This process represents over twenty hours per guitar of my time, and your mileage may vary considerably.