Official Luthiers Forum!

Enclosed is a photograph of what I assume are witness lines where I sanded through the topcoats(Stew-Mac waterbase lacquer) to the sealer coats.  If you agree this is the case, I am wondering what I should do to correct the situation.

1. Must I sand with 320 grit ( or would 1200-2000 grit be OK?) to get good adhesion in this area and then spray several ( how many would you suggest?) layers of waterbase topcoat?

2. Can I just spray the immediate area of the witness lines or do I have to spray the entire neck with the new topcoats?

3. Would it be possible to French Polish over the witness lines to correct?

Any thoughts/help would be appreciated.

 

Bill

Good question Bill.  Welcome to the OLF.  Someone will be along with an answer, whether you like it or not.  The answer that is.  

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Bill, I spray Nitrocellulose lacquer. Each successive coat burns into the previous coats, so there are no witness lines unless you use coats of Epoxy fill, which you can sand through, causing a similar problem.

I really don't see a way to fix your problem without stripping or sanding back. Probably not what you wanted to hear.

Welcome to the OLF.

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http://www.dickeyguitars.com

My nasty comment about waterbased lacquers is that the main ingredient is wishful thinking. I read more problem posts about these finishes than about any other materials.

I use catalyzed (not UV cured) polyester, and I love the stuff.

Nitro lacquer is not all that hard to shoot, and the results are very predictable. It's not even that hard to rig up an impromptu spray booth with an explosion-proof fan. You should have that even if you're going to spray water based lacquer.

For low tech finishes, you might consider varnish or French polish. They each have a different look, but are just beautiful. Check out Bruce Sexauer's work in varnish some time.

  "wishful thinking"  ha ha. thats funny.

_________________
sweat the small stuff.

The colortone waterbased lacquer is Target coatings USL under the Stewmac / Colortone label.  I use it all the time and it burns in well. (Trust me, with my sanding technique, I have had plenty of chances to test it's burn in ability! )  I would scuff sand the area with 400 grit and lightly spray coats over the area.  Since the area is on the peghead, I would just spray over the entire peghead stopping at the neck.  Make sure to allow plenty of time for it to dry between coats.  I wait a minimum of 3 weeks before doing any final sanding or polishing as it is just too soft to work before that.

Good luck!

Three weeks...I'd go broke doing that!

I can rub out polyester in 24 hours if need be, and 48 hours is the standard cure time in our shop. Longer is fine but not needed.

I know that some folks seem to get decent results with waterborn lacquers, but the horror shows I've seen have kept me from being interested beyond my disastrous experiments several years ago.

Here's the other one I say, "When Bob Taylor switches to water based finishes, I'll do it, too."   

O.K. Rick...so please tell me/us what is involved with the finish you use....How do you do it? Dangers..etc...

Thanks,
Greg

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Gwaltney Guitars

Rick, How are you folks (both large and small) getting away with urethanes and polys? I know CA. is really pushing the waterbase finishes in automotive applications. Are you able to stay below the radar by not producing a high level of VOC's? I know Taylor has recently (within the last year) implemented a way to "electrify" the guitar body in such a way that they get a very high transfer rate with their UV stuff (think powder coat) I see a lot of trade mags (automotive) really pushing the waterborne stuff and from the limited experience I have had with it, it's a small nightmare. 

Well, I'm not below the radar. I have a fully legal spray booth inspected by the building department, the fire department, and the local air pollution control board, and it's licensed by the planning department. We can shoot anything we want here, and we wouldn't pop up a level in bureaucracy unless we went to about five times the number of instruments through here...and that we couldn't handle.

Addam Stark shoots nitro here, but everything I do is with urethane sealers or satins and polyester topcoats all of which are much lower in VOCs than nitro.   

Taylor's system is no powder coating. They use a Ransburg electrostatic attraction system whereby a coating of electrically conductive stuff is shot on first...I suspect it's pretty high resistance, but conductive enough...and then the piece is charged with several thousand volts of DC and the spray head is charged with the opposite polarity.   The liquid finish is attracted to the work piece and will actually wrap around. They've used these systems in industrial applications for several decades, but the problem has been getting this to work on clear finishes on guitar finishes where the quality has to be at the very top of what is possible. In the furniture industry the very finest finish is known colloquially as a piano finish. I wish we could get away with a piano finish!

The whole issue in industrial coatings comes down to cure time, and you're just not going to beat UV with any kind of evaporative cure whether it's water or anything else. Next to UV come the catalyzed finishes with low VOCs like I use.

Also the amount of finish shot in a small production shop like mine is nothing like what the average auto body shop shoots. Just think of the surface area of a bunch of guitars vs. a car. No contest. Our Monterey Bay Air Pollution Control inspector tells me that we aren't even a blip on the screen.   That doesn't mean we didn't have to jump through all the hoops, though...

Sorry to hijack the thread Bill!  Rick, didn't mean to suggest that you weren't legal. I am just curious about how CA. is regulating spray shops and just how hard they are pushing to get everyone on the waterborne stuff. It seems that higher regulations on pollutants seem to start in CA. and work their way eastward. Glad to know that you are still able to use the more user friendly polys and urethanes. Sometimes it helps when you don't create a lot of VOC's huh? I prefer cat finishes as well. I am intrigued by the UV stuff and spoke to Tom Anderson a short time back about how he has converted to UV. The actual UV material suppliers (finish) are rather tight lipped about their products while any Jo-Blo can purchase a UV lamp.

Bill, You could post your question at targetcoatings.com. They have a forum and a target person can provide answers.

_________________
A higher purpose for wood.
Rich Smith
Issaquah, WA

There are specific wave lengths of UV that do the curing, and anyone can buy the finishes if you know where to go. Don't think there's some kind of conspiracy to keep you out of the club. However, you do have to be ready to buy into the whole UV thing, and it's not cheap, and you have to be ready to buy at least five gallons of the UV cure finish to get any at all.   Also the finish companies don't have all the answers like you'd think they do. Tom Anderson uses finishing materials from five different companies. I use materials from four or five. We all make it up as we go along, and the finish companies are fascinated by what we come up with. In a real sense, we know more than they do about how to use their products.

Tom and Bob Taylor were incredibly helpful to me when I made the move over to catalyzed finishes, and now I've gone quite a bit beyond where they pointed me to with it all.

For instance, most of my sunbursts are now done with MEK soluble stains sprayed directly on the wood much like the Gibson 'bursts of the teens and Loar era. Then I brush on a couple of coats of Waterlox tung oil varnish, then McFadden rosewood sealer and then polyester. The look spans nearly a hundred years of lutherie with very hand done looking stained bursts and then the toughness and gloss of a thin clear poly on top of that.

Okay, at the risk of really sounding stupid here, I keep reading poly and polyester finishes but I don't know what they are.  I know all the other typical finishes and have tried some, but 'poly' is a generic term that doesn't help when I go to look for it.  What names might I know that are polyester (non-UV cure) that a amateur could get.  I would love to try it but I don't know what to look for or where to get them.  Could you tell me some brand names so I have a place to start?

TIA for answering this elemetary question!

[QUOTE=davidmor]The colortone waterbased lacquer is Target coatings USL under the Stewmac / Colortone label.  [/QUOTE]

Actually, it's not.

I contacted Stewmac a year ago & they said that "While the lacquer is a Target product, it is not the Oxford Ultima. It is made specifically for us to our formulation."

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Dave
Milton, ON

Out of respect to Bill, I think (I) we should take the clearcoat polyester/urethane/UV discussion to a thread of it's own. I, myself feel responsible for taking this discussion it the wrong direction. Sorry Bill. 

Now then, getting back to your initial questions. Yes, it looks like you may have sanded through your clear into the sealer. Witness lines are more of an issue when attempting to "burn in" "melt in" or "blend" into existing clearcoat with the same product or another product. There are so many variables involved in getting clear to blend into other clear and I feel it would be best if you just allow the finish to fully cure, then re-clear the whole neck. Its a small area and why risk another issue? (a failed burn in) If it were the top of the guitar, then we would be dealing with film thickness and attempting a burn in might be more appropriate. Understand that in order to burn or melt clear into an existing finish, it is very important that the clear be thoroughly dry. If you keep putting more and more material over uncured finish you can potentially trap solvents that need to flash off or "off gas" and this can lead to a whole bunch of other exciting failures. 

As Rick stated in an earlier post, seasoned pro's will encounter problems often when dealing with products that are all affected by temp, humidity, air line pressure and temp, flashing times, solvent/clear ratios and viscosity. heck, barametric pressure can even affect some finishes! there are a lot of things that can just simply go wrong. Bottom line is, you might not want to but you can always strip a finish and start over. Persistance will eventually lead to your own process and understanding of the product you use. It is not unusual to use a product entirely opposite from what the supplier suggests (As Rick also stated above) The trick is to find what works for you. Sorry to be windy.

[QUOTE=Dave Stewart]

[QUOTE=davidmor]The colortone waterbased
lacquer is Target coatings USL under the Stewmac / Colortone label.E [/
QUOTE]

Actually, it's not.

I contacted Stewmac a year ago & they said that "While the lacquer is a
Target product, it is not the Oxford Ultima. It is made specifically for us
to our formulation."

[/QUOTE]

Dave. I just contacted Target Coatings a month ago, and Jeff confirmed
that it is the same product. They just re-label it for stewmac. You can
use them together.

_________________
Mike

"The Dude abides. I don't know about you but I take comfort in that. It's good knowin' he's out there. The Dude. Takin' 'er easy for all us sinners. Shoosh." The Stranger

Seems odd that you would sand through the top coat to the sealer because, if I recall, you put on six coats of topcoat before doing a sanding.

_________________
A higher purpose for wood.
Rich Smith
Issaquah, WA

David, you might try
here for some
"poly" coatings. There are polyesters and polyurethanes, and they're very
different. I've used Ilva's polyurethane a few times, and I like it, although
it's not ideal for me. This place sells it in as little as quart quantities, so I
would assume there's a chance that they might sell their polyester in
small quantities too. I haven't tried that though. M.L. Campbell makes
another polyurethane that I've used, but I don't think they make a
polyester.

I would just recommend learning about the safety hazards of these (and
all) types of finishes before using. You don't want to use them without a
spray booth and all the right gear.

_________________
Mike

"The Dude abides. I don't know about you but I take comfort in that. It's good knowin' he's out there. The Dude. Takin' 'er easy for all us sinners. Shoosh." The Stranger

Bill, I recently got what I thought were witness lines with USL, but I think it
has something to do with rubbing out the finish using water. If I use
abralon pads without water, I don't get the "lines." Yours looks quite a bit
different though, more like the layers didn't adhere and actually
separated in the middle??? Or maybe just real witness lines.

You might give dry sanding a shot though before sanding back and
spraying more. Abralon pads can be found at some auto paint stores. I
have been using 1000-4000 grits.

_________________
Mike

"The Dude abides. I don't know about you but I take comfort in that. It's good knowin' he's out there. The Dude. Takin' 'er easy for all us sinners. Shoosh." The Stranger

The most common cause of sand through, which is what you show in the picture,(not witness lines) is sanding with out a back-up pad and trying to sand too quick and aggressively. Remember we are trying to form a level surface without sand off any more film than required to achieve the level surface.

It really does not mater if the finish is waterborne, nitro, or whatever. You need to clean off often and check for sand through. Soon as you see a sand through start, STOP don't sand in that area any more. This should leave you with only a small opening in the film.1/4" diameter or less. Finish sanding everywhere you can with out going through. Clean up, then respray those areas that need touch up with 2-3 more coats. With USL you could allow a week before leveling those areas out and you should be good to go.

Remember to use a backing block and light touch and you will have a lot less of these.

Be sure to clean up the sand through well. You do not want to leave any finish dust at all in the boundary of the sand through or anywhere else for that mater. Or you will end up with witness lines

Bill-did you clamp your headstock in a vise to rub out the rest of the neck?Looks like a clamp mark!
I've used Stew-macs H2O for years and have never had this problem!
How long did you wait before rub -out?
How many coats?

Yes you can respray JUST that area -make sure there is no polishing coumpound residue left!
Just ruff up the area with synthetic steel wool and re-spray!
Put on enough coats so you do NOT sand through again!


www.collinsguitars.com

_________________
Mike Collins

Thanks Ricardo, Joe, Mike, and Michael

Yes, I think I caused the witness lines by overzealous sanding of the area as I was trying to remove a "V" created in the back of the headstock by earlier sanding ( while still in the white) of the triangular pyramid ( I'm sure there's a better word for this) just below it. I didn't notice the lines until I applied the finish. I will chalk this up to being a newbie and not paying enough attention to the smoothness of the wood in the white. Oh well, I think I've just learned another lesson that will be hard to forget. But it's all about the journey, right?

Again, thanks so much and peace be with you.

Bill

Yep, been there & done that.  "In the white" sanding quality is the first key to a great finish.



I've been getting myself in the habit of finish sanding (dry) all the
way down to 1000 grit Abralon (or higher with harder woods) so that I
can find all these kind of imperfections and fix them before the finish
goes on.  Then I will go back over with 320 grit or 400 grit
before applying the first sealing layers.



I went straight from rattle can polyurethane to HVLP and pre-cat
conversion varnish, which I LOVE.  Dry to the touch in 10 minutes,
level sand it after 60-90 minutes.  But the fumes will kill you
faster than crack, so you need all the precautions.