Sand-through with water borne lacquer

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Sand-through with water borne lacquer

Postby Steve Sawyer » Mon Jan 22, 2018 11:17 pm

I have a test piece (see the pic below) that I'm using to learn some new techniques to use on the next build, including veneering, binding and finishing with water-borne lacquers (GF High Performance).

I'm really pleased with the HP overall - it's very hard and polishes real well. The trouble is, I sanded through in three spots and am concerned that I'm screwed. I applied 15 coats. I'd brush on three coats in quick succession - no more than 12 hours, and usually much less - then wet level-sand with 400. After the final three coats I let it cure for a few days, then began the final wet-sanding with 800 through 2000.

I'm guessing I should have used more coats given the sand-through problem, but I note that Mike Conner cites only 8 coats (with Enduro-Var) in his build logs, so I thought the 15 would be good.

My big question now is this - am I doomed, or can I apply some more finish and get back on track? My guess is "no" because unlike lacquer, my understanding is that this stuff won't cross-link between coats once it's cured fully. My understanding is that this is not an adhesion problem, but really bad witness lines between the coats laid down too infrequently to get some cross-linking of the finish between coats.

Thoughts?

Thanks!

Test Block Finish.JPG
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Re: Sand-through with water borne lacquer

Postby Gordon Bellerose » Mon Jan 22, 2018 11:54 pm

I have never brushed my water base lacquer, so I'm not sure I can help.
15 coats seems like a lot. Even spraying, I've never used more than 12.

One thing I can tell you is that I never wet sand in between coats; only dry sand every 3 coats, unless there is a run. Then I stop, let it dry overnight, sand and continue. Wet sanding only takes place once the final coats are applied and cured for 4-5 days, maybe more depending on your humidity levels.

I usually apply 3 coats per day maximum; at least one hour apart, but no more than 2 hours. Then dry sand lightly with 400 grit.

I think the imperfection you are seeing may be caused by water introduced while wet sanding.
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Re: Sand-through with water borne lacquer

Postby Brian Evans » Tue Jan 23, 2018 2:12 pm

Their instructions don't mention cross-linking or a re-coat time. They do say that you can top-coat almost any water based or solvent based finish with it, so I would scuff with 400 and put on another three coats and see what happens. They say it takes 28 days to fully dry, which again doesn't sound like a pre-catalyzed lacquer to me.

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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Tue Jan 23, 2018 3:31 pm

Thanks for the thoughts. I don't think that I'm getting an artifact of wet-sanding, Gordon. What you may be seeing is that being new to such highly-figured veneer, I inadvertently used too much glue which oozed up a lot through the veneer, and had to be sanded off. It looked pretty uniform after sanding and filling with epoxy, but as I sanded through I could see what looks suspiciously like veneer glue. Obviously, I'll be correcting this problem when I get to the actual guitar build.

Brian - I have nothing to lose, so I was planning on doing exactly what you suggest. All my previous wood finishing experience has been with wiping varnishes, so this is all new to me.

Here's another pic to get a better view of the bad spots.

Test Block Finish 2.JPG
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Re: Sand-through with water borne lacquer

Postby Gordon Bellerose » Tue Jan 23, 2018 5:02 pm

Looking at it from that angle, it sure looks like glue under the lacquer.
Having said that, you should have been able to spot that in the first couple of coats.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Tue Jan 23, 2018 5:48 pm

Gordon Bellerose wrote:Looking at it from that angle, it sure looks like glue under the lacquer.
Having said that, you should have been able to spot that in the first couple of coats.

Nope. That disappeared completely under the epoxy. Everything looked good until I got to the final sanding. Things started to go south when I got to the 1500 grit. Not to say what we're seeing there is NOT glue - I'm willing to bet it is, but again, I know how to correct that. I'm just trying to figure out how to avoid the sand-through.

I was really interested to see how things would look (despite the glue squeeze-through) after the wetting by the epoxy. I was most concerned about losing the chatoyance of that veneer, and was super amazed how good it looked. If the chatoyance was compromised, it was only slightly. Also, you can see the witness lines around that spot in the lower-left where it looks like I went through the lacquer into the epoxy.

Clearly, I made a lot of mistakes here, and am trying to determine if I've learned enough to correct all of them when I get to the actual build - or if I should simply go back to what I know and do a wipe-on (like maybe Tru-Oil). Since some are having good results with the water borne lacquer, I'd like to be able to keep this as a finishing option going forward. Part of that learning curve is to correct the sand-through screw-up. Maybe I was just too aggressive in the sanding, or didn't allow the finish to build enough. Given your experience with spraying, and Mike Conner's experience with brushing, it would seem that I should have had enough build. It could be too that I didn't do as good a job of level-sanding every three coats (more work with brushed vs sprayed), and was having to do too much in the final sanding to remove the tiny bright spots that remained.
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Re: Sand-through with water borne lacquer

Postby Mike Conner » Tue Jan 23, 2018 8:54 pm

Steve,
Based on my experience with waterborne EnduroVar, it could be the wet sanding contributed to "local" softening of the partially cured intermediate coats of finish. I've been essentially dry sanding, using a bowl of slightly soapy water to rinse off the dust from the sandpaper and a damp microfiber to wipe down between grits. I don't flood the surface for the intermediate leveling between sessions, and just maybe a little wet for the final sanding.

If you are getting the surface pretty wet maybe there is some chance you are introducing water back into the finish?

Also, 15 coats seems like a lot, but I suppose that depends on how thick your build was each layer. It does take time to cure for the final leveling, and the more finish you have on the longer time may be needed for all of the water to leave and achieve the full cure. The EnduroVar has a distinctive odor -not ammonia like water poly, or strong like an organic solvent, but kind of musky. I have a pretty intense sense of smell, and can actually track the progress of the cure by waiting for the odor to fade. For my schedule, this seems to be about 5 days for the initial leveling, and then another 5 days or more for the final level and polish.

Sand through is a risk for most everyone, and I've read where even experienced builders can have mishaps. Sure is nerve wracking when it happens. So far, as long as I didn't scrub into the dyed wood surface, the EnduroVar dropped fill or touched up OK. Also, I've had good look with superglue to drop fill small gaps at the binding.

Great move to experiment before commiting to the instrument - that's helped me build confidence too.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Tue Jan 23, 2018 9:49 pm

Mike - thanks so much for your input. I was wet-sanding with 400 after every three coats, and never felt that there seemed to be any issue with that. Also, the final (wet) sanding went just fine until I got to the 1500 grit. Up to that point everything looked super - a nice even matte surface on the finish. I was using Alan Carruth's technique of sanding in only one direction and rotating that 90* for every grit-change so I could make sure I was removing all of the scratches from the prior grit.

I'm assuming from your and Gordon's comments that these finishes don't load when sanded dry (which is why I was doing it wet) so I can certainly give that a try on the next go-'round. My sense of smell is terrible, so I can't use your technique for judging the state of the cure. I was trying to never exceed about 18 hours between any of the coats, and would give every 3rd coat at least four or five hours (typically overnight) before doing the level-sanding. Do you think that schedule was appropriate? I waited several days (three to the best of my recollection) before doing the final sanding, but from what you and Gordon are saying, that sounds like it was too soon and may have contributed to my problem.

Tomorrow I'm going to start re-applying finish and we'll see if I can recover. I'm going to be a little more strict about the schedule this time. I'll use Gordon's min 1 hour max 2 between coats, and do no more than three coats per day, allow to dry overnight, level-sand (dry) before applying the next three coats, then allow a full 5 days to cure before doing the final sanding. If successful, I'll have a lot more confidence using this on the actual build.

Thanks again for everyone's input and suggestions. We'll see how this goes...
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Re: Sand-through with water borne lacquer

Postby Barry Daniels » Tue Jan 23, 2018 9:51 pm

Sounds too me like you are over sanding. What different grits did you use after the final coat?
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Tue Jan 23, 2018 9:58 pm

Barry Daniels wrote:Sounds too me like you are over sanding. What different grits did you use after the final coat?

800, 1200, 1500, 2000
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Re: Sand-through with water borne lacquer

Postby Gordon Bellerose » Wed Jan 24, 2018 12:01 am

When I am dry sanding in between coats, I generally use 400 grit.
This is the next day, after the three coats from the day before have dried.

This sanding is not a heavy sanding; more of a scuff sand just to give the finish a bit of grit for the next coats to bite on, and look after any runs that you may have.
Watch the corners and edges. It is usually there that the sand throughs happen, because the finish doesn't build as fast in those areas.
More of a wipe than a sand in those areas.

Try not to lay the guitar flat while spraying / brushing and curing. Hanging it vertical is better. You are more prone to put too thick a coat on a guitar that is laid flat.
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Re: Sand-through with water borne lacquer

Postby Mike Conner » Wed Jan 24, 2018 7:32 am

Yep, what Gordon says tracks with what I do.

Not sure about GF you are using, but the EnduroVar sands to a nice talc-like powder and really doesn't load too bad. Rinsing the paper by dunking in a bowl of water keeps the paper fresher, and I pat dry on a paper towel before returning to sanding.

For me, it's 3 coats about 1 to 1.5 hrs apart, then cure overnight to 24 hrs.
As Gordon says, the 400 grit sand is to knock down higher spots or brush strokes, and take care of any runs. With dry sanding and light pressure you can see where the high spots are getting sanding, and I try not to sand past when everthing looks dull.

Repeat above - 3 coats, 24 hrs, 400 grit.

Then two final coats and 5 day cure to level sand to about 1200 grit.
Wait 5 more days, sand 1200, 1500, and 2000, then rub out.

Like Gordon cautions, be really careful near edges, that's where I struggle too.
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Re: Sand-through with water borne lacquer

Postby Barry Daniels » Wed Jan 24, 2018 11:26 am

One guide to sanding is watching the shiny spots (valleys) slowly disappear. You want this to happen as you work up in grits. If the valleys disappear with your first sanding of 800 grit paper, then you may not have enough film thickness to allow you to sand with the finer grits.

By the way, the only way to see the shiny valleys is to stop sanding, wipe up the residue and dry off the surface.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Wed Jan 24, 2018 2:44 pm

Mike - do you ever thin your finish? It seems that I have a lot more leveling to do with the brush marks (even with a foam brush).

Barry - interesting your comment "If the valleys disappear with your first sanding of 800 grit paper, then you may not have enough film thickness to allow you to sand with the finer grits." THAT alone may have been my problem. As I mention above, I have more leveling to do because I'm brushing, not spraying, but based on my one prior build using nitro, I was removing all shiny spots with the 800 before proceeding with the final sanding. I remember pausing, wondering if I should proceed with finer grits to finish the leveling, and decided that it seemed more correct to completely level with the 800.

I'll keep in mind that further leveling will continue with the finer grits, and not be so concerned if some shiny spots remain after leveling with the 800.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Wed Jan 24, 2018 2:50 pm

Mike Conner wrote:Like Gordon cautions, be really careful near edges, that's where I struggle too.

Yeah - Gordon gave me great advice on that with my prior build, and I had no problem with the edges. This one is a little different in that I have the binding to deal with, yielding a sharper edge (and thus more vulnerable to sand-through) and wanting to get a nice smooth transition from the veneer to the binding, but so far his advice to work up to, but never on the edge has worked well. As he put it "the edges kinda take care of themselves", and I'm finding that to be true.
I was sorta perversely pleased that my sand-throughs on this test block were NOT on the edges!! :D
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Re: Sand-through with water borne lacquer

Postby Barry Daniels » Wed Jan 24, 2018 4:28 pm

When deciding to move on to finer grits, keep in mind that they will be removing less material so don't leave deep valleys. But a few shallow shiny spots can be left to serve as indicators of how far to sand. If the last shiny spot disappears with the 2000 grit paper then you achieved the least amount of removal possible while still getting a completely level surface.

When I first started building I over-sanded everything. My first guitar had every wood surface inside and outside sanded though every grit available up to 600. As experience grew I learned that I could get away with much less sanding of both wood and finishes.
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Re: Sand-through with water borne lacquer

Postby Mike Conner » Wed Jan 24, 2018 7:49 pm

Steve,
I haven't thinned the finish to date. I'm willing to live with a few more evident brush marks because the application is so simple and uses the minimum amount of finish. I have a really good Turbinaire HVLP and have had good success with waterborne poly on furniture, but have so far not wanted to work through developing spraying procedures for EnduroVar.

While thinning with distilled water could conceivably slow the setting up and flowing out, it could also lead to more sags or runs.

I'm just continuing to work slowly and learn as I go.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Sun Jan 28, 2018 3:17 pm

Thanks again for all the great advice.

I'm in the third day of Gordon's recommended schedule (three coats, 1-2 hours apart, dry overnight, repeat), and I'll be heeding your advice re over-sanding, Barry. I'm also dry-sanding instead of wet-sanding per recommendations above. Will post back when I get it all re-done.
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Re: Sand-through with water borne lacquer

Postby Jason Rodgers » Mon Jan 29, 2018 1:17 am

Regarding dry sanding the General High Performance: I found it sanded easily up to 400, then loaded the paper (boogers, corns, whatever you call em) quickly at 600+. This led to backing up grits and oversanding, which caused sand-throughs. I took it all off and started over. The second time, I leveled at 400, let cure a week, plugged holes with paste wax, and wet sanded from 800-2000 (paper soaked overnight with a drop of soap), cure a bit longer, and buffed with medium and fine Menzerna. This worked well.
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Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Mon Jan 29, 2018 2:13 am

Jason Rodgers wrote:Regarding dry sanding the General High Performance: I found it sanded easily up to 400, then loaded the paper (boogers, corns, whatever you call em) quickly at 600+.

Interesting. I'll be alert to that when I get to the final sanding, Jason. Thanks!
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