Water-based lacquer - final coats? - created 09-07-2010

Baker, Daniel - 09/07/2010.23:04:48

I have never sprayed a finish before, and I am looking for some tips. I am using a Fuji HVLP sprayer and StewMac's water-based lacquer. I haven't played around too much with the sprayer, but it seems to be laying on a pretty smooth finish without any significant orange-peel or other common problems. Thus far, I have sealed the guitar with shellac and applied 8 coats of topcoat. I level-sanded with 320 grit dry paper, and have achieved a nice level surface. I am now looking for suggestions on how best to complete the job. The general drift of what I've read so far seems to be to apply a couple more topcoats, then wet-sand with 800 grit. Then wait a week and buff. Is that generally the accepted procedure? No thinning of the lacquer for these last coats? I read about doing a flow-coat, but that sounds a bit adventurous for my first time out.

Your general drift ought to work pretty well. I don't wet sand with the 800 grit. I clean the paper on a piece of carpet and wipe the dust off the finish surface every few strokes. That way, I can see what I'm doing. The water obscures the surface.

8 coats seems very thin to me. I would expect that your finish is somewhere in the area of .002 to .003" thick which to me, is a bit on the thin side. Waterborne lacquer sprays much much thinner than nitro.

If you can, peel off some finish off of a piece of masking tape or your soundhole cover or measure the masking tape+finish to get an idea of how thick your finish film is. I think that most are going for a finished thickness of about .004 to .006" with WBL which requires a rough thickness of .006 to .009".

If I were you, I'd spray at least another 8 coats (10 would be better) then wait at least 2 weeks (3 is better) and then start your sanding starting with 600g. Don't bother sanding before you let it cure for a week.

Ok, thanks for the suggestions.

Hi Daniel, I also use HVLP spray setup and have been using Stewmac Sealer and Topcoat for about 2 years. I don't know if you are using the sanding sealer first and then the Topcoat but this is what is recommended. I first spray about 12 coats of sealer and then between 9 and 12 coats of finish leave it in the Airing cupboard for a month to 6 weeks then wet sand to 1500 grit and then buff to a mirror finish.It works a dream every time.

John,

I used the sealer the first time I used this system but haven't bothered with it afterward, using 100% topcoat for the finish.

Do you have any idea what the point is of using half sealer/half topcoat? (real question, not trying to be sarcastic or anything).

Sealer has stearates added to make it easier to sand. This makes it easier to achieve a flat surface for the top coats. However it is also more opaque than un-adulterated top coat, so cuts down on the clarity of clear finishes.

Hi Andy, I guess Greg has given the answer in his first sentence. I have to say I have not noticed any lack of clarity in my finish. the use of the sealer is specified by the supplier to be about 75% of the finish and I'm sure they have a reason for this procedure.Finally from my own experience I have found that the longer the finish is left to cure the better the end result.

I used shellac instead of the water-based sealer. Everything I've read implies that shellac is suitable for a wide variety of topcoats, and imparts a nice look to the wood. My back/sides did not require any grain filler, so I didn't have to deal with that step in my process. So we'll see how it all works out. I wanted to have this ready in time for my wife's birthday, but all this talk of longer curing times has dimmed my hopes of making that deadline.

I've also used shellac as a base coat on all of my builds including the one where I used the sealer in conjunction with the top coat.

I'm planning on sticking with the 100% topcoat plan as it's one less thing to buy.

Hi Daniel even water will give a nice look to wood for a short time. One thing that you will learn in this game is patience defined in my Dictionary as "the capacity for calm self-possessed waiting" as different from Golf this is a game of perfect or as near as damn it is to swearing.

Andy, penny wise pound foolish !!

John, the topcoat can says it works fine on top of shellac. It didn't say anything about putting it on top of water though. So shellac is probably a little better, no?

Andy, penny wise pound foolish !!

Why?

Daniel how many coats of shellac are you putting on before the topcoat ? it's all about long term protection of the wood.

One less thing to buy Andy !

John,

With all due respect, on what are you basing your opinions?

Shellac is an outstanding sealant for wood and as Daniel stated, it makes the wood look nicer than straight water based sealer. In fact, Shellac slows the absorption of moisture from the air more than just about any modern coating, including acrylics. If you put down a coat or three of shellac, there's really no reason to use the sanding sealer. Shellac is one of natures wonders when it comes to it's universal sealing ability. It also has the advantage of being dissolved in alcohol so it hardly raises the grain when applied if at all (I seem to have seen it happen a little bit some times). Once applied, the shellac is an excellent barrier between the wood and the water in the finish as it's drying.

As to my 100% use of topcoat over shellac, I've heard no good reason not to. I like a hard finish as it's harder to sand through when leveling. This stuff cuts pretty fast as it is so in my opinion, there's really no reason to build the majority of coats with the sealer. I've done both and the results are the same or perhaps even a little better in terms of clarity with 100% finish.

Finally, although stew mac recommends building 75% of the finish with the sealer, the manufacturer of both the topcoat and sealer (Target Coatings) have no such recommendation.

I have a question about the waterborn lacquer. I have this touch-up gun that I want to use. If I'm spraying three to four coats a day, do I empty and clean the gun between each coat? Do I wait for the end of the day? Do I 'sand flat' with, say, 800 grit paper each day or between each coat?

I don't empty my gun while I'm waiting 2-3 hours between coats. I do scuff-sand with anything between 400-800grit, depending on drips, orange-peel, mistakes, but maybe not even sand at all or, even the next morning if all went well. If I stopped for the weekend, I'll scuff-sand, no matter how good it looks.

So then just empty and clean every night. Cool. Thanks!

For my last instrument I sprayed over 3 or 4 days with no sanding or leveling whatsoever (it was a burst so I was somewhat scared of sanding through) and it came out great - best finish so far.

Wait - I lied. I did a little sanding after some drop filling the rosette (a few missed pores). Only in that spot though, not the whole instrument.

One more thing - always, no matter what, your first spray should not be on the instrument. Touch the trigger for a second and look at the spray pattern. If it looks o.k., you should be good to spray. If it doesn't look like it did when it was freshly cleaned, you may need to re-clean. I wasn't emptying the gun after each coat (roughly two to three hours between coats) and a few times I noticed funny patterns that required cleaning to proceed.

I sometimes get a some build-up at the tip and have to wipe it off before shooting the next coat. And as Andy mentioned: Before each coat, I would verify my settings were still valid by spraying on a piece of carboard before putting a coat on the guitar.

Cool - good tips! I'm waiting for my pore filler to arrive, then I can try this. I have been trying furiously to get two guitars done before I move. We'll be living in an apartment for a while until we find a new house to buy, so I won't have a shop. Today I dismantled my CNC setup and packed away all my wood and guitar tools.

Good stuff, I probably have been doing a little (?) overkill on clean-up. After I spray a coat, I shoot very warm water through the gun for about 30 seconds. Then I take off the strainer and diaphragm and wipe them down, and take off the aircap and fluid nozzle and give them an extra rinse, check the little holes, and blow them out with compressed air. I don't take the needle out, but do blow the leftover water out of the gun by shooting some compressed air up through the feed tube. It only takes a few minutes, and my time isn't terribly precious at this point. I haven't had any variance in performance between coats, although I may be wearing out the parts faster with all that dorking around.

Do you guys do anything differently on the neck?

I've found when using KTM9 that warm water can actually cause it to set-up a bit. It gets most of the stuff out, but seems to encourage a slight film to build up inside the gun. Cold water works better, but slower. I switched to cleaning the gun with denatured alcohol, and that softened up the film, but wouldn't get rid of it without scrubbing, it left a gummy mess otherwise. When I finally started using acetone to spray out, all these problems went away.

This last build of mine, a classical, walnut and bearclaw sitka.

I had head shellac under epoxy often does not work well. I had experienced delamination of the finish when I used shellac under.

So this time, I used epoxy then the em1000 spray amber shellac from Oxford, the had some USL ( they don't make it anymore) and have put 9-12 coats on front then sides, back.

It looks great, hope the finish stay on.

I have never had any gun cleaning issues whatsoever with Oxford spray lacquer. I spray 3 coats per day and wait about an hour in between. It never gums up the gun.