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Lacquer Question - Pitting, Drop Fill
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Author:  klooker [ Tue Sep 27, 2011 8:33 pm ]
Post subject:  Lacquer Question - Pitting, Drop Fill
I'm working on my Padauk OM.

I filled it with Z-Poxy and sprayed about 6 coats of Behlen's/Mohawk Instrument Lacquer. My spray technique needs a lot of work. I put it on pretty heavy then sanded back to flat but I still have these tiny pits.

Do I need to drop fill, keep sanding back, spray it again?

Thanks,
Kevin Looker
Author:  Tony_in_NYC [ Tue Sep 27, 2011 8:46 pm ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
I would drop fill Kevin, but depending on how many of those you have, you might be spending a lot of time doing that so you might want to consider another coat. I brush lacquer so I would drop fill. Spraying a thin coat might do the job here as well, but I can't say since I dont spray.
Author:  Fleck [ Tue Sep 27, 2011 10:30 pm ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
That looks like "solvent pop". Spray lighter coats.
Author:  John Arnold [ Wed Sep 28, 2011 3:04 am ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
Yes, I see bubbles. Put more thinner in the lacquer, and spray lighter coats. There is no good reason to spray heavy coats of lacquer.
I would sand it a bit more, and lightly mist it with a mix of retarder and thinner before spraying a couple of additional light coats.
I generally end up spraying 8 or 9 coats on open-pored back and side woods like rosewood or mahogany. That is Mohawk with 25% to 30% thinner added.
I use water base pore filler after sealing the wood with thin lacquer.
Author:  klooker [ Wed Sep 28, 2011 9:01 am ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
Like most of my blunders, this was caused by rushing & not taking the time to pay close attention to what's going on.

There's never time to do it right the first time but always time to fix it later.

Thanks for the replies.

Kevin Looker
Author:  Stuart Gort [ Wed Sep 28, 2011 11:14 am ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
Granted that your problem may not be what I experienced...I just posted this to help inform others.

I can't tell from the pic whether there are tiny air bubbles trapped below the surface. A good look with a small magnifier would tell all. If there are a million tiny air bubbles trapped it is because the lacquer skinned over before the bubbles were released from the film. The volatiles, which cannot escape through the skin become bubbles. Intuition might tell you to add reducer and spray it thinner but adding reducer also promotes faster skinning. For this reason a small amount of retarder is needed. When you buy lacquer in a can, reducer and retarder ratios are worked out for you. When spraying with a gun, you have to figure it out for yourself....but you do need to use retarder if you want a wide latitude of processing performance with lacquer.

I was plagued with bubble entrapment and got a full dissertation on the subject by Philip at Mohawk Industries...one of the most helpful guys I've ever run across in over two decades of business experience. The COMPLETE solution for me was as follows:

1. Pre-mix a 10 parts/100 parts mix of retarder/reducer.
2. Mix 25 parts/100 parts of this retarder/reducer premix into your musical instrument lacquer.
3. Build 4 coats...wait a day...build 4 more (that's for electrics - acoustics go 3 and 3).

I use a pretty cheap HVLP gun for spraying. I don't know the orifice size but that will determine the reducer/lacquer ratio. If you need to go much more than 20% on the reducer/retarder mic, it might be better to cut the retarder/reducer pre-mix ratio to 5 parts/100 parts.

Spraying 4 coats and waiting a day solved a problem of slow drying as a result of using the retarder. As much as I'd like to pile on eight coats in one day, waiting this one day truly affected the cure time prior to leveling. The finishes I've sprayed since employing this technique are absolutely bubble free and can be leveled in two weeks...if not sooner. Prior to waiting that extra day I had to wait over a month to level.
Author:  klooker [ Thu Sep 29, 2011 10:05 am ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
Stuart,

Thanks for the detailed reply.

I don't think I have that many bubbles to deal with but what did you do to remedy the bubbles you had?

Kevin Looker
Author:  Stuart Gort [ Thu Sep 29, 2011 11:34 am ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
klooker wrote:
Stuart, Thanks for the detailed reply. I don't think I have that many bubbles to deal with but what did you do to remedy the bubbles you had?


Hehe...I'm a big fan of starting off on the right foot. I sanded it back down to the wood and started over...rigidly following the Mohawk plan. :)

1. Seal with vinyl sealer...reduced 50/50....vinyl/reducer (the ratio of 5/100 retarder/reducer as described earlier).

2. Fill pores with two fully sanded coats of sanding sealer...reduced 50/50 (same retarder/reducer ratio as step 1.) The vinyl clogs sandpaper easily but the sanding sealer does not. That's how you know you're down and through the sanding sealer....when the paper starts to clog. You really don't want to leave too much sanding sealer on the surface....a little is ok but clarity will suffer a little if you leave on too thick a layer.

3. Topcoat with lacquer...reduced 25/100 with 10/100 retarder/reducer.

I pretty much HATE sanding cured vinyl sealer so I've used shellac as a sealer too. The thing nagging me is Mohawk's suggestion that the vinyl, sanding sealer, and topcoat are all nitro based and they burn into each other forming a molecular bond from start to finish. This means optimal adhesion to the wood...which is a big priority for me. I like shellac a LOT better as a sealer...the smell, the sandability, and the application with a cloth wrapped cotton ball. But the adhesion could be compromised since the bond between the shellac and the sanding sealer is mechanical...not molecular. I could be wrong about that but on this site and others people seem to thoroughly embrace the idea of shellac as a sealer and vouch for the bond between shellac and lacquer. I asked Philip at Mohawk specifically about this and rather than suggest to use their shellac as a sealer...he was pretty adamant about using the vinyl sealer...emphasizing the molecular bond to the rest of the system.

Here's what I'm thinking. The sanding sealer burns into the vinyl for a chemical bond. But if shellac is used as a sealer instead, the stearates the make the sanding sealer highly sandable will further compromise the mechanical bond that occurs between them. In our conversations we never specifically addressed this combination but I was left with the impression that there would be no comparing the two combinations of shellac/sanding sealer and vinyl/sanding sealer....The latter was clearly superior according to Philip.
Author:  John Arnold [ Sat Oct 01, 2011 5:51 pm ]
Post subject:  Re: Lacquer Question - Pitting, Drop Fill
I have never liked sealers under lacquer, either due to workability, color, or clarity problems.
For over 30 years, I have sealed with the same lacquer I use for a topcoat....with zero adhesion problems. Before I used nitro regularly, I followed the same routine with automotive acrylic lacquer.
The only problem I have encountered is occasional fisheye with oily woods. But it normally can be handled by drop filling.
After sealing with a couple of thinned coats of lacquer, I use water base pore filler on the porous woods. Early on, I discovered that the acrylic lacquer would not adhere to oil base filler, so I started mixing my own water base filler in 1979. It is nothing more than Elmer's Carpenter's Wood Filler mixed with dark brown latex paint and a bit of water.
The rest of the 'program' is straight from Mohawk's data sheets.
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