Sealing colours under lacquer

[Tavy]

Here's my conundrum, I have some colours which I know leach/spread really badly with alcohol (so shellac sealer is out), and with lacquer thinners - and ultimately I want a lacquer finish. They're perfectly fast under water based finishes (EnduroVar for example), and under oil based ones (TruOil etc).

So my question is what sealer to use in this case?

And yes, I should have thought about this before agreeing to do lacquer

Only thing I can think of at the moment is to spray a really thin spit coat of lacquer outside on a hot sunny day.

[poul hansen]

I haven't tried but there is a waterbased porefiller, that will seal the surface.

[Jim Hilburn]

Don't try spraying lacquer in the hot sun. It doesn't work well in my experience. I think a thin coat of shellac lightly airbrushed is the best way.

[sunburst]

I seal alcohol soluble dyes with a couple of sprayed coats of shellac. The spray is barely more than, and perhaps could be considered, a mist coat.

[Jim Hilburn]

It will probably go on with a little texture but as long as it doesn't go on very liquid it shouldn't lift the color.

[Tavy]

Thanks folks, I was hoping to avoid spraying as other than "emergency" rattle can lacquer I don't have spray gear here. But yes, I agree that the thinnest least wet possible coat is the way to go whatever it is.

[Tom Haywood]

I've had good luck with Pre-Val sprayers to get thin even coats of shellac. Five bucks or so, plus a nice reusuable glass bottle.

[Chris Pile]

TruOil applied with your finger in thin layers.

[Tavy]

I've had good luck with Pre-Val sprayers to get thin even coats of shellac. Five bucks or so, plus a nice reusuable glass bottle.

I clearly live on the wrong side of the pond: more like 20 bucks over here, but I wasn't aware of those, good tip - thanks!

[Dale Ludewig]

FWIW, you can't spray lacquer over TruOil successfully.

[HoGo]

FWIW, you can't spray lacquer over TruOil successfully.

I wonder why?
You can certinly apply shellac over Tru-oil. And shellac will accept Nitro...

[sunburst]

Shellac used to be considered the universal undercoat/overcoat, being compatible with nearly any other finish. It still is... sort of... but I, as well as others, have been bitten by the assumption that shellac is still universal.
It might be that lacquer over shellac over Truoil would work, but I for one don't intend to try it and see.

BTW I am currently stripping finish from a project. I applied it following standard procedures backed by 35 years of experience only to find that the finish failed before I could get it buffed out. Sometimes building and finishing instruments can be completely demoralizing.

[rcc56]

I figure all bets are off with the abundance of modern finishes that have come into use over the last 20 years.

And yes, lutherie can be utterly demoralizing when things go wrong, no matter how much experience you have and how much care you use.
I'll cross my fingers for you, John. Maybe a couple days away from that project would help you to get back to a good state of mind.

[sunburst]

...Maybe a couple days away from that project would help you to get back to a good state of mind.

I've been venturing back in some, but I stayed away from the place for a couple of days. I've learned when it's best to walk away.

[Chris Pile]

FWIW, you can't spray lacquer over TruOil successfully.

Untrue. I've done it, and so have others.

[HoGo]

Untrue. I've done it, and so have others.

That's why I wondered why he asked.... Perhaps the formulation of T-O changed or his surface was contaminated? One never knows these days as John noted.
I wouldn't apply nitro over thicker layer of T-O as that would likely cause cracking (hard finish over soft) but if the T-O is used just as a selaer/filler with minimal to no coat above wood it should work OK under shellac or nitro.

[Tavy]

BTW I am currently stripping finish from a project. I applied it following standard procedures backed by 35 years of experience only to find that the finish failed before I could get it buffed out. Sometimes building and finishing instruments can be completely demoralizing.

I feel your pain John, we've all been there, but sometimes the only way is to back up and go over

[sliebers]

Not all nitro is compatible with a shellac sealer. Seagrave and Behlen worked well. I switched to Cardinal a few years back and had adhesion problems after it cured.

[Jim Hilburn]

Bullseye makes rattle cans of shellac but I'm not sure if it would be like their Seal Coat or like the old waxy stuff everyone warned not to use.

[amowry]

Not all nitro is compatible with a shellac sealer. Seagrave and Behlen worked well. I switched to Cardinal a few years back and had adhesion problems after it cured.

Yes, if you're using Cardinal lacquer, definitely do not use shellac as the sealer. It might work, until it doesn't . I use a thin coat of Seagrave vinyl sealer, which works great under Seagrave or Cardinal nitro (probably others too). As long as it's not sprayed too heavily it won't cause dyes to bleed (but it still "wets" the dye well). There are those who say shellac looks better than vinyl as a sealer, but I did multiple test panels and couldn't tell a difference in appearance. Vinyl also adheres to celluloid like crazy. The caveat with vinyl sealer is that it has to be "fresh" for lacquer to stick to it, so I always spray another thin coat 1/2 hour before the first coat of lacquer.

[Chris Pile]

I wouldn't apply nitro over thicker layer of T-O as that would likely cause cracking (hard finish over soft) but if the T-O is used just as a selaer/filler with minimal to no coat above wood it should work OK under shellac or nitro.

Are you thinking of Watco oil finishes, which remain soft?
TruOil does get hard, provided it's applied properly in very thin coats.

[HoGo]

Are you thinking of Watco oil finishes, which remain soft?
TruOil does get hard, provided it's applied properly in very thin coats.

In my experience Tru-Oil (the real one) doesn't get far past "hard rubber" stage. Is quite flexible and will often not crack even at deep ding in spruce. Typical nitro is harder and more brittle, though there are exceptions and diffrent formulations. I've used shellac french polish over Tru-oil, sometimes it can craze finely over time (year or two), but that's often seen in vintage instruments so it's OK with me.

[rcc56]

Tavy, I don't have spray equipment either. The only suggestions I can give you if you're not using a compressor and spray gun are:

1] Get out the test boards and use some different colors [water based or oil based] instead of whatever you usually use.

-or-

2] Farm out the sealing coats to a cabinet maker with spray equipment.

The last rattle can lacquer I used, which was Mohawk, had so much thinner in it that I had multiple problems; and it took forever to get the job done.

I don't trust pre-mixed canned shellac for much of anything. I've always used dewaxed shellac flakes dissolved in pure grain alcohol.

[Tavy]

I don't trust pre-mixed canned shellac for much of anything. I've always used dewaxed shellac flakes dissolved in pure grain alcohol.

+1 on that, I've always used my own blonde shellac / gum sandarac mix.

[Richard500]

For spraying thin materials on small areas, an airbrush setup is sufficient. A full-size compressor and gun isn’t needed. Often, decent airbrush equipment turns up at garage (tag, yard) sales for very little money. There is, as in all spray applications, a learning curve, but its probably related frustration that makes these things surplus.
Mostly a matter of trying different thinning and spray distances. The small units, I think, have no pressure regulators.

I’m guilty of seldom shooting enough test boards/coupons before doing the actual work, and this is, indeed, not good practice, especially if there’s an issue with poor drying, etc. Experimenting with different or new materials, as sealers, fillers, stains and topcoats really demands lots of tests and time.

Worse, my reliable paints here in the US seem to have changed formulations, probably because of VOC restrictions; what used to be V&M Naptha is illegal in my state, and I’ve been surprised with new and ugly problems. Meanwhile, the decade-old can of pre-mixed shellac still works fine (for French polishing), so it doesn’t get replaced. For my purposes, if there is a slight color issue, I can’t see it. What’s on the store shelf now is probably different.