StewMac Spray Lacquer over Rustoleum Spray Lacquer Problems

[Inklings]

Hi Folks,

I'm refinishing a banjo peghead. Some of you recommended using this Rustoleum Spray Lacquer for the black surface.

I used it - it went on like a dream, wet sands really well. However, I needed to apply a decal to it, and then finish over top with a final semi-gloss/satin coat. The rest of the neck is finished with StewMac Spray Lacquer, so I thought I'd use that.

Unfortunately, the StewMac spray caused deep cracks in the finish of the Rustoleum stuff. Has anyone sucessfully applied a finish over the Rustoleum, and if so, what did you use?

[Br1ck]

I use gloss white Rustolium as a primer for strat and Tele bodies, then paint the color and clear coats with ReRanch nitro laquer. Never had a problem.

I like the gloss for primer because when you sand it,many low spots stick out like a sore thumb.

And don't dare spray nitro without a respirator.

[Greg Mirken]

Mixing brands is always risky, and it's prudent to test on scrap first. The Rustoleum product may not have actually been lacquer-based. It would be safe to use Stew-Mac black lacquer under their own clear. Sounds like at this point you have to remove all the finish from the headstock and start over. If you have to, try Zinsser Seal-Coat between the Rustoleum and the Stew Mac clear. Test on scrap!

Greg

[rcc56]

I just looked up the Rustoleum in the link the OP gave. It is an acrylic based lacquer. The Stew-mac lacquer has a nitrocellulose base. Apparently, these two products do not mix.

Your best bet is to strip it and respray it with products that both have the same base. If you try to fix it, it might take you twice as long as starting over from scratch. Or problems might turn up later as the finish cures. Spraying Stew-mac clear over Stew-mac black is the best solution if you're going to be using spray cans.

If you continue to mix products with different bases, you're likely to spend 100 dollars trying to save a dime. Or spend 20 hours trying to save an hour's worth of sanding.

[HoGo]

After reading OP I would say the first coats were not cured enough for the top coat or you applied too heavy topcoat at once. If you are using the same lacquer you risk less as it willl be shrinking/curing at similar rate but mixing two products with different rates can lead to cracking especially if the upper layer is harder than lower, the lower will absorb some thinner but the outer layer will soon dry to hard crust over slightly softened layers that will slowly cure and cause cracking
Quite a few times I finished over various (sometimes unknown) finishes but they were always well cured. The only problems I had was with adhesion when old finish was contaminated. I even French polished over catalyzed polyurethane while some folks told me it cannot be done.

[Inklings]

I just looked up the Rustoleum in the link the OP gave. It is an acrylic based lacquer. The Stew-mac lacquer has a nitrocellulose base. Apparently, these two products do not mix.

Thank you - I had not realized that there were so many types of Lacquer! I think this is probably where my error lies - the two products have different bases.

After reading OP I would say the first coats were not cured enough for the top coat or you applied too heavy topcoat at once. If you are using the same lacquer you risk less as it willl be shrinking/curing at similar rate but mixing two products with different rates can lead to cracking especially if the upper layer is harder than lower, the lower will absorb some thinner but the outer layer will soon dry to hard crust over slightly softened layers that will slowly cure and cause cracking

This is a great explanation - thank you! It makes sense to me, and I appreciate you walking me through what most likely happened.

Br1ck - did you use the acrylic based rustoleum as the base coat?

I am in no way married to using the StewMac Nitro as the top coat over the peghead. I do really like how the Rustoleum product builds - as others have noted, it is a great solution for this application. If someone has a top coat they've used successfully over it, I'd love to know, as I'd like to use it again in the future. Otherwise, it sounds like the advice to let it sit a while before attempting anything over it is probably wisest.

Thanks also for the suggestion to try on a bit of scrap. I didn't make the neck, so I don't have an identical piece of wood, but it's a point well taken for the future. I have a suspicion that this reaction could be duplicated, even on a scrap piece of pine. If I get some time, I'll test that out and report back. A test piece is also in order to figure out what will work as a top coat.

[Paul Busman]

Leave those cracks and call it "distressed". People go to great lengths and expense to make it look like someone has actually played the instrument.

[multidon]

It used to be that when the word “lacquer” was mentioned, you could assume it was nitrocellulose we were all discussing. Not anymore. The term “lacquer” is almost as meaningless these days as the term “varnish”. You almost have to be a chemist to figure it out.

There are even variations within nitro lacquers. All formulae are not equalivalent. Some cure softer, some harder. Some cure faster, some slower. Some catalyze, some do not. They are all a witches’ brew of solvents, plastisizers, retarders, catalyzers, and so forth. The Gold Standard for instrument finishers used to be McFadden, I believe Seagrave might use the same formula now. But all of the nitro based lacquers have one thing in common besides having nitrocellulose as their solid base. They are mostly manufactured for the furniture and cabinet industries, not primarily for musical instruments. Characteristics important to instrument makers and users may be different from those of the furniture makers.

I don’t know what each manufacturer uses, but I do know Weber uses a non catalyzing lacquer, because they say so. My glossy Bitterroot gathers micro scratches if you just look at it. It seems soft. My Gibson guitar seems to have a much harder nitro on it.

It’s best to use the same brands and even the same lines within brands. Use Stew Mac black if you’re going to use Stew Mac clear. Or, does Rustoleum make a clear version of their acrylic lacquer? Acrylic on a peg head doesn’t strike me as a particularly bad idea. It might resist scratching from string changes.

[Inklings]

It’s best to use the same brands and even the same lines within brands. Use Stew Mac black if you’re going to use Stew Mac clear. Or, does Rustoleum make a clear version of their acrylic lacquer? Acrylic on a peg head doesn’t strike me as a particularly bad idea. It might resist scratching from string changes.

Thanks, Don. I think I see what you mean. Looking for a clear version like this makes a lot of sense! I may pick up some of that, and give it a try over the black, on a test board.

Nothing against StewMac black, it's just a few people here on the board talked about how fast this Rustoleum product was able to build, and I was anxious to give it a try. I'm seeing how keeping within the same brand family makes a lot of sense. As you note, it seems the words on the can aren't universal in their definition.

[thistle3585]

I had that issue once and put a coat of shellac on it to seal it before going with lacquer. I ended up stripping it, as I didn't like how the color came out, and ended up using reranch product as the base coat.

[Inklings]

I started the test coats last night on a scrap of pine in the shop. Will build those for another day, or until I think there's a similar depth to the finish on the headstock that cracked.

I picked up the Rustoleum Clear product as well, so once the black has set up, I'll spray over it, and see how it turns out.

[Br1ck]

I really don't know, but it was at a big box store with all the Rustolium products.White or black. I remember I was in a bind for time and didn't want to wait for what I'd been using. I have not had a problem with shooting nitro over it in four or five uses. I'm in 80 degree and 30 to 40% humidity conditions. I do tend to wait two or three days to sand it flat before the color coats go on.

I also shoot multiple light coats.

[Inklings]

Just to further the scientifical investigation side of this here thread, I will post this photo:



Note: Lines in the surface are the floor joists above - that is one shiny surface!

This is 5-6 coats of the Rust-O black, top coated with the same brand in Clear. The bottom coat of black was allowed to cure for over the manufacturer recommended 24 hours. It was then level sanded with wet 220 paper. I have sprayed 2 coats of clear over it at the moment.

No cracking, or other issues. I think this is going to be the way forward for the peghead, and thank you to everyone for the advice.

Finishing is a whole world of its own. Thanks for the navigation guidance, folks!