Primer/sealer bubbled (in sun) - Part 2

[ezas]

I'm doing an Alder body and decided on wanted to seal it to help me decided if I wanted to clear finish it and I liked the idea of a sealed body for even absorption of what ever went over it.

I used Bullseye 100% dewaxed SealCoat (Shellac) and thinned it about another 1/3rd with denatured alcohol. I built up a few layers and sanded it back. So far so good.

After seeing it sealed I decided to paint it instead of a clear finish. I got some 1 part polyurethane loaded into a bomb at an automotive paint store. I asked about Primer because I wanted to use it to see how my surface was before painting. The guy at the store said be sure to use Lacquer based primer. So I got a bomb of a lacquer based primer. So far so good.

Now things take a turn. I kind of fudged it up by spraying it too dry (too far away) but with enough spraying I had complete coverage (but ended up with a thick coat). Once dry, i knock the surface back with sandpaper. And hung the guitar to completely out-gas before moving forward. On the 2nd day I hung it up outside and forgot about it and in the afternoon the sun was hitting the black primer and my brother noticed it was bubbling. But only in a few places. So I sanded it back and what I noticed was that where it had bubbled was where it seemed like there was a bit more sealer built  up. After removing the primer the sealer was so hard that I couldn't sand it back and had to use a scraper (which worked fine).

So what happened? Is there a problem using Lacquer primer over Shellac Sealer? Was my sealer not 100% dry? Remnants of mineral spirits/naptha under the primer?

My guess is that the sanding sealer was not full outgassed and the heat of the sun on the black primer 'baked' it too fast.

The guitar is sealed and sanded again and I'm giving it a few days to fully/fully dry. I'd still like to do a primer coat but want to skip the whole bubbling/sand back exercise. If I let the sealer really dry and keep black primer out of the sun should I be okay with this schedule:

Shellac based sanding sealer - sanded back close to bare wood
Lacquer based auto primer (as double check for smoothness before color)
Single part Polyurethane paint
Clear Coat (having sprayed at automotive body shop)

I realize that the sealer/primer coats are probably not needed but it's a schedule I'm comfortable with to get a good result.
==========================

Well I shouldn't have been so comfortable with my schedule. In spite of letting the sealer coat sit for two days in warm temperatures, and the primer sit for over 24 hours, it bubbled under the paint/clear coat. Anywhere it wasn't sanded back to close to bare wood bubbled. Apparently the primer was letting it gas but as soon as it was painted and cleared, which happened within a few hours, it bubbled in places.

Oh well live and learn. This will only be the third time back to bare wood. But good news is I have a good idea on how to work with the Poly paint I'm using and get good results. Except for the bubbling in a few places the finish came out good. I'm also not crazy about the color, so this will be chance to change it.

I'll be skipping the sealer this time. I only used the sealer originally cuz I was mixed on natural vs a painted finish and I just stayed with it since I started with it.

I prolly should have done a test stick but this is my learning guitar so no harm no foul.

 

[stubhead]

There's one sealer on there when you get it, just a dip in something. The Bullseye is good stuff, but I've only used it to lock a dye into the body so it didn't run into the finish. And like you, really thinned it. It needs, like nothing - just to get it wet with the stuff, and it'll dry in a day. I do try to use water to raise the grain and sand it back before anything else, even up to 3 or 4 times. Then the Sealcoat doesn't seem to raise much of anything.

 

[ezas]

Yeah i just thinned it until I liked the way it wiped on. Part of my reason for using sealer  was because I sanded thought through the sealer that comes on the body.

 

[Patrick from Davis]

The Zinsser stuff is probably not the probably not the problem.  I have never thinned it, just slapped it on.  It is dissolved in alcohol, and that gasses off very fast.  So it was probably fine by the time you put the primer on.

However, Urethane top with lacquer primer sounds fishy.  Lacquer is nice stuff, but you generally want to stay with one type of finish at a time.  A urethane primer would be what I would use.  Also lacquer takes quite some time to gas off and harden up.  The finish coats you wait for three weeks before leveling and polishing.  They still seem a bit soft after that amount of time.  But, the thick coat would be a problem for the solvent to migrate out because you are putting a candy shell on the exterior of it.  But it still has to go somewhere.  I would sand off the stuff, and get a urethane primer and go from there.  In general it is a no no to mix things up finish wise.
Patrick

 

[Patrick from Davis]

One other thing, those times are for rattle can applications. From a gun the amount of solvent is much less and so the process is faster.  But out of a rattle can, it takes quite a while to get rid of all of the stuff that is there so it goes on properly.
Patrick

 

[Tonar8352]

I've been on job complaints where the painter complained that black paint bubbled and when we asked them how hot was it when the product was applied they said only 95 degrees.  I met them on the job with a surface temperature gauge and the surface read 185 degrees. Your finished got cooked.

 

[ezas]

Yeah black primer in the sun was not my finest moment.

The lacquer based primer was what the guy who sold me the paint told me to use under the paint and that is at a store that sells nothing but automotive paint. PPG, Dupont, etc. The primer was bought at an auto parts store that has a separate wing and dedicated staff to paint and paint supplies.

I think the lacquer and primer are fine since it only bubbled in places and only on the side in the sun. But still wanted to get some opinions. Im really letting each layer dry this time. I have the sealer sanded back to almost bare wood but stopping before sand through and I'm still letting that thin layer take a couple of days to gas off. It's hanging outside in 90 days but this time only in the shade!!!

I didn't mention it but I also got to learn about print through of fabric texture 24 hours after applying the sealer. I thought being pretty thin it would dry pretty fast. Guess not.

It's my first guitar and meant to be a practice/learn guitar before doing a nicer guitar for a friend.

Edited to add: I'll ask about urethane primer at the auto paint store. They are super helpful and nice.

 

[stubhead]

Auto paint is for painting autos that are expected to survive some pretty extreme conditions, though - unless you're planning on driving your guitar through the Kalahari Desert (on the way to your snowstorm gig) you might be able to get by with something just a teensy bit easier to do. I guess it would be handy to have a guitar that could paddle your boat or decapitate an alien robot. YOU JUST NEVER KNOW....

 

[Patrick from Davis]

It is not that the lacquer primer and the urethane top coat won't work, there are plenty of examples of mixing products around here.  It is just one of those things where you are hoping the chemistry will work out.  With like brands of the same chemistry products, you don't have as much of a chance with having them not be compatible.  If I am using Deft nitro, I'll use Deft nitro primer.  There are several examples around here where bad things have happened when mixing products, and it is not much work to get the primer that goes with the top coat.  You were given the advice from someone at the store who presumably has much more experience with this than I do, which means that it should work.  But it is one of those things that makes the alarm bells in the back of the head go off for me.
Patrick

 

[ezas]

I've definitely considered the Auto body paint is for very harsh condition angle. And I have browsed the DIY Finish thread like 20 or 30 pages deep. But I like the depth of the color and I was going to ask them not to build up too much clear coat. Also I need this 'practice' guitar to move along so as not to hold up the nicer guitar (that one is pre finished body) that I'm also doing. So the quick cure times is a plus for me.

Krylon has a color I like but the 3 week dry time holds up my buddies guitar. I could skip the primer since it's not really needed. I was using it more as a coat to find finish flaws since this is my first body and to get some practice spraying with a bomb. I'm not new to rattle cans I did a lot of work on my motorcycle with rattle can, but none of those parts had the odd shape of a guitar.

Anyway that's my thinking on some of these things. I don't mind fudging a few things up along the way.

But all the input is good, thanks

 

[ezas]

The lacquer based primer and the single part Poly were fine together. It was the shellac sealer which was the problem. See the update to my first post.

 

[Cagey]

I doubt that it was the shellac. That's the "go to" film used to create barriers between incompatible finishes. It's more likely you didn't wait long enough or treated the finish badly during the interim period between coats, which you've admitted to.

Good finishes take patience, no matter what you use. You'll notice that Warmoth's delivery times increase dramatically if you want something finished. Finished or unfinished "Showcase" part? A week or two, tops, and it's ready to wreck. Clock's already run out on those parts. Custom or made-to-order finished part? 8 to 12 weeks. It's not because they don't like to do custom work, it's just that it takes that long if you want good results. You rush it, and you end up with problems.

 

[stubhead]

Ye Olde Sniff Test is pretty reliable. If you can still smell something - IT'S STILL GASSING, DUDE. I mean, what is it you think you smell. And yes, this means Tru-Oil has to sit a month, and nitro has to sit a month, and... and... the big pro guys do have some ways of accelerating it, heat and ultraviolet(?) I think, but don't just throw it in the oven or the tanning bed.