Stupid bubbles in the finish coat!!

[kirshman]

Why does this happen sometimes?!  I have my enclosure perfect, then when spraying on the high gloss laquer, or any other finish coat, i'll spray 5 pedals at once, in the same way, and 1 will have all these little bubbles in the clear coat and the rest won't.  Is it my technique; is there something else I could be doing to avoid this?  I usually spray on the topcoat in 4 layers all spaced 2 to 5 min apart then throw it in my toaster oven.

[AC_FX]

I'll try to help, but I'll qualify it all by saying this first:   finishing  with pro results is hard.  Sometimes you'll never have any damned idea why things went south, you just have to start over from wherever it's necessary to get the right results.  Take it from a pro who knows.

Having said that -

Are the bubbles there before you bake the enclosures?  If not, quit baking them and/or let them cure overnight before baking, and see what happens.  Also - why are you baking them and is the finish designed to be baked?  It may well be, but I ask because there's a common misconception that baking any finish will make it more durable or safely speed things along.

Are you getting down to the last of the finish in the cup by the time you spray the last enclosure?  Maybe the finish is slopping around in the cup and letting the gun/can get some air in the finish?


Are the bubbles milky, or clear?  If they're milky spots, it's moisture trapped in the lacquer, you're piling on too much too fast, and the humidity in the air is just getting trapped in the finish as it cures, instead of evaporating with the solvent.  Use thinner coats, more time in between, and maybe some retarder.

[eldredracing]

It may help to bake the parts after cleaning, but before spraying.  This will help outgas the metal which is especially a problem in cast parts.  I'm not sure what you are baking the parts out, but you could try and see if it helps.  See link below:

http://www.powdercoatguide.com/2013/08/cleaning-and-degreasing-is-step-1.html#.Vbe4K_lVjYY

[Beaker]

Paint spraying is all about the preparation - jusk ask any vehicle refinishing technician.

What products are you using - it can make a huge difference?

It's hard to say exactly what the cause of your problem, but it sounds like moisture blisters, or what's known in the trade as solvent pop.

Moisture blisters will form if you try spraying on a humid day. It tends to produce blisters of varying size and shape.

Solvent pop results from not allowing enough time between coats, drying too fast or when spraying too thick - the carrier solvent is still trying to escape from the previous coat. 2-5 minutes between coats sounds a little too quick to me. Solvent pop tends to form a rash of tiny regular pinhead blisters, often confined to one area,

The toaster oven may be the culprit too, if it is too hot, as the top coat hardens before the solvent from the previous coats has not had time to escape.
As AC says, why are you baking them? His advice there is spot on.

I know this is aimed at vehicle techs, but it may help:

http://www.standox.com/content/dam/EMEA/Standox/HQ/Public/Documents/English/Standotheks/THK_Paint_Defects_GB.pdf

[rocket88]

speaking from experience of painting and baking my all my enclosures i sell. if it's just tiny bubbles it just happens. sometimes it's actually little flakes of dust that got stuck in the clear but you didn't notice, other times its in the prepwork.

here's my steps:

1: sand the enclosure to make it as flat as possible. this goes for whether or not i'm etching the enclosure. i wet sand up to 800 grit, starting at 320 grit, but in all honesty you can really stop at 400 grit, just force of habit to go to 800 for my brushed enclosures.

2: wipe the entire enclosure down with acetone. i do this until i don't see any residue or discoloration. then i do it one more time just to be safe.

3: i move the enclosure to my painting area holding it with the acetone towel so that i don't get any fingerprints on it. once i set it down i leave it for 2-3min just to make sure the acetone evaporates.

4: i lay down my base coat thin, but so that the entire enclosure is a single uniform color. i move it to my baking pan, and place it in my special toaster oven for enclosures at roughly 150F for 30min.

5: let it cool for 10min, then move it back to the paint area and do the same thing for 1-2 more coats, with each coat being baked and cooled.

6: i lay down the clear in a medium thickness coat and bake it. same process 150 for 30min, cool for 10min, and lay down a second coat.

now if i see that there's something in the clear or looks like a little dust, i just lightly wet sand it with a high grit sandpaper, 600-1000 grit, just enough to level everything and spray one more clear.

for me, i've found that sometimes too much clear is bad and causes fuck ups in the clear, so i try to limit my clears to 2 layers, 3 max. btw,  i use duplicolor automotive paint, which is super durable and comes in a wide range of colors.

also, ac, baking the paint helps speed up drying/curing time, gets the gases from the propellents to evaporate quickly and more completely, and actually makes it harder and more durable. think about how paint is applied to cars at the factory or when it's repaired. they bake the paint after it's applied.

[Beaker]

Zach you are spot on with your prep, but I agree with AC - both solvent and water based auto paints are designed to be baked - usually between 35 - 50 degrees Celsius.

However many spray can products - even some aimed at the auto market, are not.

[rocket88]

beaker, i just checked the paint can, and no mention of baking temp or time, and i also checked the setting on my little toaster oven, which is at 150 F. the range you gave is roughly 95 F - 122 F. that means i do it a little hotter, but since it's the first temperature with a numerical setting that's where i set it. so far no issues with 150 F, which is roughly 66 C so close enough for government work.

i did do some research and of all places i found a lot of guys that do gun rebuilds, and pinewood derby cars, amongst a few other random places, for duplicolor it's suggested between 150-200 F, but never over 200.

[Beaker]

Zach, I know you well enough to know that you will have done your homework, read the data sheets for the products you use, and are following the manufacturers reccomendations - so absolutely no criticism of your method was intended.

BTW I said 35-50 degrees, I should have said spray at 25 - 35 degrees, and bake at 50 - 70 degrees Celsius typically. New cars rolling off production lines get baked at up to 180 degrees - that's 350 degrees Farenheit.  However the paints used are designed to be baked at this temperature, typical motor store acrylic paint would catch fire at this temperature!

Referring to the OP, I suggest that the problem is solvent pop, caused by either too thick a coat of paint, insufficient flash off time between coats, or drying too fast due to too high a temperature (or possibly a combination of these). Many of the toaster ovens I have looked at seem to have a minimum temperature setting, that is possibly too high for some paints. This is where I agree with AC FX, as many acrylic spray can paints especially the cheap ones, are not designed to be "baked" (gently warmed maybe a better option), and may not benefit from it. It may not make some paints tougher.

What we don't know, is what particular brand of product Kirshman is using, whether it is acrylic or water based, and what the manufacturer reccomends for best results.

[rocket88]

Very true buddy. I didn't think you were giving any critism or anything, just adding to the convo after doing some research. Figured if anyone wants to follow what I do since I've got some good results, I would give as much info I could. It's all good man, trust me, I think we know each other well enough by now to know when there's criticism and when to take offense. I don't think you and I ever have to feel like we need to walk on eggshells when talking.

Also, it's really interesting how some car companies bake there paint. Many companies have different temperatures depending on the material too, since some parts need to flex, and others don't. That means that some cars get painted before assembly, which does take longer then being able to paint the whole car at once. Really neat stuff.

You're totally spot on about some paint igniting at to high of a baking temp, I've seen it happen. When I saw it, it happened because the gasses escaped at such a rapid rate, that it built up in the oven, and the heat made it go boom. Not to mention using it as a propellant in a potato cannon back in high school when we ran out of our "normal" propellant. It's amazing myself and friends are all alive and in one piece.

Anyway, back on topic, we need to know brand and type. It can make a huge difference. Even I just normal drying times without backing.

[kirshman]

Hey guys, thanks for all the great tips!  They're uniform sized bubbles that are clear.  I'll try and spread my times out and maybe a few less coats.  The stuff I'm using is also duplicolor, the automotive rattle can, so I wouldn't think it's the low heat, but if the other things don't work I'll try that.  I just wish it was consistent so it'd be easier to figure out.  Thanks for all the help though guys, I appreciate it!

[rocket88]

that what i use kirshman, so no more then 200 F cooking temp, and like i said i stick at 150 F for 30min. also, try doing only one or two at a time. i've found that when i've done a bunch at the same time by the time i get to the last one all the dust and shit in the air ends up on that one. doing one at a time seems to lower the instance of it happening too.

[Beaker]

Spray painting is a black art, practised by true Zen masters.

It takes many years for pro auto shop guys to learn to compensate for the almost infinite combination of factors that can affect your finish - anything from the weather outside, to what kind of mood you are in, can, and will affect the finished product.

What can give totally consistent results for three days straight, might produce a right old mess on day four.

So don't beat yourself up Kirshman, just try to get your prep right, slow down and take it easy, and try to follow the instructions as closely as you can.

If you still have problems, emailing Dupicolor for advice will almost certainly get you expert help - direct from the horses mouth.

[kirshman]

You guys are awesome thanks!  By the way Zach, I'm still anxiously awaiting your etching process, especially your dual color etches.