Bumps

I am no painter, but am pretending to be one.
Yesterday, after days of filling pin holes, careful prepping and priming, I shot an Acry-Glo Silver Gray color coat onto the wheel pants of my RV. After mixing, I filtered the paint through a paper filter en route to the gravity feed bowl fitted to the paint gun. I applied a tack coat, waited about 1/2 hour..... applied another coat....waited another half hour...with NO bumps to be seen....then applied the final wet coat. From a few feet away, they look great with a nice "wet" finish look. Unfortunately, upon close up inspection, the surface is flecked with many "bumps". It feels rough when you run your fingers across the surface. Several days ago, I shot the empennage tips using the same product and they turned out perfectly. My questions are these. What might have caused this? After a few days of curing, is it possible to wet sand the bumps out, yet still retain the paint finish's brilliant "distinction of image"...or luster? If so...what grade of sandpaper should I use? Or should I rescuff the surface and try again? I am willing to do that if necessary, however, would be nice if I could trace down the cause of this problem so it does not happen again. After all, that paint ain't cheap, even if I am applying it myself.
Rick Galati RV-6A "Darla" 122 hours

Wet sand them off as soon as you can, it will be harder after the paint hardens. Buff them out when you feel the paint is hard enough to handle your pad. Not sure what caused this but it looks like foreign debris either from dried paint in the guns tip or just small airborne trash.

-Jeff

Perhaps it's "blistering" - some solvent effect on your pin hole filling.

http://www.sherwin-automotive.com/reference/troubleshooting_guide/blistering/index.cfm

Could the pin hole fillers not have been completely cured??

gil in Tucson

It really looks like solvent popping or blistering to me. What was the temp like in the booth? If they are blisters, sanding will just chop the tops off them leaving a hole. I wouldn't do anything until I figured out what caused the problem.

Yes, I've seen that and experienced those blobs from water condensing out with the paint spray. Check to make sure your dryer is operational and the dessicant is OK. Make sure you have a good water trap in your line where it comes out of the tank. The dryer unit should be right at the "End of the Line" just before the short airline to your gun.

Cheers, Pete

Prof.Plum+Candlestick+Library

az_gila said:

.....http://www.sherwin-automotive.com/reference/troubleshooting_guide/blistering/index.cfm
............gil in Tucson

Click to expand...

Gil,

Thanks for the informative link. After some amateur deduction attempted by this determined dilettante, I now strongly suspect the cause was high ambient humidity and a relatively low temperature of 70 degrees. In fact, anxious to get the job done, I shot the paint in my open garage while outside it was raining on and off again. As mentioned in the original post, I shot the empennage tips last week...same deal only it was 80 degrees and low humidity. They came out perfectly. There were no pin-holes to fill in the empennage tips and intersection fairings I shot that day so I briefly thought the blistering experienced this time was somehow related to the enormous number of pin-holes I filled in the wheel pants. Not so. Besides, the bumps also occured in places where no pin holes existed.

As for the wheel pants.....I removed the bumps by wet sanding them away with 2000 grit paper and they readily removed themselves but some surface luster was sacrificed in the process. Perhaps after the paint fully cures, I can buff the full brilliance back in. We'll see. If not, I'll just go ahead and try again. The good thing is my plane is not down while I'm making all these amateur mistakes on the wheel pants. But it will be nice to get them back on and get that 15 MPH back.

Rick Galati RV-6A "Darla"

OK, My Turn!

Those are some bad bumps there, Rick.
I didn't notice if you said that you painted the parts outside in the wind but if so, those could be Dandelion seeds or all sorts of pollen and the like.

However, from the picture (although not a great close up), I looks more to me that the bumps have a very globularish appearance (that's a technical term meaning "roundish" in appearance... forgive me if I sound like I'm trying to come across as a "pro" ).
And if that's the case, my first thought is that you might have gotten some water in the paint while spraying. The severe orange peel on the overall finish sort of agrees with this diagnosis as well.

The reason I say that is that most of us who paint at home typically use smaller size air compressors which work really hard trying to keep up which in turn promotes condensation in the tank. What you have there is exactly what water in the paint would look like.
However, I like the solvent popping idea as well because the swelling of bridged pin holes could look like that as well.

The best you can do at this point is to block sand some of it to a smooth finish (1500 with water and a sponge block) and just see what's there. If it's trash, you'll find the solid trash right away. If it's water, there'll be water (try popping one of those zits with a razor blade first just for fun). If it's solvent popping, you'll find little empty holes underneath.
Whatever it is, it's severe enough where you will not likely be able to just sand and polish it. Sorry, but it's looking like a repaint.

Several things

There could be several issues at work here. Moisture, contanmination, uncured primer etc...

You didn't mention the type and brand of paint.

Did you thoroughly clean the wheel pant before doing anything? If not you may not have gotten a good initial bond. I say this because you said the tip are okay. Different glass!!!!

You may not want to hear this but, start over!!! You'll pay time wise now but will be happier later.

I'd take them all the way down to bare glass. Scrub with soap and water and liberally wash with acetone.

If you don't want to go this route, wet sand the nits with 1200 wet until gone. Buff with a wool pad and 3M Perfect It 3000 followed by a foam pad and Finesse It II. (This is roughly $100 in materials)

I painted my plane in a professional booth with a base coat / Clear coat process. Even with extenisive prep and a professional booth there is still ocassional dust in the process. To get the finish desired it was necessary to wet sand the entire plane with 1200 wet then use the above buffing recommendation.

Good luck and let us know what you ended up doing.

Looks like (Seedlets)...

Looks like "seedlets" to me....Explanation of seedlets is, basically an overcatalyzation of the paint. This can and does happen in ALL cyanoacrolate catalyzed paints ( I have not shot your paint B 4, but I am very familiar with this and assume it is a CA paint...Don't ask me how I know this seedlet thing happens ) The only 2 real ways for for this to happen is over application, ie too thick of coats or too many coats applied too rapidly in too thick layers. Or.....too much catalyst. I am 95% certain this seedlet thing is what you have. It can be very confusing, cuz you can have a flawless looking finish, smooth, like plastic poured on then,,,WHAMMOOOO, in a couple of hours, it looks like you painted it at the beach! DUHOOO!!
To fix I have good news and bad news....First the bad...You will have to repaint those wheel pants, they will not sand/buff out to any degree of most people's satisfaction..... Good news, it is not that hard to sand and I would recommed no more course than 320 grit wet and dry, preferably IMHO 400 grit. As you wet sand and the water dries, you will see shiny unsanded areas (small) around each granule, if you have not sanded them all the way off.
I am sure it is NOT water entrapment or flashing. If it is solvent flashing, as you sand you will see a "crater" where the bump is, if this is the case, and, I HOPE IT IS NOT THE CASE, cuz if it is, your sanding chore just got a whhhoolleee lot harder as you try (swearing tons) to get the "crater" sanded all the way out.
Glen...Call if you need some encouragement/guidance . 561 670 6095
.
. PS...You may want to lower the paint viscosity slightly with a little more reducer , and/or lower your gun pressure some to lessen that amount of "orange peel" you are experiencing.....

Seedlets Suck

glenmthompson said:

Looks like "seedlets" to me....I am 95% certain this seedlet thing is what you have. It can be very confusing, cuz you can have a flawless looking finish, smooth, like plastic poured on then,,,WHAMMOOOO, in a couple of hours, it looks like you painted it at the beach! DUHOOO!!
To fix I have good news and bad news....First the bad...You will have to repaint those wheel pants, they will not sand/buff out to any degree of most people's satisfaction.........

Click to expand...

Thanks for the info Glen. I did wet sand those "seedlets" out easily and quickly enough with 2000 grit paper....thankfully...no craters were present. Still, some of the shine was lost in process. The funny thing is when I put the pants back on the airplane, almost everyone thinks they look just fine. Being located in the shadows under the airplane makes up for a lot of sins. But I know better. At first I though it might have been the high ambient humidity conditions present when I originally shot...it was raining outside at the time. I now tend to think I applied too much paint over too short a period of time. If any good came out of this, it is I lost my reluctance to shoot high quality professional paint......at least on small parts I can remove and bring home. It really is no big deal to repaint the wheel pants. Just a couple of hours work really. My friendly Sherwin-Williams tech rep told me to just make certain to remove all traces of shine from the (Acry-Glo) finish with 320 wet and try again. I"ll likely give it another go in the coming days....when the weather conditions are more agreeable. Right now it is rain, rain, rain.

P.S. The orange peel effect: I'll try your advice and both increase the reducer and decrease air pressure a bit on the next attempt!

Rick Galati RV-6A "Darla"

Rain effects on paint.

Rain has nothing to do with the "seedlet" factor. It will though, affect the flashing of solvents, drying times and in a few cases you will tend to get a "haze" if you use too fast of reducer that is caused by the paint drying so fast the surface cools rapidly causing condensation to form on paint film. Do not be afraid to paint when raining, just follow the store's instructions EXACTLY for painting in a high humidity environment.
Glen