Strange paint issue
 

I painted my Jet boat yesterday and it looked great, went to check it out this morning and found these odd patches all over. I used urethane paint, sprayed three coats and all was well. I painted in a booth I bought at harbor freight, kept it at 65 degrees all night. I don’t know if it will sand and polish, will try tomorrow but if I have to re spray it I don’t want this to happen again! Anyone have any idea what could have caused this?

Re: Strange paint issue
 

It seems maybe something was gassing off under the paint?

Re: Strange paint issue
 

It does, they’re thousands of tiny bubbles, I just sanded a spot and they’re hollow, I’m going to sand it down tomorrow and try again.

Re: Strange paint issue
 

How much time between coats did you give it?...what does the pds say?
The paint I'm using says 15min minimum between coats

Re: Strange paint issue
 

About 20 minutes, supposed to be 15 but it was only about 65 degrees yesterday so I gave it an extra 5. Ive never had this issue before. My only guess is I put it on too thick, I had a couple runs and they looked like foam. I’m thinking it’s solvent pop, gonna sand it down until I see no more bubbles then sand the entire boat, give it a day to gas off then spray again.

Re: Strange paint issue
 

Urethane is the most finicky paint on flash times to eliminate solvent pop. I think the extra 5 should have been double the 15.. Temperature changes, insufficient air flow, all will alter your flash times.

Re: Strange paint issue
 

I’m gonna give it a half hour when I repaint. Going to sand until I see no sign of bubbles and try two more coats, maybe one if it covers well. It’s only about 15% of the boat that got the solvent pop, still going to sand the whole thing down, at least through the last coat. I’ve painted a lot of stuff but this is the first time this happened! Going to be more careful in the future!

Re: Strange paint issue
 

Urethane's need humidity and heat to dry. Most paint calculations are based on 70° and 50% humidity. If it was a low humidity day and you recoated too quickly or applied the paint to heavy bubbling will be the result. When the top dries before the bottom layers and bottom layers emit gas causing bubbling in the surface. So slow it down watch the humidity and heat and don't lay it on so heavy.I hope this helps

Re: Strange paint issue
 

Thanks! I will keep all that in mind!

Re: Strange paint issue
 

What temp reducer are you using? looks like You need to use a slower reducer to me

Re: Strange paint issue
 

I used a medium reducer, temp was right around 65 degrees.

Re: Strange paint issue
 

Well that’s not your problem, what brand paint are you using? Solvent pop usually happens in warm weather when a too fast of a reducer is used but a medium reducer at 65° Should not have done that even if you didn’t allow enough dry time between coats that usually ends up causing a runner or SAG

Re: Strange paint issue
 

It’s Martin Senior from Napa, I usually use Nason but it’s a 160 mile round trip to get it. I was able to sand all the solvent pop out, seems like it was in the last coat. It appeared in areas I think I sprayed too thick, the transom is only a foot away from the back wall of the portable garage/tent I’m spraying in. I know I was moving gun too slow back there trying not to drag the hose in pain or have gun hit the wall, had a pretty decent sag back there! Used a little hand plane to cut through it as it was pretty thick! The other areas were the very tip of the bow where I think I sprayed too much. Also appeared all down the center of the bow from the dash to the tip, I sprayed half the bow from edge to center then repeated it on other side, I should have continued from the wet center to the other edge. I’m really hoping it’s just a matter of to much paint!
I got it sanded down today, started at 220 then went through 320,400 and finished with 600, wet sanding each time. I did end up with a much flatter surface! I spoke with my friend who works at Napa and he tells me they’ve never had an issue like this, I’m really hoping it’s the amount of paint I applied, going to plan a better spray pattern tomorrow and take my time, don’t want to go through this again!
One other thing, I gut a hole for a box fan in the gable of the Garage/tent, up high and covered it with a filter to keep some positive pressure, I read that this can happen in down draft booths by drying out the top layer of paint preventing solvents from escaping, I tested fan today and don’t feel in air movement of any velocity so I don’t think that could be it. I open to any suggestions! Thanks!

Re: Strange paint issue
 

You say positive airflow does that mean you have air blowing into your booth as opposed to drawing the air out of the booth. Did you leave the fan run after you were done or did you turn the fan off ? I wait until all the overspray is gone and then I shut everything off and let it dry naturally

Re: Strange paint issue
 

Yes, I have fan and filter up near the peak of the booth blowing over the boat, I don’t feel a lot of air movement on the boat itself. I did this to keep mosquitoes and other flying bugs out. I also have a couple of plum trees blooming near the booth and the little flower petals had been blowing in under the fabric roll up door, the booth has a zipper on each side of the roll up door, I’ve been keeping one side zipped up and have the other side unzipped about half way to allow over spray out. I did leave the fan running for about two hours on high just to be sure nothing could fly or blow in, probably should have turned it to low.

Re: Strange paint issue
 

This was probably your problem that’s not how a booth works! suck the air out use a filter on in coming air. the air flowing through the booth for two hours dried the surface. By turning the fan of it let’s the solvents stay in the booth and let’s the paint dry evenly naturally

Re: Strange paint issue
 

I set it up to pull air through the filter and create positive pressure simply because it’s basically a tent with lots of seams and areas debris could enter if I tried to create a vacuum inside by having the fan on one end and the filter on the other. My paint was very clean, dust free when I sprayed, I’m going to run the fan slower when I spray today and turn it off when I’m not spraying, hopefully this makes a difference. Thanks for the suggestion!

I modeled it after this principle,
https://www.paint-booths.com/blog/paint-booth-air-flow/

Re: Strange paint issue
 

Had much better luck with paint yesterday, listened to advice and it made a big difference. Thanks!

Re: Strange paint issue
 

I got it fixed, turned out pretty good!

Re: Strange paint issue
 

Turned out great. Did you end up mixing your own paint? and does it now match the truck?

Re: Strange paint issue
 

I have a friend at NAPA, we matched it as close as we could

Re: Strange paint issue
 

Five degree rule. Paint is based off a seventy degree ideal spray temp for medium reducer and hardener. For every five degrees under seventy you double flash time. For every five degrees over you cut it in half. Put your first coat on a little skinny. Not dry but not with the same build you want on your second coat. You want the booth running as long as possible. If you turn off the booth the solvents will come out of the clear and lay back down on the clear.