It turned out to be a bit too hot during the heat wave, so I pushed my painting until late afternoon Friday. But paint I did. And made a mistake when mixing my paint, I think - so I'll have to sand the bumper smooth and repaint. Ah well.
Setup for paint went much like when I laid down primer. Put up the painting booth and wipe it down to remove dirt and paint dust. Wash & rinse the bumper, let it air dry then move it into the painting booth. Easy, but somewhat time-consuming. Oh, I took a picture of the stand I made to hold the rear bumper. The dowels sit in sharp curves or edges in the back side of the bumper, rather than somewhere else that might warp the polyurethane.
The next part was new - I had never used an HVLP gun before. First time for everything! I found a Youtube video on how to set up the HVLP gun for automotive paint, and the instructions worked well.
I have an old Husky 32 gallon air compressor that I bought a LONG time ago to use with impact tools, and it worked great for the job. (Haven't used the air compressor since I got a good electric impact tool, tho) I put the HVLP gun together and added a water separator. The air compressor lets me control the output pressure, so I didn't need a separate one at the gun. Verified no air leaks in the gun, so I was set.
Time to mix up the paint. I bought Dimension paint from Sherwin-Williams, and it requires reducer and hardener in a 4:2:1 ratio. Easy enough to do if you have some mixing cups specifically for mixing paint. I bought a nice kit off Amazon that had everything I needed. Sherwin-Williams recommends three coats of paint if you're color sanding, which I will do - so three coats it is. I wasn't sure how much paint I needed for three coats, so I started with a 14oz batch (4:2:1 in ounces is 7, so I doubled it).
Not-So-Pro-Tip: wear a N95 mask when mixing the paint. Even with California low-VOC paint, this stuff smells nasty! And don't mix it in the house, or it'll take a long time to air out. You'd think I'd have learned that by now...
Paint booth ready? CHECK
Bumper washed and ready? CHECK
HVLP gun and air compressor ready? CHECK
Paint mixed? CHECK
We are ready for paint? CHECK
Did we make a critical mistake? CHECK
The paint I mixed was going on thinner than I expected. It beaded up, but was really thin between the beads. It's possible I added too much thinner. Also got what I think are fish eyes, the paint just wasn't sticking to the primer in those spots. Didn't look like I had enough paint for a second coat (and I needed 3), so I mixed up another 14oz batch. Mixed some of the new batch with the remnants of the old, and this time it went on thick and even! I have no idea what changed, but I was happy. Sadly, the damage was done in the first coat. There was paint left over after the third coat, so I sprayed some more paint over a few spots I missed. Dumped out the rest of the paint left in the HVLP's paint cup - it was still about 1/4 full. Next time, I'll mix up 21oz instead of 28oz (14oz x 2) for a full bumper.
Some advice if you're going to do your own automotive paint - buy the right gear. This isn't like using spray paint - you ABSOLUTELY need a rebreather, and should get a one-piece disposable coverall and some goggles too. Automotive paint that uses a reducer and a hardener is much like a 2-part epoxy, and you do NOT want to breathe that stuff in. An N95 mask is not good enough. I have a rebreather, but I didn't have the rest - I just wore old clothes and shoes. Afterward, I didn't see any paint on my arms but after wiping my skin with acetone I got a lot of black paint off. And my glasses were covered in paint too. I had to rub them down several times with acetone to clean them up. The gear is cheap enough, like $50-$60 on Amazon and you won't have to scrub a bunch of paint off when you're done. I'll be buying a suit and goggles before I paint again.
Another note - that paint is STICKY! That's a good thing I guess, but I wasn't expecting my feet to keep sticking to the plastic floor of the painting booth! Here's a photo from the next day, showing how much paint got all over the floor. And that's not dust that will wipe off, it's permanent.
Finally, cleanup time. I ran some acetone through the HPLV gun to clean it out as per its instructions, then took off the nozzle and paint can to clean them too.
Here's a photo of the bumper the next day, with the paint nearly cured. This spot has most of the fish eyes. The surface was very bumpy right after painting, but it did level out quite a bit. Now, it's all orange peel. The WHOLE bumper. It'll have to be sanded smooth before I paint again. Still, not horrible for my first time using a HVLP gun. The imperfections CAN be fixed.
Sanding progresses. The process is the same as smoothing the primer coat: sand with 120/240/320/P600 grit. The Dimension paint I'm using recommends P600 as the final sanding grit to avoid fish eyes, so I use P600. I switch the direction of sanding when I go 'up' in grit, so: 120 horizontal; 240 vertical; 320 horizontal. I sanded P600 in swirls rather than a single direction. Since I was smoothing out orange peel, I needed to stop sanding as soon as the orange peel was gone. The top coat would be very thin at that point, and it would be easy to sand all the way through the top coat and into primer. Which I did in several places, but oh well. As usual, most of the work was done with 120 grit. Here's a pic of paint that's mostly sanded smooth. The black spots are low spots in the paint still.
As I mentioned before, I tape off edges on the bumper so I don't sand over them and round them off. This ends up taping off different 'panels' to sand at one time. I've finished sanding the panels I was working on, so it's time to tape off the other side of the edges and sand the remaining panels. I thought this was a nice contrast: orange peel versus smooth paint.
Wow, it's been almost a month since I last posted? Let's fix that. Painting time! Same drill - set up and fixed the painting booth, brought the bumper outside then washed it and dragged it inside the painting booth. This time, I was super careful to mix the paint right. I also bought a set of painter's coveralls and some goggles to go with my rebreather. Shot paint and...
Orange peel again. It's not so bad this time, but I obviously didn't fix the problem. Le sigh. However, after checking the paint the next day the orange peel didn't seem to be so bad as last time. And no solvent pop, so that's good. I'm going to try polishing this one, and see how it goes. If I sand through the top coat, I only lose a bit of sanding time.
Best guess on the orange peel problem, is that I'm not getting enough air to my spray gun so the paint isn't atomizing right. I read online that there's some pressure loss from the tank to the spray gun, and the longer the hose the more you lose. I have a 30 foot hose bolted to the top of my compressor, so that's possible. Gonna buy an air regulator to put on the spray gun, make sure I'm getting the 30 PSI to the spray gun that it says it needs.
EDIT: Paint's already gotten thin in a few spots. Looks like a third repaint is in my near future.
After some research and a lot of procrastination, I figured out why I was getting orange peel. I'll tell you what I learned, but I'm sure you're more interested in pictures. Try to ignore the ugly idiot holding the phone. Note the reflector indent on the right.
Not. Bad. But lost points for holding the phone vertical. Oh well.
Took these photos today, the day after painting. I'm sure I'll get better with more practice, but this paint is good enough to sand & polish.
Okay, let's rewind a bit. When we last left off way back in May, I had guessed that my orange peel issues were caused by not enough air pressure. Turns out I was right. I bought a pressure regulator and hooked everything up to see what the pressure drop was. You test the pressure on an HVLP paint gun when air is flowing through the gun. You do that by pulling the trigger halfway, which lets air flow without releasing paint. Of course, I'm testing so there's no paint in the gun; but I digress. So, I pull the trigger on the gun and the pressure read...2 PSI. When it should have been 30 PSI. That would be a problem! I cranked up the pressure regulator on the air tank until the regulator on the gun read 30 PSI, and the tank read 95 PSI. What? That's a lot of pressure loss. I was concerned that I wouldn't have enough air in the tank to spray a coat of paint, so I wanted to bring that number down. Some experimentation later, and the main problem was the cheap water separator I was using. Bought another one that claimed "high flow" and the tank read 65 PSI. Much better!
One of my tests was to remove the water separator and hook the gun (with the pressure regulator) directly to the tank - no hose. This is obviously useless for painting, but it should eliminate any and all pressure losses. I was able to drop the pressure from the tank down to 50 PSI when the gun showed 30 PSI. How do I have a 20 PSI loss between the tank and gun, with nothing but a coupler in between? I don't get that.
Alright, air pressure problem fixed; time to find a good day to paint. It's been really humid here on SoCal lately, around 80-90%, which is really unusual. And way to high to paint, even with a water separator. But the weather report showed the humidity was going to drop to 40% yesterday and today, then jump back up to the 80's. So I took that small window to paint the bumper. You saw the result above. I still need more practice, but I am getting better.
Had a weird problem with the paint gun after spraying the second coat. Paint started dribbling out the nozzle, and it wouldn't stop. Didn't dribble when spraying, fortunately; but still got a few drops on the paint. That's no worry, I can carefully sand those out. After I was done, I noticed that paint had drained backwards through the gun and into my new water separator, destroying it. Sigh. At least it wasn't too expensive. I have been cleaning the gun after each paint attempt, but clearly not good enough. I'm guessing the gun needs to be taken apart and cleaned better.
And that's the State of the Bumper. Next up: sanding and polishing.