Need spray paint help.

[DaOld Man]

Wasnt sure where to post this. Its not arcade related or art, but I could use some advice from experienced painters on here.

I changed out my back door on the house, because the frame was rotting.
Put up new door (sub flooring and seal looked ok).
The old door had aluminum trim around the outside of the frame.
It was pained yellow to match yellow vinyl siding.
I decided to paint it white, since I think that looks better.
I flattened out a few dents and washed and sanded the trim.
When I painted it, all the trim looked good except for one piece.
Just in one spot it wrinkled up, about 2 inches in length. I wiped the spot where it wrinkled, then sprayed that spot again.
Next the paint wrinkled again around the just re-painted spot.
I had this same thing happen when I spray painted the back side of my photo booth monitor bezel. I had not seen this before with any spray paint.
I sanded the plexi bezel down and painted it again.
Has anyone else seen this behavior? Any idea what causes it?
Guess Im going to have to sand down the door trim and paint again.
First pic is the door trim, with the before and after second coat pointed out.
Second pic is the rattle can spray paint I used. Not a real expensive brand, but not a real cheap one either.
Appreciate any advice on what causes this and how I can prevent it again.
Thanks.

[yotsuya]

Use primer?

[DaOld Man]

I did, but this paint is supposed to have primer in it.

[DaOld Man]

I dont know if it has anything to do with it, but the can was getting very close to empty when this happened.
I cant remember for sure, but I think it was the same scenario with the spot that wrinkled up on the monitor bezel plexi, That was the same brand paint, just black instead of white.
Could it be some settled paint in the bottom of the can that is causing some kind of reaction?
I shook the can good before I started painting, and shook it between sprays.

[Ond]

This is usually due to a chemical reaction between the solvent in your new paint and the old paint.  It can  happen when you spray too soon after an initial coat when the first coat hasn't cured properly or it can happen when you paint with an enamel paint over an acrylic.  As paints cure they release chemicals which then react with fresh solvent to cause wrinkling.  To prevent this happening sand back old paint to base, prepare surface with primer and allow a few days to dry.  Then use the same type of paint to spray, only spray thin coats allowing a few minutes between each to dry off a bit.

Acrylic Primer with Acrylic Paint

Enamel primer with Enamel Paint

[DaOld Man]

Thanks OND (man Im glad you are back!)
I have no idea what the original paint was, but it could have been that I applied a second coat before the first was completely cured?
I bought a new can of the same paint, and tomorrow I plan to sand that piece down and try it again.

[jennifer]

  You will most likely have a bulls eye if you don't level your primer off before painting it again, usually with the thinner bomber can primers you will have to prime sand prime again... As for that wrinkling it is incompatibility between paints ,Or primer, or could be a contamination of some kind, most likely silicon if that's the case (usually found in spray oil, Turtle wax, or armorall products) *Example, if you just sand and paint the edges of your work area will start to lift again and you will just chase the problem.... Ond has the solution light spray let dry, light spray let dry, light spray let dry then paint wet, Is effective and does work.... A good sealer compatible with your paint on the area would also most likely lock it down.... In any case one the last coats Jenn would paint the whole thing again to blend it all together. (and the extra mil thickness wont hurt anything ).

[Zebidee]

Everything others have said is pretty sensible, and I suspect Jennifer could be right about the presence of silicon because it wont wash off with soap/water and traces could remain after sanding.

I wanted to add that when using spray can paint, I usually like to do a *very fine* sanding in between coats, using some very fine sandpaper that is so worn out to be nearly nothing but vaguely rough paper. Just enough sanding to roughen the surface a tiny bit. Do this for all coats except the final (and possibly penultimate coats if doing many light coats). This helps the paint stick securely and gives a very smooth result.

Another tip with spray cans, especially when the weather is cold or the can is close to empty - try immersing the can in warm water for a couple of minutes (or hold it under the warm water tap briefly if it keeps bobbing up in the water when nearly empty). Don't immerse/wet the nozzle. You can shake the can a couple of times to speed this up. The reason for doing this is that the paint won't stick properly if it is too cold (or too hot). This also helps you get the last little bit of paint out the can effectively before it splutters and becomes useless.

If the weather is quite cold you may also want to take this further and apply a heater to make sure the paint dries properly and/or without you having to wait many hours for it to dry.

[DaOld Man]

Thanks for the tips. I sanded it down until smooth, didnt take it down to bare metal.
I applied several light coats and I think it is going to be ok, but I can see the area that I wiped at the very first. Its not real noticeable, very faint, but I can see it so I know its there.
The piece of trim will go on the very top of the door (between door and storm door), so I think it will be ok, but I may try another couple light coats tomorrow. I just dont want to repeat what happened before, so I am a little shy.
I painted it out side in the open, and while last coat was drying, it started sprinkling rain, so I moved the piece inside. Will let it dry overnight and check it in the morning.

Zebidee: thanks for the tips. But weather here in Kentucky USA was around low 80's F yesterday, so i dont think cold was a problem. But maybe it was too hot?? Plus can was nearly empty so you may be on to something.

After this project is finished I may waste some paint on a piece of scrap to see if I can repeat that.
I would like to nail down exactly how I screwed it up so it dont happen again. I hate having to sand fresh paint off just cause I messed up.

[Zebidee]

Zebidee: thanks for the tips. But weather here in Kentucky USA was around low 80's F yesterday, so i dont think cold was a problem. But maybe it was too hot?? Plus can was nearly empty so you may be on to something.

Excess humidity can also be a problem.

If you spray indoors (eg garage) you can control your environment better. If possible, I like to make a little "spray booth" to further control environment factors and minimise dust/contamination (eg large cardboard boxes make a good spray booth for small stuff, sheets/old doors etc for bigger stuff). However, be aware that you need some ventilation for your own health. So, for example, lightly spray item in booth with mask on and garage door open, then close booth, exit garage and close garage door. Come back in 30-60 minutes.

The quality of rattle-can paints can vary a lot, some are better for certain surfaces than others (choose one designed for spraying metal), and the most expensive brand is not necessarily the best. Maybe try some different brands. Many light coats is always best, very light sand between coats.

Another thing to be aware of is that yellow paint in particular tends to "grin" through overlaid white paint (colour comes through), even after many layers have been applied. This effect is even more noticable if you paint over yellow paint on inside corners of a room/object (the physics: an inside corner effectively makes a "right-angle" or "corner reflector" which bounces light off each angle before it comes back to hit your retina, thus you see more up to 3 times more "yellow" grinning through). Don't know if you've had/noticed this issue.

[jdbailey1206]

I had this problem helping my wife with a wardrobe we painted for my daughter.  It happened when my wife went too heavy and too quick in certain areas not letting the paint dry adequatley in between coats.  Like everyone has stated just let it dry, sand down any heavy spots, and coat again.  I always use a sweeping motion about 9" away from what I'm painting to avoid any build up.  When it happened to us I just gave it a quick sand and repainted.  Not the end of the world.