Spray Paint Fogging

[Conway1979]

So, I am trying to figure out why my spray paint is fogging up after application. I just bought it yesterday from Auto Zone, Dupli-color perfect match. I have shaken the can for several minutes and hold the can back about 10 inches, the temperature is about 75 indoors where I am spraying. I have used the paint before when respraying the mirrors on my car, with no issue. Just curious who has run into this before and what did you do to solve the problem? The last time I had this issue, I think it was because it was too cold, but 75 degrees shouldn't be a problem. The only other thing I can think of is the propellant in the can is causing the issue. Thoughts would be great.

[Can-Con]

That's usually caused by humidity, and it doesn't take much either. 

I've found that if I hold the fogging part or body over a baseboard heater for a few minutes it'll clear up. Even just a hair dryer will work.

[Ace-Garageguy]

Duplicolor is usually lacquer. "Fogging", actually called "blushing" of lacquer is almost invariably caused by high humidity, as Steve says.

What happens is this: when the paint sprays out of the can and the pressure of the propellant drops as it expands into the atmosphere, the temperature of the propellant also drops. This chills the atomized paint enough that moisture in the atmosphere tends to condense on the surface of the fresh paint. The "blush" is simply moisture reacting with a component of the lacquer.

Evaporation of the thinners while the paint flash-dries in the first few seconds, with the resultant temperature drop caused by evaporation, will also cause blushing if the humidity is high enough.

The same thing will tend to happen if you spray warm paint on a cold body, or spray cold paint on a warm body.

It's usually only on the very surface, and will usually polish off very easily once the paint is dry.

It will also often go away if you shoot a coat of clear over it...but different materials work differently, so TEST on something other than a model you care about.

 

 

Edited November 26, 2016 by Ace-Garageguy

[Conway1979]

That would explain the blushing issue, I used to live in CA and didn't have this problem there. OH, definitely has humidity. 

[Can-Con]

That would explain the blushing issue, I used to live in CA and didn't have this problem there. OH, definitely has humidity. 

Yea, I googled Sheffield Lake OH and it said your humidity was about 62% at that time. That's definitely high enough to do it.

[Miatatom]

The same thing will tend to happen if you spray warm paint on a cold body, or spray cold paint on a warm body.

It's usually only on the very surface, and will usually polish off very easily once the paint is dry.

It will also often go away if you shoot a coat of clear over it...but different materials work differently, so TEST on something other than a model you care about.

With that logic in mind, I'm thinking that warming the body AND paint to the same temperature is ideally what you want to achieve. Is there an optimum temperature when doing this. My drying booth is variable and I'd like to play around with some experimentation ideas. I shoot decanted Tamiya lacquers through a Paasche H but would like to experiment some and also take another shot at acrylics. Any suggestions?

Edited November 27, 2016 by Miatatom

[astroracer]

Try heating the rattle can paint in hot water before spraying. Heating the paint will help with the humidity AND help the paint flow after spraying. I also set up a drying box before I spray paint. Just a big cardboard box with a clamp-on trouble lite in it. Turn on the lite before you spray so the box is already warm when you put the model in. I'll leave it for a couple of hours. If you shoot lacquer it will be dry enough to wet sand or continue painting if doing multiple colors.

Mark

[Ace-Garageguy]

With that logic in mind, I'm thinking that warming the body AND paint to the same temperature is ideally what you want to achieve. Is there an optimum temperature when doing this. My drying booth is variable and I'd like to play around with some experimentation ideas. I shoot decanted Tamiya lacquers through a Paasche H but would like to experiment some and also take another shot at acrylics. Any suggestions?

I personally find that around 75 to 80 F and humidity of 45% or lower to be about optimum for no-surprises results. Remarkably, we've had a really dry summer and fall so far in my neck of the woods this year...not at all as horribly humid as it usually is here.

When I was painting real cars, we always had a hygrometer in the shop and would tailor things like retarders (for lacquer) or reducer and hardener "speeds" to give us consistent results no matter what the weather was doing...within reason. In extremely hot and humid weather, I've had to go into the shop in the middle of the night to lay down decent urethane clears with no danger of solvent-popping.

You can't easily adjust most modeling paint products to maintain that sweet-spot, and controlling humidity is a bugger too. Even if you have a dehumidifier in your paint room, soon as you turn on the exhaust fan, you'll be sucking moist outside air into the room through every crack and crevice.

 

[Miatatom]

I personally find that around 75 to 80 F and humidity of 45% or lower to be about optimum for no-surprises results. Remarkably, we've had a really dry summer and fall so far in my neck of the woods this year...not at all as horribly humid as it usually is here.

When I was painting real cars, we always had a hygrometer in the shop and would tailor things like retarders (for lacquer) or reducer and hardener "speeds" to give us consistent results no matter what the weather was doing...within reason. In extremely hot and humid weather, I've had to go into the shop in the middle of the night to lay down decent urethane clears with no danger of solvent-popping.

You can't easily adjust most modeling paint products to maintain that sweet-spot, and controlling humidity is a bugger too. Even if you have a dehumidifier in your paint room, soon as you turn on the exhaust fan, you'll be sucking moist outside air into the room through every crack and crevice.

 

I'm just north of Chattanooga, TN about 15 miles and we are still in the extreme drought sector on the maps. Rain is expected on Monday through Wednesday and should bring 2-3", finally! We're closing in on 24" of rain deficit for 2016. With that said, my shop is along the back walls of the basement and fully enclosed.  It'll leak but it's not like there are large openings. I keep the room heated in the colder months and can maintain 75 degrees easily. I run a dehumidifier in the basement part closest to the outside door. Humidity levels stay a consistent 15% in the model shop. I'll be interested to see what some rain does. Do you think 15% is too dry?

[Art Anderson]

I'm just north of Chattanooga, TN about 15 miles and we are still in the extreme drought sector on the maps. Rain is expected on Monday through Wednesday and should bring 2-3", finally! We're closing in on 24" of rain deficit for 2016. With that said, my shop is along the back walls of the basement and fully enclosed.  It'll leak but it's not like there are large openings. I keep the room heated in the colder months and can maintain 75 degrees easily. I run a dehumidifier in the basement part closest to the outside door. Humidity levels stay a consistent 15% in the model shop. I'll be interested to see what some rain does. Do you think 15% is too dry?

Never heard of it being "too dry" to paint.

Art

[Miatatom]

Found out my humidity gauge is kaput. 15 sure sounded low.