We have a lot of professional painters on here and I’m sure they are already aware of this but I feel it is very important for the newer painters to understand what the real problem is here. I will try to explain as short and sweet as I can.
I have referred to dark colors in this post as being slower dry, not all dark colors but colors with a lot of black in their formula.
Black is made with Carbon; this comes to a paint company in power form. Most black paints the carbon will have been run through a grinder two to three times, the more its ground the blacker the black.
Now the problem is this, Carbon conduces electricity (you will never see a black power company truck!)
When you spray your basecoat the solvents dissipate in a ladder scale order, in your particular base you may have 2-3 different flash solvents and 1-3 mid grade solvents and a tail solvent. All these solvents have a different drop point so they will dissipate in an orderly fashion.
Now remember black conduces electricity so we have a problem with Dark blues some dark reds and a few yellows. As the solvents try to evaporate the static electricity is drawing the solvent back into the base – in short it’s fighting itself. For this reason black is you slowest drying color.
Now add in some other problems, such as spraying with a 1.5 tip, (to heavy) or high humidity (over 55%)
And now the solvent evaporation really slows down.
Or using to fast of a reducer in your base will skim the top surface to fast and also slow the rate of solvent evaporation.
You will also notice, I made reference to better clears having a different effect. Here are the symptoms.
In a good clear-such as a Hyper or semi hyper resin system or a normal urethane style clear.
Next morning after painted.
*Job was slick when done; now it looks orange peeled or wrinkled.
*Extreme die-back of gloss.
*Solvent pop.
*First coat of clear goes on good and second coat gets fish-eyes with in minutes of spraying.
These are not fish-eyes but extreme cases of solvent pop (solvent pop has about 4-5 different severity levels from looking like dirt in colors of white, black or grey to more advanced of looking like a full blown fish-eye.
Also I made reference to his only concern now is when the clear or base may lose adhesion.
Three things make clear peel.
1) Trapped solvent in base.
2) Letting base set to long before clearing (every company has their set amount of hours. 12-26 hours is the normal range).
3) Dry spraying of metallic to even out the metallic due to improper gun adjustment.
When ever you spray a black the flash times between coats should AT LEAST be doubled and same before applying clear.
I just made a black and the carbon is ground 7 times with different size shot, so its very tightly wrapped, the tech sheet calls for 60 minute flash time between coats.
The judge (Black) the black base was applied (3 coats) over two days and than sat overnight before I applied the clear. Air temp
was kept at 83 for four days and average metal temp was 75 degrees. with coldest metal (lower fenders and rockers) 72 degrees.
I used slow 885 reducer. (proper grade reducer would have been 870 but I like to go at least one grade slower under controlled conditions as this was.
May be overkill but this will be a $300,000 car and it must be perfect.
For further info on how solvents affect even the clarity or gloss level of the clear, see below article.
http://www.southernpolyurethanes.com/Creating the Perfect Paint Job.htm