I don't know why, but anymore on the spray cans it says to topcoat within 30 minutes or wait 72 hours before top coating....
John
My understanding it has to do with the type and quality of the reducers (the part of the paint that evaporates) they use. Sort of like the difference between Lacquer thinner, paint thinner, gasoline, and kerosene. Set an ounce of each out in an open container (all the same size) and see which one is gone first.
Set the same solvent from 4 different suppliers out in the same test and you'll find they act different from each other as well.
Slower (and less pure) solvents that are not fully evaporated and 'cured' in the first coat reactivate and lift the pigment when the second coat is applied to soon. If applied within the first window the two coats melt into each other.
