Hmm, this is odd.
I can't say I've ever applied Gunze Clear Flat over enamels, but I would have thought that the enamel should be unaffected if sufficiently cured. I have used H-20 over (Tamiya) acrylics without any issues.
The only thing I can think of is that the surface may not have been sufficiently clean before applying your enamel base coat. Applying the flat may have cooled the underlying paint enough to shrink and break adhesion on the underlying surface, manifesting as cracks.
Personally I've used H-20 over Tamiya acrylics without any problems and thin with methylated spirits..
somenewguy
I'll be respraying probably in a few hours, will Tamiya enamel flat have any side affects with humbrol enamel at all?
Tamiya doesn't have a clear flat in either the acrylic or enamel lines. If you are talking about bottled paint (X/XF series) what you are seeing as clear flat in the enamels may be the enamel equivalent of "Flat Base" (X-21) which is an additive to make gloss paints flat.
As far as I am aware, Tamiya only makes clear flat as a spray can (TS-80) which is a "synthetic lacquer". If you are referring to TS-80, after the enamel base coats are fully cured, apply in very light mist coats and allow to dry between applications - this shouldn't affect Humbrol enamels, but as they say, never say never.
Just as an aside, I've seen a few recent complaints about the decline in quality of Humbrol paints of late, you wouldn't be using the "Super Enamel" line would you?
PS: Bill, I've picked up a couple of pots of Tamiya enamels, but have not had occasion to try them yet.