The KBS isn't thin enough and so any trapped air wont rise up through the coat and leave a smooth surface. My guess is that you used a roller?

Yep. Although for the 2nd coat i used a fine brush thingy call a shur line from bunnings. Not sure if this is better? Would you suggest brushing over rolling?

I have basic spray gear i use for painting the cabs, just not sure i have the confidence with clear and spraying! If i did, what size tip would you recommend?

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