Hi.
I've been working on carbon fibre skinning on some car parts.  Everything had went well until I put two last coats on before I start the fine sanding and polishing on the resin. 
But this time three are loads of crater like holes in the resin everywhere and quite a lit of air bubbles. The finish also has a white milky residue on the top layer. 

Is this contamination or an issue with the resin?

I did re-use the last paintbrush that was cleaned in paint thinners.  Could that be the issue or maybe some water residue on the part?

Thanks
Barry