There are two common reasons why hotcoats get air bubbles:1. Too much brushing - when hotcoating, you're "plowing" the resin around with the brush and the rolling resin captures a little air. The more rolling, the more aeration and it will get trapped in the resin.2. Too vigorous mixing. Same thing here. If you're whipping the resin while mixing in the hardener you're introducing air. In addition if you keep taking the mixing stick out of the mixing bucket and putting back in, each plunge will bring a little air with it...It is recommended you sand the current hot coat flat and re-coat to prevent water from wicking through the fiberglass. Essentially you'll be going a gloss coat, or second hot coat. No need to sand all the first hotcoat off, just level it out and scuff it up with 80 grit real quick.