I use a yellow/orange wax, which is relatively transparent. If mould starts to form under the wax, I can see it. This allows me to perform "key hole surgery", and cut a small hole in the wax, scrape the mould off, and rewax to seal the hole. Often, if a small hole forms in the first layer even your second coat will seem to flow around the hole. So, after the wax hardens a bit, scan the surface looking for holes. If you see one, blob some wax in and make sure you plug it. I've come to expect that I'll miss a few, and just keyhole until the mould stops showing up underneath. I don't mind doing it. I have a vac sealer, but still use wax as well.