I have used LR20 Resin with SLC30 hardener. Between layers, any hollows were filled with microbaloons and resin mix and sanded flush.
After the 163 layers have cured. The lumps and bumps are water papered off and the whole lot smoothed off, then a final layer of 106 gram cloth is applied.
This final layer is then water papered as smooth as I can get it in preparation for spraying.