I'm hand-laminating over end-grain balsa on a deck and someone told me to seal the core first or it'll soak up loads of resin. That sounds like an extra step and more weight, so is sealing actually necessary or am I overthinking it?
Not overthinking it at all, because end-grain balsa is genuinely thirsty, and each of those little end-grain cells will happily wick resin straight up if you present a wet laminate to bare core. Left unmanaged that shows up two ways: a heavier panel than you planned, and a resin-starved skin where the resin you meant for the laminate has vanished into the core. A light sealing or priming coat, often a resin coat keyed to your laminating system, seals the cell mouths so uptake is controlled and predictable, and it also improves the bond by giving a tacky, consolidated surface to lay onto. The weight of a thin seal coat is far less than the resin an unsealed core would drink. Do check compatibility with your resin, whether epoxy or polyester, and follow the core supplier's guidance on the specific grade, since the ideal method varies by product.
Ask the Allbase team and we'll add the answer here for everyone.