Can I use a wood sealer or polyurethane instead of the epoxy seal coat?

No. The seal coat has to be UltraClear Bar & Table Top Epoxy itself. Any other sealer, including general wood sealers, Waterlox, shellac and polyurethane, will still let air pass through the wood and rise into the flood coat as bubbles. Only the epoxy seals the surface well enough to stop that.

We don't sell a separate sealer product because you don't need one. The same Bar & Table Top Epoxy is used for both stages: brush on a thin seal coat first, then pour the flood coat 4 to 6 hours later. The instructions and tutorial videos walk through both steps.

Polyurethane isn't required before the epoxy either. You may see people putting several coats of poly on their wood before a flood pour, but poly doesn't act as the seal coat and the epoxy doesn't need it. The one time oil-based polyurethane comes into play is when the wood already has an incompatible finish on it: oil-based stain, oil-based paint, an oil finish, or water-based polyurethane (the epoxy only works over oil-based poly). In that case 3 coats of oil-based poly are applied to seal that finish and left to dry at least 24 hours, and the epoxy seal coat still goes on top.

UltraClear Bar & Table Top Epoxy: https://www.bestbartopepoxy.com/products/epoxy Instructions: https://cdn.shopify.com/s/files/1/0320/7168/0140/files/Epoxy-Instructions.pdf?v=1616443869 Tutorial videos: https://www.bestbartopepoxy.com/tutorial-videos/