Is the resin supposed to be this thick, and how do I thin it?

Yes. The resin (Part A) is naturally much thicker than the hardener, and thicker still when it has been stored somewhere cool. That is standard and not a sign of anything wrong with the product. Cold, thick resin is harder to blend, holds onto air bubbles, and can come out of the bottle in lumps or blobs instead of a smooth stream.

The fix is heat. Stand the resin bottle in a bucket of hot tap water for 10 to 20 minutes before mixing. Warming it thins it out a lot, makes it easier to mix with the hardener, and helps bubbles rise out. Let both bottles come up to room temperature (75°F or warmer) before you mix, and use the epoxy in a room between 75°F and 80°F; if the product or the room is too cool, the mix stays thick and flows poorly. (UltraClear Deep Pour Epoxy is the exception and works in a cooler room, 60°F to 85°F.)

Thick resin is not a product defect, so it is not grounds for a replacement bottle. Our epoxy is made in batches of 10,000 gallons or more under ISO-9001 quality standards, so a single bad bottle is not a realistic cause; warming it is the solution.

If the epoxy is past its 1-year shelf life, warm it the same way, but test a small amount first to be sure it still cures properly.

Bar & Table Top Epoxy Instructions: https://cdn.shopify.com/s/files/1/0320/7168/0140/files/Epoxy-Instructions.pdf?v=1616443869 Art & Craft Epoxy Instructions: https://ultraclear.helpscoutdocs.com/article/864-art-craft-epoxy-instructions