Do I need to put a pad underneath them to protect engineered hardwood flooring? And do I need to seal the seams so sweat cannot get in between them?

You don't have to put a pad or plastic sheet under our 3/8" PowerPlay Rubber Tiles to protect your hardwood flooring. These tiles will not stain or damage your hardwood if placed on top of it. If you are concerned, you can place a plastic sheet under your rubber tiles to protect the flooring underneath. These rubber tiles are the same thickness as what is found in most commercial gyms. So they will keep your subfloor safe from damage when dropping weights under normal conditions. You don't have to seal the seams of our interlocking rubber tiles as they interlock tightly and typically prevent any liquids from getting under your flooring. If you did have any concerns, you can seal the seams with our Seam Sealer glue or could place some Double Sided Tape over the seams.