Hardwood floors can last a lifetime or more, but only if they're properly glazed with protective gloss. This repels moisture and dirt and adds some durability to the wood itself against damage from hard objects. Varnish or shellac used to be common floor-glazing materials; today, you're usually better off using polyurethane gloss, which forms a tough, almost plastic-like seal over the surface. It's laid in thin layers, and it's important to buff each layer with very fine sandpaper before the new one is laid to help the next layer adhere.
Things You'll Need
Floor-grade polyurethane gloss
After your new floor is laid and stained (or your old one is sanded down and re-stained), thoroughly vacuum up the surface of all dust. Open and gently stir your polyurethane gloss, using your paint stick to gently pull the gloss up from the bottom of the can and swirl it around. Do it gently so no bubbles are formed.
Starting in a far corner of the room, away from the door, pour down a line of gloss near one wall, perpendicular to the direction of the floorboards and the same length as your lambswool applicator (generally, three or four feet).
Set the applicator in the gloss and push it to the wall, then pull it backward along the floorboards, going in the same direction as the boards. Pour more gloss as needed and continue glossing backward along the floor, going slowly to avoid creating bubbles. Continue until the whole floor is glossed.
Let the gloss dry overnight. Hand-buff the shiny surface with your 220-grit sandpaper, rubbing it just enough to take off the shine and leave the floor slightly dull. Vacuum up the dust.
Apply a second coat of gloss in the same manner as you did the first. Let it dry, buff it with 220-grit sandpaper, clean up the dust, and apply a third coat in the same manner. Don't sand the third coat, but let it remain shiny.
Ventilate the room when applying your gloss.