Did you ever get new flooring (wood, tile or carpet), and you had to shorten some doors for clearance? Here's how to redo a hollow-core door bottom when shortening leaves a gaping hole: You can easily replace the bottom rail with expanding foam insulation. Once the door is cut to the right length, clamp stiff boards on both sides of the bottom to prevent bulging when the foam expands inside. Once the core is refilled and the foam has dried, trim off any excess with a saw or utility knife; then sand and repaint to match, if you wish. Or leave it unfinished as it's on the bottom. Here's a tip for trimming doors to just the right height: With the door in place, take a piece of new flooring material along with any underlayment or padding you'll use and place it on the floor next to the door. Then, adding for clearance, make your mark after removing and trimming. And that's the On The House Tip for today.