Q. Scott asks: Urgent! What is it meant by the term “grade of abrasive paper” and what is meant by the term “raising the grain”?
A. The “grade” (or grit) of abrasive paper (sandpaper) refers to the size of the abrasive particles in the sandpaper. Given the same number of passes and the same amount of pressure, paper with larger particles sands deeper (and rougher) than paper with smaller ones. A lower number indicates that the grade of the paper is used for rough sanding where a high number indicates the sandpaper is meant for finish sanding.
Generally speaking, 30-grit and 60-grit papers are used for rough sanding, 100-grit to 150-grit sandpaper is for medium sanding and 220-grit sandpaper is used for finish sanding.
Of course, this changes with the type of wood and whether the sanding is done by hand or with a machine. Sanding a soft wood with rough sandpaper could possibly tear the wood fibers (the grain). Sanding perpendicular to the wood fibers also could tear them. When the fibers tear they raise from the surface. Another way of causing the grain to raise is to over-wet wood.
The best way to determine what grit to use is to test-sand. Keep in mind that rough grits of sandpaper leave deep scratches, so start with the finer grits (150 to 220) and slowly work up to the rougher grades. Raising the grain is what painters must contend with after the first coat of paint is applied. At this point, and once the paint or varnish has dried, the first coat and the raised surface must be smoothed. The second coat of finish usually will not raise the grain. This is because the wood is protected from absorbing moisture by the previous coat.
Q. Bill asks: What is the best way to seal the garage door?
A. We assume you are referring to a sectional garage door rather than the tilt-type. Generally speaking, a high-quality sectional garage door that has been properly installed is reasonably weatherproof. But even the best doors can begin to leak after long use.
A simple fix would be to apply a 1-inch-wide strip of rubber to the inside surface of the door at each horizontal section joint — all the way from one side of the door to the other. Apply the strip to the upper section centered between it and the section below. A special rubber bottom can be purchased to fit the base of just about any garage door. For the sides of the opening — on the outside trim — attach old-fashioned weather-stripping for a conventional door. It’s the type with the round vinyl bead attached to a flat metal strip. If the door is wood, use staples or nails to attach your windproofing. If the door is a metal one, use half-inch, self-tapping screws. Once you have all the materials, you should be able to do the entire job in an afternoon.