Final answer:
To shape a weak natural nail, a fine-grit file of 240 grit or higher should be used to prevent damage. Gently file in one direction and opt for a padded emery board or a glass nail file instead of a metal one.
Step-by-step explanation:
To shape a weak natural nail, it's important to use a file that is gentle to prevent any further damage. A fine-grit file, typically in the range of 240 grit or higher, is recommended for weak or brittle nails. These types of files are abrasive enough to shape the nail without causing splintering or cracks.
Start by gently filing in one direction from the edge to the center of the nail, rather than a sawing back-and-forth motion which can cause more damage. Remember to file the nail into your desired shape with gentle, careful strokes, focusing on maintaining the integrity of the natural nail. It's also advisable to avoid metal files, as these can be too harsh for weak nails; instead, opt for a padded emery board or a glass nail file that creates a smooth finish.