The chief reason for chalk line failure is water damage. If your chalk line gets wet, it can ruin the chalk powder and make it unusable. Moisture can also weaken the string line, making it prone to breaking. Storing your chalk line in a cool, dry place should help to keep it in excellent working order.
Drying out
String line
If your string line has gotten wet, unwind it from its reel, lay it out in a place free from moisture and allow it to dry before using it again.
Powder
If your chalk powder becomes damp, you will have to empty the box, dry any residual moisture and refill it.
Replacing a string line
Your chalk line is probably going to see a lot of day-to-day use so there may come a time when you need to replace the line. Lines can be purchased separately as single specific lengths or as larger spools from which you can measure and cut many lengths. For more information, see the page entitled: How to replace a chalk line’s string