Overtime in Grounded, your weapons slowly degrade and break down. They don’t become worse the more you use them, but there’s a small meter next to several of your weapons and tools that show how much longer they have until they break. When they break, an item doesn’t leave your inventory, forcing you to make a new one. Instead, you can choose to repair it so you can continue using it. To do that, you need to make use of a material that takes a bit of effort to locate, but it could save you from remaking your favorite weapon from scratch.
You need to make sure you have quartzite in your inventory to repair your tools or weapons. The resource is commonly found underground, and you can harvest it with level 1 hammer. A great place to mine for it is in the anthill to the northwest of the first field station or near a small cave where you had to investigate what was weakening the laser when attempting to repair the mysterious objective. Once you have that in your inventory right-click the tool or item you want and fix it.
The amount of quartzite you need to repair a weapon or tool depends on its tier. It also doesn’t matter if you’ve used it three times and has a bit of degrade or completely destroyed. Both appear to use the same amount of quartzite, so you’re better off waiting until it’s completely destroyed until you repair it. It’s not bad idea to carry around a little quartzite when exploring the garden to make sure you don’t find yourself about to fight a spider and your mint mallet breaks.