They are permanent and go away as they are used to pop bloons, and they go away after each round. I dont understand what this is referring to... thanks.
Spike Factory spikes disappear after a while. Spikes R Us increases the time that these spikes will stay before disappearing. Here's my interpretation: let's say spikes from the Spike Factory disappear after 60 seconds. With the Specialty Building, they will disappear after 66 seconds instead.