Glue Supply Depot is a Specialty Building for the Glue Gunner. It was released on July 5th. It costs 2500 to completely upgrade the Specialty Building (3750 in Mobile).
Compared to the Ice Fortress, the Glue Gunner is good on the aspect of directly slowing down bloons and getting the expensive corrosive path-1 upgrades or getting maximum glue power. The Ice Fortress, however, allows Ice Monkeys to freeze for longer (tier-2) and freeze all types (tier-3). Both Specialty Buildings are related to slowing to avoid overuse of combinations of Ice Monkeys and Glue Gunners. Despite this, a 2/2 Ice Monkey could still be used in conjunction with a 2+/2+ Glue Gunner and still make pretty good bloon stopping.
Glue splats last for ~70 seconds if left undisturbed, but will disappear immediately when a round ends.
When Bloons leave Glue on the track with level 3, the Glue is always yellow even if a Bloon Dissolver or Bloon Liquefier shot it. It Dissolves/Liquefies what passes through it though.
In Bloons TD 5 Mobile, the glue that gets left on the track (Tier 3 upgrade) is not harmful even with path 1 tier 2+ upgrades. This change is "reverted" in BTD5 Steam.
1 splat of glue can glue 1 bloon, making it less effective than people would think.
The glue only splatters when a Red Bloon (from any bloon, though) pops.
There is a 50% probability (measured in BTD5) to drop a puddle when indivisible bloon is popped. When glued Rainbow Bloon/Ceramic Bloon offsprings are all popped, the statistical expectation of puddles generated is not 4 * 0.5 = 2 but still 0.5... Only first zebra bloon inherit oportunity to make a puddle, similary the first white bloon from zebra. The same way for Zebra Bloon and Lead Bloon statistical expectation of puddles dropped is 0.5... So, glue can not propagate by popping Rainbow Bloons