Although the heat of heated bed in your Ultimaker 2 Extended already takes care of adhesion of your print to the glass plate, this is not always enough. In some cases it is desired to also use glue on the glass plate, for even better adhesion.
When to use glue?
The use of glue usually depends on the material you’re using and the size and shape of the model.
For ABS and CPE we recommend to always use glue, because these materials have more “warping”. Warping basically happens because of the properties of the plastic. Plastics have the tendency to shrink when cooling down fast (some plastics more than others), which could eventually lead to your print curling up (at the corners). Since ABS and CPE have a relatively big shrinkage you will need glue to prevent it from warping.
PLA on the other hand, has a much lower shrinkage and thus less warping. Because of this it’s often possible to print PLA directly on the glass plate, without glue. In this case you need to make sure that the glass plate is completely free from dust and oil though, because plastic won’t stick well to a greasy surface. There are however situations in which glue on the glass plate is desired. If you want to print a model that has a big footprint, or with very thin parts at the bottom it’s advised to use glue to prevent it from getting loose.
How to use?
The glue stick that was delivered with your Ultimaker 2 Extended can be used for the glass plate. Therefore simply put a thin, even layer of glue on the glass plate. It’s only necessary to apply glue to the print area.
Tip: To better distribute the glue over the platform you can use a damp cloth. This way a very thin layer of glue will be left on the glass plate.