What material is comonly used as insulator in laminations?
Assuming a stator's core construction is the same as a transformer's construction, this site has some good information, including these little snippets:

These steel transformer laminations vary in thickness’s from between 0.25mm to 0.5mm and as steel is a conductor, the laminations are electrically insulated from each other by a very thin coating of insulating varnish or by the use of an oxide layer on the surface.
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The laminations used in a transformer construction are very thin strips of insulated metal joined together to produce a solid but laminated core as we saw above. These laminations are insulated from each other by a coat of varnish or paper to increase the effective resistivity of the core thereby increasing the overall resistance to limit the flow of the eddy currents.

Varnish would work for both insulating and bonding to a certain extent, but better would be waxed paper, then mechanically clamp it all together, and encapsulate the whole thing in epoxy or varnish afterwards.