Do Imirie Shims violate bee space and therefore encourage burr comb?
 
Imirie Shims definitely do increase the vertical space between frames, and
the bees will put some comb there (usually drone comb).  However, in my
experience it is easily scraped away.  Take advantage of the drone comb for
Varroa sampling.
 
W. G. Miller
Gaithersburg, MD