  We recall a construction of Mackaay, Pan and Tubbenhauer of the algebras
$K^{\epsilon}$ which allow to understand the $sl_3$ homology for links in a
local way (i.e. for tangles). Then, by studying the combinatorics of the
Kuperberg bracket, we give a large family of non-elliptic webs whose associated
projective $K^{\epsilon}$-modules are indecomposable.
