Chart - FBR, page-227

Don't know the energy rating, but for years they've been saying that mortar has high thermal conductivity, and using adhesive greatly improves thermal efficiency (by 70%?). However, the adhesive is only on the top and bottom of the blocks. Back when they built a house by hand, using adhesive, the blocks had interlocking perpendicular joints. Nowadays they seem to leave vertical gaps, which helps the render attach. Not sure how much that compromises thermal insulation. Could air be better than mortar? You could always put insulation between the walls of a double brick structure.