Hi all I've had a base completed for an extension 6x4m (raft upto subbase)I plan to finish the extension myself my first job is installing the floor slab. But the builders have left me with 4 courses of engineers built around the perimeter. I need to do an inner leaf of block work so I can put down the insulation board. And pour concrete and screed but I'm 325mm from subfloor to existing dpm. Therefore my blocks won't be level with the 4 courses I've been left. Can I run a row of engineers around sub base first then my block to achieve the optimum level to finish the slab.