dont think so mate with it only been a single block wall rain is always gonna come in
thats why a house has a 50mm cavity so when the rain dose come through it drops down
the cavity then on to the dpc tray then out of the weep holes .
dont think rendering will make a difference mate it will just soke through same as the block. but a might be wrong bud
did you put dpc (damp proof corse) on you bottom corse of block??