rendaid is the best stuff to use its about 12 - 13 quid a bag but you should get about 8 metres from a bag, don't rake the joints out as this can cause the OCR to sink into the joints if you do want to use sbr then mix it into the OCR to form a slurry then cover the wall that way, if it's new concrete blockwork then you can render straight onto it, anything else and i strongly recommend rendaid or sbr