I am going to build a retaining wall 50cm high and 11 metres long using concrete blocks wide side down. I will put in one control joint in the middle. Can the control joint just be left 'open' ie no fibre board inserted? The soil is, at the foundation level, heavy clay. I was advised that I should put reinforcing steel in the foundation due to shrinkage in the clay. Seems a bit OTT. Any advice? Finally how important is hardcore. For example would not leaving out the hardcore and making the footing deeper have the same effect. Cheers.