You know according to the manufacturer the Storm blocks are pre-lapped and lapping is not recommended...just thought I'd mention that...
"Lapping, or sanding flat, the base of the block
Your Storm block has already been professionally machined and lapped flat for the primary CPU contact area defined as a 38x38mm (1.5.x1.5.) area in the middle of the base of the block. The satin-like dull reflective finish on the block.s base is intentional. A highly polished finish is not indicative of a flat contact area, just as a polished metal ball is highly reflective but absolutely is not flat. It is strongly recommended that you do not lap or polish the base-plate of the Storm water-block as you will make it less flat and degrade the quality of the CPU to water-block contact area.
Due to the purity of the copper used in the water block.s construction the copper portions of the block will tarnish quite quickly after being handled and exposed to the open air. If you notice excessive tarnishing then this may be quickly remedied by using some Brasso metal polish, or a scrub with a pot scourer cloth. DO NOT polish or scrub the base of the copper block where the CPU comes into contact with the water-block. "