<div>Here is my dilemma,

The slab of my extension was intentionally poured 55m below the top of the floor boards of my existing stumped home to allow for 35mm battons and 19 mm flooring. The slab was pretty good when initially done, well so I thought however after running a laser level across it yesterday the slab has high 7.5mm spots in one corner ( the worst) and on the other side It is spot on then falls away to -10mm down on the edge of the bottom plate. The average packing required under the battens would range between 3.5mm-6.5mm but on the most it is spot on the occasional High and low spots. The average batton length (of which I have 28, spaced at 450mm centers and are 9 meters in length.
One batten requires 13mm packing right at the end of the slab and tapers down to 1mm over 5 meters. Today I packed every fourth batten with masonite packers every 1.5 meters (where required). The hardest part is setting the laser level (get a self leveler).