I've laid some 450x450 slabs on a bed of 9-1 grit sand and cement. The slabs have been laid 2 weeks. Trouble I have is I can lift the slabs straight off the bed. Is this normal? The sand has set solid so I was expecting the slabs to have set solid.
Using only grit/sharp sand will not allow the slabs to bond with the mix. Whenever I lay slabs I use a mix of sharp sand, soft (building) sand and cement to the ratio 3(or 4):2:1 and it works fine.
As you have found, although a little weak, your mix will set fairly solidly, but without any soft sand, it doesn't have the pliability to adhere to the slabs.
You might find that in time they will start to rock and any pointing will loosen allowing the rain and weather to affect the base. If you have layed a nice thick base it might not cause too much of a problem as lots of people prefer to lay slabs in a similar manner, albeit with a slightly stronger mix. I'm no expert in this field but have found that, having laid a fair few slabs over the years, the method I've suggested has worked best for me.
I'm sure someone here who is more experienced in the matter will be able to tell you for sure how well yours will stand up.
are the slabs restrained i.e are there kerbs around all edges? 450x450 slabs can be layed on a compacted sharp sand bed or 9:1 bed like yours but are layed close jointed with kiln dried sand joints. This type of bed is not so good for pointed joints.
You only need a stable base to stop the flags rocking it doesn't matter if they are bonded to it as long as they can not spread by having kerbs or the edge course layed on wet mortar or concrete.