Artificial grass...how do you get the laying course flat?

[perky416]

Hi guys.
We are installing artificial grass in the garden to use as a putting green.

We used granite dust as a laying course. Flattened it with a rake, went over with the compactor 3 or 4 times.
Tampered down the raised edges caused by the compactor.
Aside from a number of loose surface stones it is solid.
Placed a straight edge on the surface and aside from a small number of dips only a few mm deep it seemed flat.

However when the grass was laid over the top and you run your hand over the surface it feels all bumpy underneath.

How on earth do you get the laying course dead flat?

Thanks

 

[conny]

Build an enclosure around the edge and compact down 3"-4" of sand maybe? The enclosure will help stop the sand shifting out of the edges.