Honestly there's no way that you'll stress Couch grass at all, only if you tip petrol on it will it suffer, so don't hesitate to put more sand over the top. I will say though it would be best to keep it damp until the grass comes through it and stabilises the surface.
Cheers, BB.
I live a 24 Hour lifestyle, but every now and again I seem to fall asleep, well at least that's what my wife tells me.
