in the old days to slow down plaster we would put milk in the mix and to speed it up we would p**s in it and you know what they both worked (but the plaster would smell a bit of cheese for the milk one and would smell of you know what for the other). But what you could do is pva the artex first then coat in a thin coat of thistle bonding and then next day skim as normal it will suck for a minute or two then once laid in it will not suck and should be a p**s to trowel up.