Queensland trainer Jamie McConachy has been disqualified for 18 months after being found guilty on a cobalt irregularity charge.

After a long-running inquiry, McConachy was last week found guilty of presenting Vandalised with an illegal cobalt reading following the horse's win in last year's Rockhampton Cup.

Stewards delayed issuing a penalty until they could give their reasons in writing and McConachy's lawyer Matt Tutt was told of the verdict on Monday night.

"I want time to digest what is in the sentence but we will be appealing within the five days' limit," Tutt said.

Chief steward Allan Reardon said his panel had taken into account McConachy's record and the trainer's detailed submissions but the serious nature of the rule breach warranted a disqualification.

McConachy is the second Queensland thoroughbred trainer to be disqualified for using cobalt after Glen Baker was banned for two years.

However, McConachy's charge was retrospective because his offence was committed before a national threshold was announced in January.

Baker has appealed his sentence and a decision is expected soon.

Stewards are set to open an inquiry on Thursday into cobalt irregularities found in horses trained by Toowoomba-based Rochelle Smith.