They claimed he breached the terms of his employment agreement, causing the company loss, and he failed to act in good faith.
Jones told the authority his actions were authorised and that the scrap metal did not belong to the company.
But the authority has ruled in favour of CMBL with a recently released decision revealing how the Gillings discovered what was happening.
In early July 2021, Kathryn Gilling noted the mobile account connected to Jones' work phone showed "significant" data usage over the weekends.
He handed over his phone so his bosses could investigate the use of data.
"On examination, text messages contained on the phone indicated use that appeared to be unauthorised and actions Mr Jones had taken which were unauthorised," the decision said.
Jones, who had worked at CMBL since 2014, had sent messages such as "…clean[ed] up the ally [aluminium] rack and t[aken] all the hidden off cuts lol".
The decision said other messages revealed he had been using the workshop and company materials for his own "cash jobs", had distributed private information of an employee drug test result, a job offer made by CMBL and pages of Peter Gilling's diary, and that he had made disparaging remarks about Peter to a supplier.
On July 12, 2021, CMBL wrote to Jones raising matters to be investigated but the next day he resigned.
Jones did not dispute he had sent the messages but told the authority the aluminium did not belong to CMBL, any personal work was done in his own time using only scrap materials, and that he was exercising freedom of speech.
The authority ruled that Jones had breached the terms of his employment agreement and breached the statutory duty of good faith.
"I am satisfied the aluminium sold by Mr Jones is more likely than not to have been the property of CMBL because the unauthorised selling of CMBL's 'ally' is in a text message he sent, the aluminium is the type of material used in the CMBL workshop, its storage and transportation involved CMBL resources, and the evidence of its origin elsewhere is not strong," ERA member Marija Urlich wrote.
"Further, I am satisfied Mr Jones sold the aluminium while he was employed by CMBL and he did not seek CMBL's permission to do so or permission to use its vehicle for its transportation."
Urlich ordered Jones to pay CMBL $1393 for the metal and $4000 in damages for the breaches of his employment agreement.
Kathryn Gilling welcomed the decision.
"We're pleased with what has happened," she told Open Justice.
"He so blatantly betrayed our trust that we just couldn't let it lie."
Open Justice was not able to contact Jones for comment.