Bathroom reno drama, who’s at fault? Plumber or the Builder?

Background: We are doing a bathroom reno. We signed a contract with a builder, the duration of the project is 4 weeks, so far 4 weeks has passed, only demolition, restumping and plumbing have been completed. We have made two payments, firstly 10% deposit at the beginning of the project and the second payment (about 27%) after the demolition has finished. The next payment is due after the completion of waterproofing. We have been unable to obtain the invoices and receipts from the builder despite chased him at least five times verbally, over the phone, over text message and over email. We are very certain that he is doing another project concurrently as he only show up to our place about three hours last week.

Event: Last night around 7:40pm, right after my partner and I return home from the gym, the plumber showed up on our door and told us the builder has not paid him for the work he has done on 6th and 7th. He showed us the invoice he issued to the builder on 8th, so basically the builder has not made a payment to him in 10 days and he cannot reach the builder. The plumber asked us to pay him directly, we tried to explain to him that we have a contractual obligation to the builder so we cannot just pay the plumber, not without touch base with the builder first anyway. The plumber got extremely aggressive after we refused him, he was swearing, waiving his fists, threatening demolition the plumbing work he has done and report to the builder association and took us to VCAT etc, it was very shocking and scary.

After the plumber left we called the builder immediately and he said he has been sick over the Easter break, he also mentioned that he will sort out with the plumber. We followed up him on the invoices and receipts and he finally send these to us.

It was indeed extremely unpleasant to experience this. What the plumber did was unacceptable and we are not going to get bullied into paying him. As for the builder, now the reno project is overdue and we have no clue when it will finish as the builder just don’t show up or only show up a couple of hours per week, is there any more diplomatic way we can pressure him to finish asap? We don’t want to burn any bridges so he delivers a lousy job.

Any comments and suggestions are welcome, thank you very much in advance!