We are a GC on a project in which one of our subcontractors walks off the project and never finishes. We paid him on 10/10/17 and he worked a bit after that then stopped. He signed a partial unconditional lien waiver when he picked up payment. We have been notified now that his material supplier intends to put a lien on the project for invoices he did not pay. They expect us to pay them. Are we liable for them? According to our contract with the owner, we are required to keep the project free of any liens. But why have lien waivers if we have to pay anyways?