What is the 'unfixed plant and materials problem'?

If you're a subcontractor and your contract says you only get paid when the materials are installed, one delay you didn't cause can turn you into the bank for the whole project. This is called the unfixed plant and materials problem. The idea is simple. You should be able to claim payment for materials as soon as they are delivered onto site or stored offsite, not weeks later when someone finally gets around to installing them. Because here's the trap. You can agree to be paid only when it's installed. Then, installation gets delayed for whatever reasons that are outside of your control, and you don't get paid, and it's not your fault at all. Meanwhile, you've already bought the materials, you've paid your suppliers, you've paid freight, you've paid labor to handle it. So now you're absorbing the cost and choking your own cash flow. So the mechanism is this: negotiate the clause so you can claim the delivered and stored materials early and stop funding the project for free. If you're waiting on install to get paid, you're not on progress payments, you are on hope.