like taking coals to Newcastle

To do something redundant, frivolous, or unnecessary. Newcastle was once a major coal supplier. We definitely don't need to bring any toys when we go over their house—they have so many that bringing more would be like taking coals to Newcastle.

If you describe an action as being like taking coals to Newcastle or like carrying coals to Newcastle, you mean that you are giving things to someone or something that already has plenty of that thing. Sending guns to this region would be like taking coals to Newcastle. Note: You can also say that an action is like selling coals to Newcastle or simply talk about coals to Newcastle. Selling order and tidiness to Germans sounds like selling coals to Newcastle. More clothes for Nicola? Talk about coals to Newcastle! Note: You can also talk about a coals-to-Newcastle situation. Selling technology of this sort to Japan might seem a coals-to-Newcastle affair. Note: The city of Newcastle was the main centre of England's coal-mining industry for over 150 years.