The 59-year-old ‘Battleship’ star spent more than two hours ironing shirts for customers to help launch his sister Elizabeth’s new venture in Northern Ireland.
A source told The Sun newspaper: “Everyone did a double take when they they saw Liam ironing.
“No one expected to see a huge star like him doing the laundry.”
Meanwhile, the Catholic-raised actor – whose wife Natasha Richardson died in a skiing accident in 2009 - is considering becoming a Muslim after falling in love with the religion and its rituals during a trip to Istanbul in Turkey.
He explained: “The Call to Prayer happens five times a day and for the first week it drives you crazy, and then it just gets into your spirit and it’s the most beautiful, beautiful thing.
“There are 4,000 mosques in the city. Some are just stunning and it really makes me think about becoming a Muslim.
“I was reared a Catholic but I think every day we ask ourselves, not consciously, what are we doing on this planet? What’s it all about?
“I’m constantly reading books on God or the absence of God and atheism.”