Dust mops will continue to pick up dust as long as they are relatively clean. There comes a point, however, when a dust mop can get so dirty that by using it, you will be spreading dirt around rather than picking it up. This is when a dust mop needs a good washing. In some cases, such as with sturdy synthetic-blend mops, you can simply put the mop head in the washing machine and run it through a gentle cycle. However, many mops--cotton mops, for instance--will start falling apart after a few times in the washing machine. To safely clean any dust mop, hand washing is preferable.
How to Clean Dirty Dust Mops
Fill a bucket with 1 to 2 gallons of warm water. Add laundry detergent and stir to mix.
Remove the dust mop head from the frame. Depending on the type of mop, this means you will either untie it or simply slip it off the metal frame.
Place the dust mop in the bucket of soapy warm water. Stir well with a dowel or large spoon and allow the mop head to soak for at least an hour.
Dump the old soapy water and add fresh warm water and detergent. Stir the dust mop in the cleaning solution and then allow it to soak again for a while.
Rinse the dust mop thoroughly in a sink under warm water. Follow with a cold rinsing and squeeze out any excess moisture. Hang to dry, preferably outdoors if the weather is warm enough.