How to Waterproof Bathroom Floorboards With Varnish

Updated April 17, 2017

Waterproofing wood floorboards is a crucial step in home maintenance, especially in a bathroom where moisture can cause mould to grow on your floor. You can use a simple urethane varnish over your treated floorboards to offer protection, and the clear varnish will ensure your wood stain still shows through. A few basic tools such as a paint roller and paint tray will help you finish the varnish application without having to employ a professional woodworker.

Sand the floors. Sanding down floors removes rough patches and splinters and ensures an even application of the stain and varnish.

Apply the wood stain to the floorboards with dust rags and let them dry. Apply a second coat if necessary and let them dry.

Attach an extension rod to the end of a paint roller so you can hold it at staff length without bending over while applying the varnish.

Pour a clear polyurethane varnish into a paint tray.

Apply the varnish to the floor by turning the roller in the paint tray, then rolling it over the floor. Apply a thin, even coat of varnish to the entire bathroom floor and let it dry before walking on the boards.


Start applying the varnish at the far corner of the bathroom and work back toward the entrance so you don't paint yourself into a corner.

Things You'll Need

  • Sandpaper
  • Wood stain
  • Rags
  • Polyurethane varnish
  • Paint tray
  • Roller brush
  • Extension rod
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