You need to fix 6mm plywood to the floorboards first and then seal it with one coat of PVA adhesive mixed 50/50 with water, then another coat of undiluted PVA (see our project on PVA) then lay the tiles. If you lay them directly onto boards, especially boards with holes, the joints will very soon show through the tiles which will eventually crack in these places. Timber floors move a great deal, especially in bathrooms and every single little crack, split or holes will show through the tiles sooner or later.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!