Hi Jophus,
If you mean 6mm cement backer boards then, as far as we are aware, these screws should be fine. However, if the board is being fitted in a damp environment e.g. bathroom, it may be better to use purpose-designed cement board screws, which will probably have superior corrosion-resistance.
Thanks for using Screwfix Q&A. JT
Answered by: JTremain
Date published: 2020-03-29