Sealing before grouting??

[SMG]

Hi,
I have laid Chrystancer Gris tiles on Marmox board in my shower / wet room. These tiles are like rough sandpaper, I want to use a flexy cement based grout but I`m a bit scared that the grout will "Stick" in the rough tile & I wont be able to clean it off. Do I need to seal the tile first?

Any help would be greatly appreciated.

 

[CBF]

if they are natural stone then yes i always seal before grouting & seal after

 

[SMG]

Thanks for that, No, they are a manufactured pressed tile from what I can see, its just they are so rough, like really rough sandpaper & I don't want to ruin the faces with grout.