Now if your grout is a dark color then it can be advantageous to apply a sealer before grouting to keep the grout color from absorbing into the edges and discoloring the marble.
Carrara marble sealing before grouting.
I prefer to seal mine before grouting.
Hi guys i have a stone tiler fixing some carrara bianco in my bathroom.
Carrara marble needs sealed.
Those couple of tiles must have been a bit more porous than the rest.
The edges of the tile are much more absorbent and if the grout color is dark then the dark water from the grout will absorb into the edges of the tile and create a picture frame stain.
I just installed marble tile in an entryway dark green with dark grout.
You ll have to replace those to make it look even.
Then i used a grouting sponge to wipe off any excess.
I used this sealer and just put it in a spray bottle and sprayed three coats on the ungrouted tile.
Because marble is a natural stone and will absorb color you need to seal them before you grout to prevent the grout from discoloring the tile.
I am using a grout from a store i never used before and they told me to seal the marble before grouting because the grout might stain the tile.
If these deposits are close enough to the surface they can be oxidized by water absorbed during a shower creating a rust stains.
My guess is it wasn t sealed so a couple tiles soaked in some grout darkening them.