Sandstone Jamb mortar??

[scruffs]

Hi - just new to this site, I would like to know of the best mortar to use on the window jam of the early 1900s house we've just bought. The window jambs were boxed in between the window frames in the bay window and we didn't like the look of the wood. I took this off at the weekend to reveal the lovely sandstone. I would like to know what mortar/dye I can use to fill these sections?

Many thanks

 

[scruffs]

Also I've been notified that whatever I put on this Jamb must be able to breathe just as the sandstone does?

 

[^woody^]

It will look a mess just filled.

Fill it will foam, cover it will a upvc cover piece to match the frames.

If you want the sandstone effect, use a cement board such as aqua panel or masterboard and paint it sandstone colour.