Is it preferable to use mortar to provide a smooth even level or some type of board?
The surface has old glue etc and some cracks and holes of course which we intend to grind down and fill.
We are extending the tiles over old mortar that has not been removed. Do we need to get rid of it?
(see photo)
Double brick wall is subject to some movement.
Many thanks for any advice or suggestions.
Regards
Diana