Hi, I have a problem on my front porch wall. Its front is ceramic tiles, and its side is concrete wall. (see photo attached). There is a big gap between the back of the ceramic tiles and the concrete wall, which I would like to fill and smooth it. I don't know what kind of material can do this job, concrete? mortar mix? or some other material that can fill and stay on this wall tight and firm? Appreciate any expert could give me some advice. Thank you.