Hi, Lee Ann,

It's impossible to say what that is without a pretty good photo. Before and after would be even better but I doubt you'll have that.

You would do well to post this question (and a good photo) on "john Bridge Tile Forum" IMHO it is the best tile/masonry help forum on the net....lot's of smart folks there.

I agree with you....don't seal it 'til you get a handle on what it is and if the owner can live with it or not.

Dave S.