If I lay fresh cement on old (50 or so years), will that interface be watertight?
If not, what do I need to do to make it so? Use some acid to etch away at the top layer of the old cement?
Use some sort of chemical mixed into the new cement?
Paint on some sort of chemical to the old cement? If this, do I wait til it has dried to add the new cement, or paint it on and pour the new cement right away?
Thanks for any help.