Well its not actually it is an alternative given to me by a guy who has built 3 wood fired ovens so far so i'll go with his idea as refactory cement can be quite expensive.
this is what he sent me. quote:" i did not use any refractory cement i used fireclay with a ratio of 5.1.2.1 five sand. 1 cement. 2 fireclay 1 hydrated lime."
