Abstract: There are disclosed high temperature refractory mixes especially adapted for relining and resizing chimney flues, comprising from 65 to 70 weight percent of portland cement, from 21 to 25 weight percent of volcanic glass, from 6 to 10 weight percent of microsilica, from 0.05 to 0.12 weight percent of at least one air entraining agent and from 0.5 to 1.0 weight percent of at least one plasticizer.