concrete over the fire brick dome

[sumu]

do you have to use the refractory morter over top of bricks or can you use portland cement for this. Then put the vermiculite insulation on then the stucco.

[david s]

As the portland breaks down from around 300C, this layer will presumably loose strength. However if the primary aim is for it to just add thermal mass, then no worries. Better to reduce the amount of portland and increase the proportion of lime, which is fireproof, although not as strong. If you want more strength then go for a refractory that contains calcium aluminate cement. This last option is the most expensive.