Perlite insulation on a brick dome

[tarmac]

Is it ok to Perlite cement insulation straight onto a brick dome , I cant find any suitable insulating material in my area , I have no wish to retain heat for days but would like to have it so the dome is not hot to touch . Will this work or am I wasting my time ? I was going to use a 6:1 perlite mix - should I had fireclay to it ?

[david s]

Since around 2010, the current generation of ceramic fibre blanket became the default, the older generation was was considered a class 2 carcinogen. ie no tumours recored in humans but some in lab rats. For that reason and because the new generation stuff was really expensive I used not to use blanket, but only perlite or vermiculite. As the addition of cement reduces the insulating capacity drastically a really lean brew is best. From experience I've found a 10:1 is about as lean as I can go without it becoming too weak and too difficult to place. (see table)
The problem with wet verm or perlcrete against the dome is that if it is not completely dry the escaping steam will make it swell and crack. Especially if applied in a thick layer this water in deep is hard to get rid of. I found that applying a layer of around 35mm then allowing a week to dry before repeating another one or two more layers prevented this problem. Applying a blanket over the dome first creates an expansion joint and this problem doesn't occur. Now that the current generation of blanket has been exonerated as a carcinogen and the price now matches that of the older style, I use the stuff all time.