Outer Dome with Concrete

[MadMarty911]

Looking to see if I am missing anything, it seems many builds have a perlcrete or vermicrete layer after adding insulation atop the firebrick or casted dome. Then followed with a coat of stucco.

I have done my curing fires and would like to have a 2" thick concrete layer with a waterproof/resistant coating with tile overtop.

Is there any reason I cannot do this? I've searched for days for a concrete outer dome but haven't found a sufficient answer.

I cast a 36" using homebrew at a 3:1:1:0.5 and have rockwool- and leftover ceramic fibre insulation made currently. Just ready to do the dome after my fires (max temp the insulation got to was 160F at 780* in the dome)

Thanks in advance !!

[david s]

The three reasons a vermicrete layers a good idea over blanket (ceramic or rockwool) layers are:
1. Adds more insulation a 10:1 mix is around as the equivalent insulation value as blanket.
2. Acts as a firm substrate to stucco against. Blanket is too springy and rockwool even worse.
3. Evens out lumps and bumps of the blanket and enables you to get back to a perfect hemi form.
2” thick stucco layer is ridiculously thick I use a 12-15mm thick layer applied in one coat, it’s like icing a cake, using a mix containing fibres for strength. Wet sponge when finished then wrap the whole oven in cling wrap to hold the moisture in that outer layer for a week to enhance its strength.

[MadMarty911]

Good to hear your thoughts, what if I cannot source vermiculite? Even finding perlite in any decent volume was difficult, hence why I was hoping to use concrete. Should I just use stucco instead? I am putting a waterproof mastic down to lay the tile with so wouldn't concrete work better than a stucco?
david s

[david s]

Both vermiculite and perlite are used in the building industry, but also agriculturally. Try hydroponics suppliers.
I actually use a 50/50 combination of both, finding a mix of fine vermiculite with medium perlite works better than either alone and the variation of grain size also helps, especially when making a really lean mix. Concrete or stucco just adds a lot of thermal mass the you don't really need on the outside layer. You just need sufficient strength to hold the insulation together and for it to be strong enough to resist fractures and cracks.