Hi everyone,

I am hoping you can help me decide which is a better option or the pros and cons with the differences of some pre-cast kits I am looking at purchasing between.

kit 1 - 65mm pre-cast dome, 50mm ceramic blanket, 50mm perlite cement layer, then final thin render layer/waterproof finish.
Kit 2 - 100mm pre-cast dome, 50mm ceramic blanket, then a 30mm layer of premixed sand and cement with added builder clay for render. (no perlite)

I am thinking I will go with kit 2 but my question is, with kit 2 the final 30mm layer of render is not supplied in the kit, I have to purchase the mix and clay myself (but not worried about that) can I instead do a layer of perlite render then waterproof etc? My main thinking is to make this layer a bit lighter, and maybe bulking out the render with perlite might also make it cheaper.
Is one layer better than the other for insulation, the solid render vs perlite render?
Does this outer layer even matter given the 2nd dome is so much thicker than the 1st?
And I'm assuming that having a thicker dome will give me better heat retention for next day cooking of bread and slow cooking of roasts etc?

Also a lot of these kits in their finished photos on the websites etc have all the brick arch exposed and showing. Is there any reason why I cant extend whatever render finish I choose over the top and sides of the arch and only have the front of the brick face exposed? Just thinking I might like that better.

In case you are wondering what I intend to put it on, I am going to use blockwork to make a U shape with a single pillar in the middle (but open at the front so I can store wood underneath) and ready made 65mm reinforce concrete slab from local cement supplier. Both kits come with 50mm CaSi board. Base will be 1200mm by 1200mm.

Thanks for reading and look forward to your advice.