Newbie Looking for Render Advice to Finish Vitcas Pompeii

[ploppyblobby]

How I wish I'd found this site before 

Have pretty much finished building the oven and just need to finish rendering the dome.
Vitcas recommend using either their heatproof cement (no thicker than 15mm they told me after I'd ladled it on  )  or screed.
But at £30-50 for 20kg am hoping for something cheaper and guess that means mixing it mesself. Have got a cement mixer and 6 bags of cement and was hoping someone would help me out.

Can you just use a regular render mix of 1 part cement to 4/5 sand or will the heat blow it?

Thanks in advance 

[ploppyblobby]

P.S. here's what the area we put the oven looked liked before and after

[ploppyblobby]

Took a fair amount of clearing, and practice burning.

[ploppyblobby]

So like an idiot i jumped right in and dug some footings.......................

[ploppyblobby]

But what we really needed were some meercats photos.app.goo.gl/yAwVDVaA3hMHBZYSA

[ploppyblobby]

So, had a load of rubble/hardcore that needed to go. What better place than in the base? 

[ploppyblobby]

Yeah, yeah. There's nowhere to put all your logs so that they can sit in the open air and the damp.

[devontiger]

pb, so if thats where you are up to now, its not too late to remedy.

Make an opening for the log store. Brick up a wall support inside, like a fire place.
Then carry on.
Like this.

[devontiger]

Or.............
Continue as you are, & built an extension.
Like this, a work surface & underneath a log store.