Confused about mortar

[Ego Pizza]

Seeking some advice on mortar options for the dome...

From reading here it seems i have a choice on the mortar
 Either make my own homebrew as a lot have done
 Or buy ready made heat resistant mortar 

I was hoping to do the second - just from a time and ease point of view but can this be used for filling large gaps on the outside of the dome?  The cement from Kilnlinings  (- e.g.  kilnlinings.co.uk/firebrick-cements-other-cement/cement-dry-kldasc-to-be-mixed-with-water-25kg-bag-approx)   says it has a max thickness of 5mm

I was hoping to avoid as much brick cutting as i could  - especially in the lower courses, so would have big gaps - i guess around 20mm.  Is home brew the only solution for this?

Also what is castable refactory?   

Thanks in advance

Sam

[tim1989]

www.darleyfirebrick.com.au/castable-use.html
That link should help with your question about castable refactory. I've just ordered a bag of eBay to use to point the bigger gaps Inside my oven