Fireplace advice

[Tiggi]

I'm new to this so please bare with me!

I have opened up my fireplace and am left with bare bricks inside the fireplace. Its a little uneven with some small gaps...so would I be able to cement over with lime mortar to give a smoother finish and seal it and then use the recommended heat spray so I can use as an open fire.
Or is fitting a fire back a better idea?

 

[noseall]

It depends upon aesthetics.

There is a large visual difference between a pre-cast fireback and a rendered opening though the fireback would be more stable.

 

[Alastairreid]

http://www.travisperkins.co.uk/c/plumbing-and-heating/fire-cement-rapid-setting-cements/961017