Materials in an open fireplace

[Maboz]

I have a somewhat unusual fireplace, here are some pictures: http://imgur.com/a/c0rct

Now I want to build/cast/whatever you do to get a flat surface to place an insert stove on, which material and method would be the most suitable in your opinion?

My first thought was to remove the grate you see in pictures 2 and 3 and then just cast over the whole thing. Will need to repaint the whole thing anyway because of the rust you can see. Water came in when it rained so extremely that year and the ash drawer rusted, of course while we were on vacation so we couldn't dry the mess right away...

 

[MaxPax]

For the sake of simplicity, I would probably build with concrete blocks of appropriate thickness, using B-ruk, so I could level the surface with a few centimeters of mortar. Remove the grate and build in there as well, and finish with the outermost centimeter.

Welcome here, vetja!

 

[Maboz]

For simplicity's sake, I would probably build with lecablock of appropriate thickness, with B-ruk, so I could smooth out the surface with a centimeter of mortar. Remove the grate and build there as well, then coat the outermost centimeter.

Welcome here, vetja!

Thanks for the answer! I'll go with that option, then I hope to find some black heat-resistant paint that adheres to the mortar so I can paint the iron frame together with what I'm casting.