Painting extended cast iron fire surround

[cad]

Can anyone offer me some advice?

I have recently had a tiled cast fire insert enlarged by having mild steel welded around the circumfrence.

Does anyone know what I can use to fill in the slight gap that exists between the cast iron and the mild steel prior to painting.

On the subjetc of painting, what products or methods are available to paint the mild steel so that it will blend in with the cast iron?

Many thanks.

 

[Nemesis]

I'm finding this hard to visualise.

Can you post a pic?

 

[essexbearhunter]

If it is on the outside of the cast iron then really the main problem is normally one of matching the texture rather than the finishing agent.

If both were (for example) vitrieous enamelled then (underlying texture set aside) the two would match fairly well.

Because it is far easier to burnish a surface than identically roughen it, if a "blackened bare metal" finish is required, it may be easier to burnish the (already smooth) steel and some details in the original to give the two visual cohesion.