Is all mild steel the same and does it matter?

[FJ12jagman]

I'm brand new to welding so if this is a particularly daft question please tell me gently....
I have acquired some new sheet mild steel off cuts from a local engineering firm. I think its coated with something as it doesn't rust and changes colour (more shiney) when attacked with a wire brush prior to welding. I have been using it for practice before tackling my rusty old mini. The sheet is 1mm thick, about the same as the mini panels.
Can I use this sheet to repair panels in my car (non-structural) or does it need to be a particular grade/quality, if there is such a thing?

 

[hotrodder]

Zintec maybe? It's electrolytically coated with (surprise, surprise) zinc and is kinda matt grey/blue. Pic of some here... http://www.mig-welding.co.uk/thin/stitch-weld.jpg. It's a popular choice as it doesn't go rusty before you've started work. There's various different grades and finishes of mild steel, pretty much anything that's commonly available will be fine to use just match the thickness as you've done.

 

[rtbcomp]

Grind it clean well back from where you're going to weld, as the zinc gives off poisonous fumes and contaminates the weld.

 

[pedrobedro]

I have used the coated steel from the local car spares shop and it will weld without any messing about and the coating is so thin it is negligible, not like the galvanising on pipes and other industrial coated stuff.

 

[FJ12jagman]

Many thanks fellas, most re-assuring and probably save me a fortune in pattern perts that I'll have to slice up anyway.