what will be the gst

Sir our business is of auto parts of car and jobwork on cars
we purchase car parts n aceesories in 18 or 28 % slab and sale it in same way
But we also do
... Jobwork on car... In jobwork we used to paint...the car..
N gst jobwork of cars is 18 %
N in this jobwork we use paint material which is consumed and comes in 18 or 28 %
But we make a bill of 18 % of jobwork
And claim the itc of paint

So i want to know.. Is it correct? Or what we have to pay extra gst on paint..
Or we have pay gst only on jobwork?