My house was built in 1928and I've stripped the outside window sills down to paint that was probably applied in 1936 and seems to be welded on. All loose or flaking paint has been removed.This remaining paint is in fairly large sections. However, I imagine that being that stubborn it may not be necessary to remove it,nevertheless the uneven surface means that there are low spots of around 0.004"-0.008", about the depth of one or two sheets of A4 print paper, which will stand out like a sore thumb if I apply more paint. Is there any proprietary filler that can be easily spread over the sill that would create an even surface that could, if necessary, be sanded to blend with the existing surface without coming off or breaking away from the surface? Any advice would be very much appreciated.