neutral density - Which filter would I use for daytime lightning long exposure?

I'm new to the photography scene and although I managed to take a reasonable night time lightning strike on long exposure, during the daytime, I can't seem to get it right (too bright) and a friend told me to use an ND Filter. Is this something to consider and what type as my research led me to so many different types.

I am using a Canon 600D with the 18-55mm kit lens.