hI i JUST about mar hyde 2k surfacer primer with catalyst. I didn't read the primer before I bought it. It says on the direction 4 part primer, 1 part reducer, 1 part catalyst. Do we really need to add reducer to it? Or I can use it with just primer and catalyst.

Yes you need reducer. Paint/primer/clear always needs to be reduced, or its like spraying yogurt through a straw.

Then the catalyst is hardener....right?

Yes. Catalyst is technically a hardener.