Painting - painting concrete floors

I would like to paint my living room. I pulled up the carpet, sanded the floor. What's the next step? What kind of paint should be used, I want to create a marble effect.

This depends on the concrete. Was the carpet glued on, and is all the adhesive removed?

Some concretes are finished with a smooth, shiny surface. I prefer to etch these with muriatic acid first to promote adhesion.

If its rough concrete, and it is clean and dirt free, you could go ahead and prime it.

As for marble look, I can't help there, I'm not much of a faux guy.

You could simulate a "terrazzo" marble floor with a products from U Coat It. They have kits that will cover your floor with a seamless epoxy coating, then you toss in some colored chips to recreate the terrazzo look. Then comes a high gloss top coat, which seals it all in. I have used these products in a basement, garage and even on a front porch and I'm hooked! They hold up great and look even better. Check their website www.ucoatit.com, they ship right to your door. Hope this helps you.