For both I simply used the 5,000 psi mix of bagged concrete from Lowes or Home Depot. Added some pigmentation to the concrete when I mixed it with water. For the bathroom vanity I borrowed a friends polishing equipment and worked my way from 50 grit polishing pads to 3,000 grit pads for a shiny look. This was after squeegeeing in a slurry of colored cement to plug any micro air bubble holes for a more uniform finish.
For the window sill I wanted a more sandstone look. As soon as I peeled away the formwork (2-4 days after pouring) I scrubbed the fresh concrete with a stiff nylon brush and water. This loosened and washed away some of the "cream" and left a different more sandstone-like texture.
If one is going to do a concrete counter top be aware of the weight and how you build it. Plus you'll need to have shorter cabinets as the concrete shouldn't be any thinner than 2". Most counter tops are 3/4" thick with an extra 3/4" edge laminated on (so while it looks like it's 1 1/2" it's actually 3/4" as sitting directly over the cabinet tops). You can make the concrete as thick as you want, however.
Also, there are two methods of construction: pre-cast (what I did for both the vanity top and the window sill) or site cast (poured directly on top of the cabinets. You'll get the best, most uniform finish out of the pre-cast method as you can used factory smooth sheets of MDF, Malamine, etc. to build your form work out of. . . . just cast the piece upside down. With site cast you have to trowel off the top yourself, it tends to not be quiet as smooth and uniform, though perfectly servicable.
What dictates the method is how big of pieces you wan to cast. Concrete is heavy and so the pre-cast should be limited in size. My little 22" x 48" vanity top weighed about 140 lb.
For more info check out the
concreteexchange.com. And if you want to do this, YES, it's very worth BUYING Fu-Tung Cheng's book on Concrete Countertops. He's the guy that runs the site and has been doing this stuff for a while.
Oh, and a photo album from my concrete counter top project.