After two years of pondering, I finally started a concrete counter-top. This will be going in a master bathroom. I have the mold construction complete. Next step is to radius off the corners and fill the small voids using caulk and/or bondo.
I’m ordering a new product from Lowes by Quikrete called “Countertop Mix”. (http://www.quikrete.com/productlines/CountertopMixPro.asp) I’ll need two 80lb bags costing about $11 each. I calculated the finished weight to be about 130 pounds.
Here is a great video on how I’m going to properly reinforce the concrete using #9 ladder wire.
I also need to decide on a color and technique. One technique I liked used a not-so-fluid mix of concrete, hand packed like a baseballs, then placed in the up-side-down mold. When complete, the underside looks like a typical concrete pour but the top side will have a bunch of voids that need to be filled with a complementary color concrete mix. This gives a marbling effect. I’ll post the link to this video if I find it again.
Here’s a great video about how to make concrete flow without adding more water. http://www.youtube.com/watch?v=naRoDinbbdc
You may notice I have a huge undercut in my mold. I’m not sure how I’m going to remove it after the pour. I’m experimenting with using water to break up the MDF. I’ve even considered burning the MDF out. I don’t have a good solution yet but I expect many hours with drills and chisels ahead.