Coloring concrete. ?

Thanks for the class and supporting Instructables and the do it yourselfers. I am going to be making a countertop for my home. I have a wet grinder and have made many practice molds/castings. My question is 2 parts

1. I am having trouble getting a good gray color from standard 5000psi bag mixes and one type of countertop bag mix. The 5000psi mixes have a gray/green color. Hard to explain. And the countertop mix is pretty ashy. Do you have suggestions on a mix, or do I need to buy a gray coloring from Mr. Roads or Mr. Chang.

2. I want to have the glasslike polished look to my countertop but without exposing agraget (if I can). Do I start with 400grit diamond pads and move up? Is there another method to polishing that I am just oblivious to?

Thanks again for the class. Sorry for the long message. Looking forward to lesson 4 tomorrow.

mikeasaurus8 months ago

Do the directions on the countertop mix advise adding additional types of concrete, why not just use the countertop mix? If you choose to color concrete it's best to mix the dye separately with water and portion it out for each batch of concrete before any mixing, that way you'll always have the right amount of colorant in between batches.

If you want a very polished surface and expose minimal aggregate then the best method is to cast upside down on a very smooth surface, like melamine or glass. This will likely have a very smooth finish that you might not need to do any finishing work on.

Casting against glass or shiny metal gets you a perfect gloss. If you don't want aggregate (rocks) showing, you start with a beauty layer, a mix of sand, cement and color chosen for appearance. This can be just a half inch thick. Let it start to set. Then pour in any old bagged mix. Don't even think about power tools!

A friend had a porch poured and the guys got a very smooth finish by repeatedly spreading/sprinkling dry cement on top then troweling it in. A bad choice for a porch, to slick, but would it work for a countertop?
ebjones3030 (author)  mikeasaurus8 months ago

1. The countertop mix was an all in one 40 or 60lb bag. Menards special stuff. No info on adding anything on the bag. It was gray but a little ashy. I was thinking I may have had water sitting under the piece i made in the mold. Heard that can cause funky coloring. Or maybe I just need to try the gray colorant and see how I like it.

2. I have only cast in melamine and it it very smooth. Though I'm not getting the shine I'm looking for. I have polished other pieces that almost glowed, but it exposed more aggregate that I wanted. Are my expectations unrealistic? WAAAAA! DIY can be so fun, but so frustrating. LOL