I have concrete countertops in one bathroom and in my kitchen. I made the form for my kitchen countertop as I wanted to have drainboards on both sides of my under-mount sink and it didn't seem like my contractor was game for the details I desired.

I don't think sink cutouts are a big deal. I made the forms for mine. That's not where the tricks are, IMO.

I think it took a good bit of trial and error for my contractor to get good at color mixing, pouring, vibration, touch-up, polishing, and sealing. He had a steel table with big motor providing vibration. Without vibration to help the concrete settle in the form, there will be voids in face of countertop.

I'm DIY with respect to most everything, but think I'd get someone who is set-up for it to do it for me.

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

I built a long, curved outdoor concrete countertop for an outdoor kitchen a few years ago for a client. It turned out really well.

Cut outs are easy. I used rigid foam insulation the same thickness of the countertop, cut it to the size of the cut out I needed, and secured it to the form screws and a bit of adhesive. Because the foam is the same thickness as your form, when you pour the concrete you just screed right over it. Once the concrete was set, I just ripped the foam out, leaving a perfect void.

There are slightly different techniques you can use, but, the fundamentals are the same. It is a very labour intensive process but the steps are relatively simple, and there are tons of great youtube videos on the subject. You have many different options for finishing (colour, aggregate, level of polish, etc). We opted for a polished, cut aggregate finish, and it looked awesome. I wish I had pictures I could upload.

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Long Chile was a silly place.

I did my own kitchen and someone elses vanity.

For my kitchen I cast them in place, I put in a curve in one area with sheet steel. Ground it down with wet carbide sanding disks. The sinks are no big deal. The solid insulation works great for that. It would have been to big to turn over without a bunch of people.

For the vanity I cast upside down and turned it over. You have to fill in small bubble voids no matter what you do anyway so don't obsess over that. You just don't want big air pockets.

Color was black so just a bunch of carbon powder basically. Mixed a bunch of mica flake in but you have to look for it.

Just been using wax for the finish. 5 -7 years now.

DIY scale is somewhat advanced. You don't want it to be the 1st time you've mixed concrete or the 1st time you've built something for sure.

We did a garage countertop as an experiment. Turned out OK, but if I was going to do one where the appearance really mattered then I would do a 2 x 2 foot mockup first to make sure I had things right.

We used topping mix (so basically no aggregate) and laid in a 1/2 inch steel mesh, on top of a 3/4 inch plywood surface. I used a round-over edging trowel to do the front and side edges. Water-base flooring varathane to finish it IIRC, but epoxy would be ultimately more durable. With our finish we always have the option to get out some 100 grit wet-or-dry silicon carbide paper and just cut through it...

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Less is more.

i've researched this ad nauseam, yet never built anything. i suffer from analysis paralysis.
are you familiar with GFRC? glass fiber reinforced concrete? if/when i make something, i.e. small tabletop, coffee table, this is what i'll prob try first.

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