Concrete Counter with Undermount Sink

I’m not sure what it was that made me decide to attempt this but I’m glad I did. When visiting my parents, I saw my first nice inside concrete counter which my dad made for their new downstairs bathroom. My friend also had one made for his outdoor barbecue but neither of them were exactly what I was envisioning. So off to see what the Google Monster had to provide.
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Here’s the finished product with my custom vanity that I decided I needed to make to go with the counter. I’ll go over each in this post and the next.
Most of the concrete counters I found either had a drop in sink or a built-in sink and if I was going to try this out I wanted to go for a undermount sink. Mostly because I think they look good and partly for challenge. Plus I’ve never had one and I wanted something nice. I didn’t find a whole bunch on Google about doing a concrete counter with an undermount sink so I decided to try it my way.

Bathroom-Counter-Plans

I decided that If I was going to attempt this I wanted to have some sort of formal design to follow. My research lead me to Google’s free SketchUp software. After watching the first few tutorials, measuring and modeling my original counter, I quickly put this 3D model together. I made it translucent so you could see the rebar and mesh on the insides. SketchUp is really nice because you can throw the measurements right on the print out to use it as a good plan.
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Here is the main form for my counter. Some people pour theirs into a basic form and use the top as.. well the top but I decided I would go this route with the melamine board so I could start off with a nice smooth surface. You’ll also see that I welded my rebar together but that was more because I wanted a reason to use my welder. I originally had a piece of styrofoam that I used for my sink cutout (see below) but I decided to redo the main piece and changed up a few things and went with the wood center. (I wish I would have gone back to the store for another piece of styrofoam..)
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This was right after pouring the counter, side splashes and test piece. I mentioned earlier that I did the main counter top piece twice. That’s because the first time I used a regular orbital sander to try to vibrate everything into place and that did not yield the desired results. When I pulled apart the form there were terrible air gaps everywhere. So many that I decided it would be best to start over. The second time I used a saws all reciprocating saw and of course no blade. I just put plastic over the end and it vibrated the whole table and sides quite nice. 
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Here is a few day’s after the concrete has fully set up in the form and under a sheet of plastic to help hold in moisture. The next step was to remove the center cut out and PVC pipes I used for the faucet holes. I regretted not going back to Home Depot to get some more foam because it was a pain cutting out the wood. Not terrible but the foam was much easier. (NOTE… If you use foam, make sure you put packing tape around the outside because it will yield much smoother results.)
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This picture was taken the day after I applied the acid stain. Before getting that far I sanded it all down with a 80 grit pad and my grinder and moved from there to the wet polisher and the diamond pads. After getting to 250 grit I stopped and filled in the tiny air bubbles with a slurry and rinsed and repeated twice. After I was satisfied with the lack of holes I applied the stain and put my rain coat back on and polished it up to 6000 grit.
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Here’s the day I devoted a few hours to polishing the counter. Even with the poncho rain coat I still ended up extremely wet.
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I get a lot of questions about this picture but from what I know, this is a standard way to mount an undermount sink. Basically slather the rim of the sink with some silicone or liquid nails and clamp it up. My sink also came with some bolts which I had a special way of using with some modified hardware.
This is also the first picture where it is sealed and actually looks like the final color. The only thing I applied after this was a wax.
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When trying to figure out how to increase the support of my undermount sink with bolts I decided I would put them into the concrete upside down. I originally decided I was going to put the bolts in before the cement cured but quickly decided against that. I didn’t want bolts to stick out while lugging the thing around to polish and stain it. I later decided that drilling holes and using a cement/metal epoxy would work best. So far it appears to be very strong and was much easier to deal with in the long run.
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Here’s one more shot of the final product after it’s been installed and waxed. If you want other views you’ll have to check out my custom vanity cabinet post.

Lessons Learned

  1. Seal all of the corners in the form with silicon. It will ensure smooth edges and you won’t lose any cement or moisture out of the bottom of the form.
  2. Always use styrofoam as a sink insert because it’s much easier to deal with. And it’s super cheap.
  3. Sand and then put on packing tape around the sink cutout to make sure you get nice smooth results.
  4. Use a reciprocating/sawsall to vibrate around the form and everything/everywhere you can. It will help settle everything and get all them air bubbles out.
  5. Get a multi pack of diamond sanding pads on ebay but spend the money to get a decent variable speed wet polisher. (I got a cheap one and regretted it.)
  6. Get a sample pack of stains and test them out with multiple coats on your sample piece. Most samples are more than enough to do a decent sized counter. I got mine from http://www.concretecamouflage.com/

4 Comments on Concrete Counter with Undermount Sink

  1. We're considering a concrete counter in one of our bathrooms. Having lived with this a while now, would you recommend it?

  2. I am still enjoying my concrete counter and get lots of comments on it. The one thing I almost kind of regret is making it so dark. We have such hard water in Arizona and the calcium in it shows up great on my dark counter.

    I'm considering doing a white concrete with blue glass aggregate for my next project.

    • I’ve used 5500psi Maximizer and 5000psi Sackrete concrete bags. I’ve been wanting to make my own mix of white concrete with glass aggregate but haven’t gotten back around to that project yet.

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