Our neighbors are having their kitchen and most of the first floor remodeled. Part of this will eventually include their laundry/mudroom. During a driveway discussion they expressed interest in a concrete utility tub, but the best price they could find was well over $1,000. I was, of course, intrigued. So I started making a concrete utility sink for the neighbors! We found a really nice looking example to base it off of, collected some basic measurements and I got to work.
I had plenty of melamine left over from the basement bathroom sink to build the mold.
Although the inside of the sink is basically a rectangular cube, it needed to slope to the drain somehow. For this I used a thin piece of backer board and bowed it.
The inside form received multiple coats of drywall mud sanded smooth then I sprayed the whole thing with Plasti Dip. This gave a really nice, waterproof finished surface.
I created the drain shape by melting a 3D printed flange to some 3 inch PVC. This worked great. The really difficult part of this whole thing ended up being getting the mold caulked. The deep but narrow sides meant I couldn’t fit my hand in there or even manipulate a tool in there. If I did come up with a way to smooth the caulk, how would I clean up the excess???
I took the bottom off the mold with the inside piece still attached and caulked all the available joints. I then globbed some caulk where the bottom of the mold would meet the sides and hoped for the best. This area represented the outside corner of the finished sink, probably the easiest to grind/polish/repair if needed.
With everything assembled and the caulk cured, I mixed up two 80lbs bags of regular old quikrete. Plopping in a few shovel fulls, I focused on vibrating the mix into the area where the faucet would be….it was kind of a nook down under at the back of the form. When I finally got a burp and the mix sunk down under I began filling the rest of the mold.
Out of the Mold
After a good 7-10 days of curing, I started pulling the mold apart. It came off easily except for the inside form. I really need to start waxing those parts…
Eventually it all came out and I was able to start polishing.
All of the vertical sides of this one ended up with a neat drippy pattern, I assume this is from the hour plus of vibrating all the bubbles out of the wet concrete.
It turned out that the difference in color tones also related to a difference in surface finish. The wet polisher was taking a long time to smooth out the rough spots so I jumped to the grinding cup. Some VERY careful grinding made quick work getting to a uniform surface.
Several hours of wet polishing and boom!!
I love the way it looks wet. Looks good dry too. Once it’s sealed it will be somewhere in between the wet and dry look. Similar color to the wet without the gloss.
Sealed and on the stand
With the full 28 days of curing passed I was able to seal the sink. I also spent some time building a stand for it. The stand had to be a little odd shaped due to a lot of supply and drain lines in that spot. It came together quick with only dado joints and glue. The stand will get a final sanding just prior to stain. Also need to cut a hole for the faucet once one is selected. Then install!