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This Old Crack House

From log house to farmhouse. Farmhouse to townhouse. Townhouse to apartment house. Apartment house to crack house. Crack house to our house. Our house to our home.

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Wednesday, October 17, 2007

Making a Concrete Sink (Part 1)

When you tell people you are making a concrete sink for the bathroom, they look at you with a strange expression. This is because when I say concrete they envision the sidewalk outside their house. So, don't look at me with that strange expression any longer. I am going to take you on a journey with me as I attempt to make a piece of art for our bathroom.

Half the problem with making a sink is figuring out how to make a mold. You have to be able to picture the finished item in your mind and also how it would look in a reverse form. The materials used for our mold are simple pieces of left over melamine board and 1 X 2 pieces of lumber, packing tape and screws.

My first attempt at making the sink didn't work and I can walk you through the process and explain why. When I made it, I quite expected certain elements not to work so I wasn't going to be upset with the end result if it failed. As it turned out in the end the sink would not have sat properly in the allotted space and we didn't like the way the counter top turned out so we would not have used it.

The things I thought would be a problem were the depression for the drain and the way the color would turn out. I also had some worries about dismantling the mold which ended up being my biggest problem. I used a bag of cement that had been sitting on the floor in the kitchen for two years also. I didn't know if it would actually be much good but with so many "ifs" hovering over the project I decided to use it instead of buying a fresh bag and being disappointed with the result.

When you design a mold that produces anything but a completely flat surface you have to anticipate being able to dismantle it or remove any build-outs with ease. I used a combination of melamine and Masonite panelling for the basin build out but managed to place the screws on the concrete side of the mold which would make their removal impossible. I caught this early on and thought I could solve the problem by not screwing the back part of the build out to the sides. I also anticipated that pulling the rest of the build out from the concrete would be easy. That was wrong. I didn't take pictures of the mold as I built it but here is the entire thing after the concrete was poured.

I have two concrete dyes at the house. Black and terracotta. I decided to see if I could create a marbled effect in the concrete and so I mixed two batches of different colored concrete and placed them in the mold in such a way as to create a mottled pattern. I had no idea if this would work and whether the entire thing would turn out as a brown mess. I have one other problem, that is polishing the inside of the sink basin. My variable speed grinder and polishing pads won't have enough room to work in a narrow basin and this problem is why I opened up my mold after only a few days because I figured that I could use "wet and dry" paper on the basin interior while the concrete was still relatively soft.
Getting the exterior part of the mold apart was easy as this picture shows in part

When it came to removing the basin part of the mold I found that nothing would lift out. The unscrewed back had shifted forward slightly allowing concrete to form a slight bulge on the sides. Although the back piece could be pushed forward and wiggled out, the side pieces were too rigid and would not budge. So I had to use a pry bar and apply some force, a lot of force in fact and that caused the entire side to break away. This made getting the rest of the build-out much easier to do but rendered the sink useless. So I used the broken piece to experiment with. I applied the grinder to the surface to get an idea of how the polished surface could look. I used my "wet and dry" paper on the basin side to see if it would work and it did but if I can duplicate how the basin interior came out I won't have to. I will have to construct my basin build-out from a less rigid material such as styrene for the next attempt.

Before you see the pictures let me tell you what we like and don't like about the results. The drain depression worked perfectly for the drain I bought. I will describe what I did in a future post. The interior of the sink came out smooth and shiny. It is also marbled perfectly and requires just a few voids to be filled with a colored slurry. We really like the way it turned out and we like the color result. The counter top is another story. It is too chunky in the right corner with red color and looks unnatural. However, the ground surface with the black coloration looks great and very similar to our kitchen counter top. If the counter top and front was black and ground down a little and the basin marbled and smooth we would have the perfect combination. The entire sink sits 2 inches too high on the base. This is because the slope of the basin does not clear the wood frame of the base to sit the the air space that I have. For this reason alone I would have to make a new sink any way. So overall this was a good experiment. So, here are the pictures you have been dying to see!

The entire basin with drain resting in place minus the entire left side.

The left side with a ground surface to show aggregate in the concrete.

The gap at the base of the sink and the frame.

And finally this!

The start of a modified mold. I have raised the sides by the 2 inches that I need to eliminate that gap!
I will be sure to take pictures of the entire process as I make the spawn of the spawn of E.L.V.I.S.

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At 10/17/2007 9:04 AM, Blogger John said...

Pretty cool. Once the sink is polished/sanded, what comes next? I assume that you'll need to seal it with something, right?

At 10/17/2007 10:15 AM, Blogger Ragnar said...

Whoa, that's incredible!
Did you consider rounding the bottom edges of the interior mold? It appears polishing and especially cleaning of the finished sink would be easier that way.
I already mailed the entry to my cousin who wants an extra large custom kitchen/utility sink and was fascinated by the idea. I think the crucial issue for him would be to get the diamond polishing set at an acceptable price in Europe.

At 10/17/2007 8:03 PM, Anonymous Anonymous said...

I think what you are doing is amazing. Really amazing. I can't see myself ever making a concrete sink or countertop but for the money, I'd try it before buying anything made of granite. You have so much more control over what you get too.

At 10/27/2007 12:06 PM, Anonymous Anonymous said...

this is mind bogglingly fantastic. go you.

At 11/27/2007 3:00 AM, Blogger Admin said...

You should consider making a mold from fiberglass. I'm not sure if it will work with concrete or not, but i do know that it is considerably more versatile when you're talking about inverse angles and such.

That's what I'm hoping to do for my bathrooms here pretty soon. only I believe I'll actually have to make the whole concrete counter as well.

Great idea on the marbling effect.

At 9/28/2008 11:33 PM, Anonymous Anonymous said...

Its been a while now.... and I'm considering building a Laundry type sink for my studio.

How has your sink building progressed? Do you have an install shot?


At 9/29/2008 1:20 AM, Blogger Gary said...

Check the entries for November and December 2007 to see the finished sink.

At 2/05/2009 12:44 AM, Anonymous Anonymous said...

I'd like to know more about the sanding polishing process. How do you get into the concave corners?
What is wet dry sanding?

At 2/05/2009 1:17 AM, Blogger Gary said...

You can buy diamond impregnated polishing sponges for awkward surfaces. Wet/dry sanding is done with wet and dry sanding paper which is generally very fine grit and black in color. It can be used to sand dry surfaces or you can wet the paper to lubricate it. I believe it is also called silicon paper.

At 11/20/2010 12:43 AM, Anonymous stainless steel utility sink said...

I always wanted to make a concrete sink but I don't have any idea on how to build it. I want to thank you for sharing this little tutorial. This will help a lot.

At 10/04/2016 10:24 PM, Blogger Unknown said...

Where is part 2?

At 10/04/2016 11:28 PM, Blogger Gary said...

Look in November 2007 for several sink follow up posts. None are labelled Part 2 but there are several that show how I made the mold and the finished product.

At 2/26/2020 8:53 AM, Blogger Ash Green said...

Thank you so much for such an informative piece of information :)
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At 4/12/2020 7:48 PM, Blogger Nino Nurmadi , S.Kom said...

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