My First Concrete Sink

As many of you that read this blog know, I am doing a concrete sink project that will be in the shape of a guitar and used outdoors. It is a really big project with the counter top being 8 foot long. I have been taking my time with this sink because it will be my first sink. If I wanted to do it like my kitchen counter tops and make it with the hand pressed technique I could have already been done, but I want to try something new.

If I were to do the hand pressed look which makes it look more like granite or marbled, I would have to slurry coat the entire thing to fill in the voids, and also do this deep inside the sink. Then I would have to sand it several times to get a glossy finish. That’s OK, but I really do not want to slurry this one if I do not have too. Nor do I want to sand and sand and sand. I want a more machined look, crisp, smooth and clean.

This can be achieved two ways.  I can either wet cast or spray the concrete.

If I wet cast, that’s simply a wetter mix that is really flow-able and I can just pour it into the mold. This is good, but my counter top thickness is 1.5 inches and the sink is 6 inches deep. In order to wet cast I would have to build my mold up in tiers so that I could pour the counter top, cover it with more melamine, then build sides around the sink and pour some more. This will require more concrete mix and more melamine.

If I spray the concrete, it will be a GRFC mix (glass fiber reinforced concrete) and I will not have to use any metal bracing in the concrete like I would have to do in the other two types of concrete casting. Whats so cool about doing this, is that not only will it use less concrete, but I will not have to build up a two tier mold, will not have to add metal bracing, will give me a smooth finish with less if not no bug holes to fill.

I really really wanted to do GFRC but I have never done it before. When I researched it I kept finding out that I needed a really large air compressor. I needed a hopper gun specifically designed for spraying concrete, and I had neither of these things. I only have a 2.5 horsepower 15 gallon compressor.

I read in very few places where some guys were getting by with even smaller compressors. This made me think it might be possible after all. Next I needed a gun to shoot the concrete with. Luckily a friend of mine has a drywall hopper gun. With a few modifications to tilt the hopper bucket further back using a 45 degree PVC fitting, I think this too will work.

Drywall Hopper Gun used to Spray GFRC

After I got the hopper gun I plugged it into the compressor to see how it works. Now I know why they say I need a large compressor. When you plug the gun in, its constantly blowing air. All the trigger does is dump whats in the hopper in front of the moving air.

I came to an realization that in order for this to work I was going to need to regulate the air and be able to turn it off and on when I needed it, so I could save the air and this way my compressor would run out of air so fast and I have to wait on it to fill up. A quick trip to Lowes to find what I needed and all was well.

Now to test.

OK, so I need to test this stuff out, but on what? Not going to waste an effort, so I remembered this small plastic pond thing that I picked up at Lowes several months back that wanted to one day make a sink from.

Pond Liner used for Concrete Sink

Well today was that day. I quickly fashioned a standard mold, its quite small actually at 19×24 inches. I affixed the pond thingy with silicon, added my tail piece for the sink drain made from a PVC pipe and rubber gasket, then 3 other pieces of PVC for the faucet, a typical 4 inch bathroom faucet. Now I am ready to spray, or try to.

Concrete Sink Mold

I made my mix and poured it into my hopper. I then sprayed a little on a piece of cardboard to see how it would spray.

I felt confident I had most of it all right, and I began to spray my mold. After it set a while I back-filled with my not so wet mix. I did this by hand. Everything looked good and I covered it for 2 days. On the 3rd day I took it out of the mold and I was delighted at what I was seeing. For my first run at this it was pretty flawless. There were a few bug holes to fill inside the sink and seal it up.

First sprayed layer of GFRC

Concrete Sink

This was a great first test run and I think I will do one more of this same sink and make the counter for it larger, before I tackle my outdoor integral guitar sink.

Stay tuned.