Polished Concrete Garden Kitchen

Hello fellow builders,

Given the fact that I'm now enjoying my summer vacation, I thought it’s a good moment to write an instructable. So I decided to build the outside kitchen with the concrete top I had planned a while back. Just a basic design with a flat top and two sliding doors. The top will mainly be used to place my little wood smoker on, to make for example delicious smoked salmon. I opted for the concrete for the top because the smoker gets rather hot which shouldn’t be a problem for the concrete, and since the thing comes outside it has to be weatherproof.

The cabinets will be built in compactboard, a very hard and durable material made of wood fiber and resin. Used mainly in paneling for buildings or as tabletops for office furniture. The board I used had a former life as a top for a desk, and still had some coffee stains, but other than that, it’s a real nice material to work with, and completely weather proof.

The top will be made with inlaid glass and different colors of concrete and, I hope beautifully polished.

This project is almost totally build with things I had lying around, so the cost are minimal. The compactboard came second hand from a workshop, and the only the concrete from the store. The rest of the things I used were all leftovers from other projects, so I spent about 20 Euro's in total, not counting the tools. But If all the material had to be bought new this would easily climb up to 300 to 400 euro, since the compact board is rather expensive ( about 170 Euro per plate )

60 kg of concrete pre mixed, extra strong.

Two plates of compact board

melamine laminated chipboard

Cement dye red

joint mortar white

joint mortar black

joint mortar beige

Some screws

Tools:

Table saw
cordless drill

Power drill

Power hammer drill

Axel grinder

Router

handsaw

polish disk set

wiretap M3 and M4

I like to draw out a complete plan for the things I make, for two reasons, It’s more easy to find flaws in the design, but more important, when the actual building starts it speeds up the building process quite a lot. Which makes it much just more fun.

I’m in the happy situation I have access to Microstation through my work, so I used it to draw out the plans for this build

concrete mold is made in the laminated chipboard. A cheap material with a very smooth finish, which will make for a nice flat surface. Al the corners are filled with silicone sealant. Not to seal them but just to make them round, for easier sanding. The hole formwork is spayed in with silicone spray, to make sure the concrete doesn’t stick to it. I used silicone, because I had it, but this can just as well be done with any vegetable oil.

In the bottom of the concrete top I placed a plywood ceiling plate, to make the concrete top less heavy, and make it easier to attach the doors to the top. The plywood ceiling plate has a lot of screw sticking out, which will ensure that it is tightly fixed to the concrete.

Since there are two conduits with antenna cables on the wall were the kitchen is coming, I had to make some openings in the top. For this I put two rolls of cardboard in the mold to have an opening in the countertop. And I screwed a double strip of plywood, wrapped in plastic foil, to the front side of the plywood ceiling plate, to make a cavity in the top for the doors

The wire frame is made from 3mm galvanized steel wire. For the outsides I folded the wire double and turned it together with an electric drill, double to make it stronger and turned to make it strait. The wire in the middle is also turned with the drill. When you do this while pulling lightly on the drill the wire becomes totally strait.

For an extra sparkle I put in some glass beads. Made from the lit of an old frying pan. Had to be reduced in size, so I just smashed it with the hammer

Since I wanted colorful concrete I first splashed in some white joint mortar followed by some black and then some beige joint mortar. Then I made the first bit, about 2 kg, of concrete, and mixed this with the red cement dye.

This dye is in my family for a very long time since it is a leftover from a project my father made over 30 years ago, so finally a good use, although I only used a bit of it.

I put some of the red concrete in the mold, and poured in the rest of the 20 kg bag in the mixing bucket wich made it grey with a hint of red. I then carefully filled up the entire bottom with grey concrete, making sure the other colors and the glass beads didn’t move to much, made more concrete, and filled the mold up till there was a thick layer on the hole bottom, and the mold was about ¾ full.

Now it was time to put in the steel reinforcement, I placed the frame on the wet concrete and pushed it in a little. Poured in some more concrete till the mold was so full that pushing the plywood in would let the concrete flow to the side and up, to make sure the plywood and the concrete together filled op the mold. I made the concrete rather wet and fluid, so it could flow when I pushed the plate in.

After the plywood was placed I pushed it down and to the right location, and secured it with a few pieces of scrap wood and some screws, after which the rest of the mold could be filled up with concrete.

To get the air bubbles out the concrete I made the mold vibrate with a power finishing sander. Next time I will do this earlier and longer because I still had to much bubbles.

While the concrete was curing I started the work on the cabinet. I cut out all the pieces on the table saw. I used a blade which had special sharpening for this types of material ( it can also saw Aluminum ) and this makes such nice cuts I don’t even have to sand down the edges. Although I did cut the corners of the horizontal plates with a 45dgr router bit.

The rails for the doors were also made on the table saw from strips of the compactboard. I just took these many times over the saw, every time adjusting the guidance and/or angle, to take away all the excess material.

I bolted a piece of wood 40x40mm to the wall to support the top, and strips of compact board to support the bottom and the shelf. The cabinet is screwed together just as you would with one of wood, only because the compact board is so hard, you have to pre drill everything. I used screws 4x40 mm for this and drilled holes of 3,5 mm. so the screw only has 0,5 mm to get grip. But that’s more than enough. If you turn them to hard they don't come lose, they just break.

The weels on the doors where bolted on with M3 bolts, just tapped strait in the board with a standard machine tap. For the door on the outside I raised the wheel by a 17mm block which I screwd on the door with two M4 screws.

After 3 days of waiting I couldn't stand it anymore and decided it was time to see how the top turned out. First I pulled out the strips in the bottom side for the door cavity, Turned the top around and removed all the screws. After which the melamine plates where carefully removed one by one.

I was really pleased with the result. I even almost decided to leave it like that, but still, I decided to start grinding the beautiful smooth finish to expose the glass and aggregate in the concrete.

It was day 4 after the pour and I started with grinding with the 50 disk, dry in the axel grinder, and there was dust, a lot. Dry grinding goes much faster than wet but also gives a rougher finish, and beautiful clouds of dust, but for the beginning the finish isn’t important, although the clouds are somewhat annoying.

When the glass and aggregate of the concrete where coming through the surface I was glad I decided to polish. And after about an hour of grinding the hole top layer of one to 2 mm was removed, and the support disk had lost about half a cm in diameter because of the grinding in the corners .

I flushed the hole top with the garden hose to have a look how it will turn out. At this time you can really see what the end result is going to be, and it will be looking better every minute from now on. I switched to the 100 disk and started the wet grinding. No more dust. After about 15 minutes with the 100 disk, which was vibrating so hard that to screws from the safety cover of the axel grinder fell out and had to be removed, the support disk decided it was time to die, so it left the axel grinder and went sailing. How happy I was that I’d decided to buy the extra set. I switched to the electric drill with a piece of an M10 bolt and finished the 100 grind.

Because there were some small holes in the surface, I made a bit of concrete of which I had sifted the stones out, and filled all the holes. Waited a day for this to dry and gave it a quick sand over with the 100 disk wet. Then the whole surface was polished with the 500 disk.

While polishing with the 500 I noticed here and there pieced of glass popping out and the white joint mortar was really a bit too soft to polish. Seems like I began to soon with the sanding. So I decided to fixate the top with Floor sealer, and this turned out very well. This sealer is suited for concrete and outside application, and gave the top a nice smooth finish.

If the sealer ever wears out I will just restart the polishing.

The top is laid on top of the cabined and secured with some glue. Then the top rail for the doors was screwed in the cavity of the top, and the doors where placed in the rail. Fitting was tight, so the top door had to be on the rail while it was screwed in. The bottom guidance clips where simply glued to the doors with polymer kit and the kitchen was finished. Well almost. I did plan to carve a nice picture I found on a T-shirt in the doors with my brothers CNC machine, but unfortunately there is a problem with the machine, so this will have to wait till the machine is fixed.

But I will post the pictures when the doors are finished.

Although I’m very happy with the result, next time I would do a few things different. I would definitely rent a professional sander because this would cut the grinding time in half, and give a better result. And wait at least 10 days before starting the grinding, so next time the result will even be better.