Casting a concrete countertop - pictures, questions..

[Dublin]

Does anyone know how thin a slab you can cast? I want to have a shelf for a coffee maker & kettle and thought it might be cool to have one in concrete. But is it possible to make it 20mm or would that be too fragile? The slab will be about 500x250mm

 

[callering]

Hello, we have cast many concrete slabs, ranging from fully flat colored ones to those resembling millstones in front of fireplaces. You can use regular pigment color for tinting. You don't need to color the whole thing; you can first lay colored concrete at the bottom of the mold and around the edges. Then insert the reinforcement. Then pour the rest. You vibrate it with a drill attached to the mold. In it, you place a piece of bent metal, e.g., a rebar piece or wire. It shakes well, and air bubbles immediately rise from the mixture. Secure the machine properly; otherwise, it will take off like a headless chicken! Never make the concrete too wet. We usually apply epoxy on the surface to achieve a good result for a kitchen or bathroom. It can become mirror-like if desired. If you let it drizzle a little on the wet epoxy, the surface becomes interesting. The small indentations can have irregular color variations from gray-white, making the black slab come alive. Regarding the reinforcement, you can use 6 or 8 mm rebar that you simply push down into the mix, or alternatively, use a reinforcement mesh. If working with thinner slabs, you can use a couple of layers of directional mesh. If you want to make a rough but smoothly structured stone slab, take coarse concrete and first cast a raw slab. When it has cured for about 15-20 hours, brush on cement and water a few times. First, you pick out the large stones that protrude. The surface becomes like from the Permian or Jurassic period with a limestone character. A pair of old jeans will polish the surface to a velvet-like smoothness. No one will be able to tell your slab apart from a natural one from ancient times! Sometimes we mix in a bit of stove clay (powder) and get a beige-gray color. Then you can brush around a little with cement and water to give it a speckled look. Finally, after a couple of hours, you can drum around a little with your fingertips to get a slightly bumpy surface. COVER WITH PLASTIC FOR A COUPLE OF DAYS to prevent cracking. Good luck with experimenting. Imagination should have no limits.

Calle Ring, architect and artist

 

[callering]

Hello,
You can actually cast a slab down to 6 mm. It's about the reinforcement embedded in it. A dense metal reinforcement in the form of a fine mesh is suitable for thin slabs. To handle loads, in the construction industry, it's about placing top or bottom reinforcement. The reinforcement is placed closer to the side that becomes convex under load.
Regards, Calle Ring

 

[JohanOLinda]

Cracked the mold for an 8mm yesterday. Turned out well, and held up during a short transport. 1800x650, 6 iron.

What is it that everyone wants to achieve through grinding? To remove the concrete skin and reveal the stone. The surface you get through regular formply is smooth, very smooth.

 

[Watchmen]

the first 1-3mm are weaker. So you get a stronger surface by grinding

 

[jeppeknaster]

From finally home.

http://www.tv4.se/1.283438?videoId=1.547458&renderingdepartment=2.18526

http://www.tv4.se/1.283438?videoId=1.547472&renderingdepartment=2.18526

 

[peppe400]

Hello

I have made a small concrete slab that is 70*70*5 cm, which I will use for a coffee table. I have sanded it by hand and finished with 1200 paper. The result is a fairly glossy surface that is slightly mottled. Now I need to treat it with something, and I'm wondering if those of you who have used paraffin oil can answer the following:

1. Does the mottling in the slab even out (like when you oil wood)?
2. When you apply the paraffin oil, does the concrete become significantly darker, and does the slab retain this darkness?
3. Does anyone recommend something other than paraffin oil?

 

[LiMa]

The flame-like patterns do not diminish; on the contrary, I would say, but that's kind of the point, as it is a living material. The dark color disappears when the oil dries. Several have recommended glass concrete, and epoxy also sounds interesting. It probably depends on what kind of surface you want.

 

[callering]

Hello,
my tip is to try different techniques. Take 5-6 ice cream containers and fill them with different mixtures. You can add epoxy or epoxy-mixed cement solution (Cement + water + 1/3 epoxy). When working with epoxy, make sure you absolutely don't get it on your hands - it seeps in and causes trouble.
You can apply pigmented coarse or fine concrete.
A fun technique is coarse concrete that you brush off the surface of after 10-20 hours. Then you brush on cement and water or epoxy cement. Then polish with cotton - your old jeans.
If you have a concrete slab you’ve cast, you can apply epoxy and then shower with water. You'll get an exciting surface.
Remember that nature has experimented with itself for billions of years. So you too might come up with some fun new variations. The journey into the unknown is filled with light.
You can mix in glass powder or crushed glass, marble powder from the paint store.
I repaired a broken brown marble staircase with a mixture of oatmeal and epoxy - no one saw the difference.
So get to work and let your senses soar - concrete is cheap.
Best regards, Calle Ring

 

[peppe400]

Thanks for the tips

In the end, I ended up with a product called stentvål. It hardly changed the appearance of the slab, just a few shades darker. The downside of the product is that it doesn't protect well against acidic substances, but that doesn't bother me much since the slab is for a coffee table.

 

[yps]

Can't those of you who have made some nice countertops post some pictures of different surfaces? I'm interested in a concrete countertop for the kitchen island, or alternatively buying one in composite stone, but they are so darn expensive.

Magnus

 

[mirage]

Can't you who have made some nice slabs post some pictures of different surfaces? I'm interested in a concrete slab for the kitchen island, or alternatively buy one in composite stone, but they are so damn expensive.

/Magnus

I'm working on a concrete slab for the kitchen. You can follow me at www.byggerhemma.se

 

[yps]

Cool, will read more later.
I talked to a floor sander myself last week, and he could come out and sand/polish a concrete slab if I cast it. Then the surface becomes very glossy, like HTC Superfloor.
Might be a tip.

/Magnus

 

[Overlander]

Is there no one else who has pictures of their concrete countertops??

 

[jeppeknaster]

are there DIY tips on finja.se