Casting a thin concrete slab

[MB77]

Considering casting a slab for the TV bench, which is 1800x400mm. I'd like it to be about 15-20mm thick, how should it be reinforced and with what to make it work?
Should I use regular fine concrete, or is there something special?

(Is this thread in the right forum?)

 

[Enk Projektet]

I would probably use some 12mm iron along the length and then mesh on everything.... fine concrete or expanding concrete is what I would have tried....

 

[mexitegel]

Check out fiberbetong, I have a feeling that it doesn't require as much vibration to achieve a smooth surface,

 

[pelle242]

I think it is too thin, people usually make countertops at least 40mm. Expanderbetong is said to have fewer air bubbles and shrink less.

 

[MB77]

I think it's too thin, 40mm is what people usually make countertops at a minimum. Expanding concrete is said to result in fewer air bubbles and less shrinkage.

Yes, it's certainly thin, but there must be a solution to this. I've surfed around a bit, and there are table tops that are around 20mm. Making it 40mm would look very odd.

 

[Enk Projektet]

Yes, it's thin, but there must be a solution to this. I've surfed around a bit and there are table tops that are around 20mm. Making it 40mm would look very odd.

I absolutely think it will work... just be a bit careful when carrying it... it's not a lot of money so it's worth a try...

 

[jhenrikj]

Concrete slabs that are so thin are not reinforced but cast with metal fibers mixed into the concrete.

 

[MB77]

I definitely think it works...just be careful when you have to carry it.....it's not a lot of money so it's just a matter of trying it.....

Yeah, you'll probably have to carry it with support. I'll rummage around in the garage and see if I can throw together a mold.

 

[Enk Projektet]

Don't forget the camera....

 

[Nilsson2]

I would avoid rebar when it is so thin as you risk ghosting. Use polyvinyl alcohol fiber or fiberglass. We cast a slab approximately 1600x350x19 where we used pva-fiber. The bigger problem was preventing the slab from bending during the curing process.

 

[MB77]

I would avoid rebar when it is so thin as you risk ghosting. Use polyvinyl alcohol fiber or fiberglass instead. We cast a slab about 1600x350x19 where we used pva-fiber. The bigger problem was preventing the slab from bending during the curing process.

Do you mix this directly into the concrete then? Or does it lie in layers?

 

[Helioz]

It is involved in the concrete but you don't need to mess with it yourself. Use Finja Repair Concrete instead, it contains fiber and is available in standard 25-kilogram bags at most hardware stores.

 

[Ogguls26]

Hi Nilsson2,
exactly the problem I get when casting thin, trying to make kitchen countertops in 25 mm, casting with 1 part concrete 2 parts sand, angle iron + chicken wire and thin reinforcement mesh. The slabs warp/bend during curing. How did you prevent it??? Very grateful for an answer as I'm pulling my hair out with this right now)

 

[AXS]

I have cast desks of 1 square meter, 22mm thick, without problems.

Quite fine-meshed reinforcement mesh, expanding concrete, and a stable form. After curing, I glued a 4mm plywood underneath the entire thing for extra reinforcement, which also made it easier to attach legs and similar.

Got a crack in one of the slabs, it was easy to make it invisible with some self-leveling compound and a sponge.

 

[Ogguls26]

I have cast desks at 1sqm each, 22mm thick, without issues.

Quite fine-mesh reinforcement net, expansion concrete, and stable mold. After curing, I glued a 4mm plywood underneath the entire thing for extra reinforcement, which also made it easier to attach legs and the like.

Got a crack in one of the slabs, was easy to make invisible with a bit of levelling compound and a sponge.

Good afternoon,
I think I will try with a pre-mixed concrete in a bag, I am casting in sturdy molds anchored to a table but still the slab bends about 1-2 mm so it becomes like an elongated U.
To me, it seems like there is shrinkage on the upper side of the casting when it sets even though I water it!
If anyone knows why it would be interesting to get an answer