Cement Slab and Aggregates

[Kyngfish]

Hi All.

Trying my hand at making some terrazzo slabs, and I'm getting pretty close to a good mix. One issue I'm having to get it perfect though, is that since I'm using really different sized aggregates (from sand all the way up through chunks of stone) - the mixture gets hard to mix all together, so what I've been doing is spreading the bigger stone down at the bottom of the mold first then laying in the cement and sand and smaller aggregate mix. Once I shake everything out and everything settles though, even after polishing, the larger stones sort of settle into the middle of the cement as opposed to staying at the bottom. So basically, you don;t see them in the polished aggregate.

I was thinking of gluing them to the surface of the mold but I'm worried that super glue might create bubbles in the cement, and glue gun would be worse. I'll still probably try that for this next test attempt, but wondering if anyone here has better ideas.

 

[rustyjames]

Terrazzo is typically chips of aggrate broadcast over the wet concrete then ground and polished.

 

[Don1357]

It is supposed to get hard to mix. It is also important to mix it for longer than you think you should; once everything is mixed together you are about half way there.

Once mixed it is then easy to cast; dump on mold, tap, done. If the mold is deep enough you may need a lot of tapping to get the air out. Deeper than that, time to pull a tool.

 

[Kyngfish]

Terrazzo is typically chips of aggrate broadcast over the wet concrete then ground and polished.

Yeah. Fair point. Maybe I need to mold it backward. Right now the aggregate is going on the bottom and I’m pouring the mix over it then polishing it down to show the aggregate. The problem is that the larger pieces I want to highlight seem to float from the bottom upward to the top.

 

[Kaizen]

Yeah. Fair point. Maybe I need to mold it backward. Right now the aggregate is going on the bottom and I’m pouring the mix over it then polishing it down to show the aggregate. The problem is that the larger pieces I want to highlight seem to float from the bottom upward to the top.

So you are kind of making a countertop? Demold and flip and grind?
Are you vibrating the forms? That normally will help everything settle. But if these big pieces are light like lava or porous it might float.
I used a jitterbug sander from hf under the mold. No paper just keep doing it till you can’t and see how that works


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[mobetta]

maybe do it in 2 steps. get the big aggregates set at the bottom of the mold then add your fill material

 

[Mr.N]

Hi All.

Trying my hand at making some terrazzo slabs, and I'm getting pretty close to a good mix.

I was thinking of gluing them to the surface of the mold but I'm worried that super glue might create bubbles in the cement,

Keep going for a good mix.

What do you want as a final product?