what is the minimum thickness of concrete that i can pour?
i want to make a lattice with .75"x.75"x.75"
what kind of concrete would i need?
>>971302
Depends on the performance you need. Concrete is very weak in tension, especially if the aggregate is almost as large as the thickness. Cement and sand without large aggregate should hold together in a .75" cross section, especially if you mix in reinforcing fibers.
However, that may not be the best material to use. Plaster is more suited to detailed casts. Fired ceramic is stronger. Epoxy resin is tougher. What do you need it for?
>>971310
>Cement and sand without large aggregate should hold together in a .75" cross section, especially if you mix in reinforcing fibers.
so a mix that is as fine as possible (concrete and sand) would work best, here?
and what serves as reinforcing fiber?
>What do you need it for?
it's just a personal project. it's related to an architecture project that i'm working on. and i'd like to have it as a neat study conceptual model.
ideally, it's concrete. the materiality is kind of important.
>>971311
and here is my proposed construction method.
i make the negative out of foam modules, and then slide them into a 2" wood cube box. i pour the concrete (here, i'm not sure if the concrete will fill all the cracks)
at the end, i use acetone and a pick to dissolve the foam (eps).
thoughts?
>>971313
Sounds like something id like to try.
>>971313
Try it. Only thing you'll waste is the time taken to carve the foam out. Maybe make a test run with a single pane of lattice first.
>>971311
>>971313
>so a mix that is as fine as possible (concrete and sand) would work best, here?
Concrete is a mix of portland cement (a fine powder), water, sand, and larger aggregate. The cement and water react to form hydrate crystals that hold the rest together. So straight cement, fine sand, and water. Alternately, use a grout mix, which may have better flow properties.
The reinforcing fiber is usually tailored to the application. It sounds like yours is light-duty and short-term, so most any fine, chopped fiber should help. Short lengths of medium steel wool or fiberglass would probably work well. Shorter for better flow, longer for more strength. Maybe try a few different mixes with small test pieces.
>i'm not sure if the concrete will fill all the cracks
In real-world concrete pours, this is addressed with vibrating probes that shake the concrete and dislodge bubbles. Maybe run a .25" steel rod into the vertical shafts and pack in each layer as you fill it.
Sounds plausible, if messy. Be sure to spray or line the wood with something that will release the concrete easily. Be sure to use solid EPS foam rather than the expanded bead kind. The voids will cause problems. Rounding the edges slightly will reduce stress concentrations in the corners, which may be worth the effort.
>>971328
awesome advice. much appreciated. thanks!
i'll post results, as i may try something this weekend!
I would use a quickset cement like Quikcrete. It will not have any aggregate in it. Reinforcing fiber is a good idea for strength but it may affect your surface finish. I was very surprised at how well concrete picks up surface detail from the mold (I played around with bottles and cardboard boxes).
>>971302
non shrink grout.
>>971328
>In real-world concrete pours, this is addressed with vibrating probes that shake the concrete and dislodge bubbles.
I've done something like this before; just mix the concrete pretty thin and use an orbital sander on the outside of the box. Works really well.
>>971517
Ah shit beat me to it
>>971302
Some kind of counter-top mix should work.
>>971313
You could always make a negative out of wooden bars and cubes and hold them all in place with long threaded rod capped with a nut keeping them under pressure that way you could remove the rod and pull out the wood one by one to reuse them.
It really comes down to steps you want to take and time
>>971313
wy dont you make a positive aut of foam and than laminate it with fiberglass
>>971302
why not reinforce the concrete with steel rebar or just go get some threaded rods or something from homo depot
>>971689
Concrete expands slightly when it cures. It would clamp down on the blocks and you'd never get it out again.
It might work if you used HDPE blocks and epoxy granite (though you'd probably still need a press to get them out), but OP specifically wants concrete.
>>972144
It sounds like it's going to be handled and moved around, so it's going to have to withstand impacts. The grid lattice design concentrates stress at the corners, which are very small for a concrete structure. And concrete often cracks naturally as it sets. I think that some reinforcement to keep it from falling apart at the first crack is probably a good idea.
