Hiding aggregate in concrete pour

[S Rated]

I'm unable to find any information pertaining to "floating" concrete when it is poured into a form. My ultimate goal is to hide all coarse aggregate from all surfaces when poured into a mold. I plan to use melamine surface for the mold.

So far, I've come up with two alternatives: Only use sand as aggregate and option two is to pour standard concrete mix and then after braking mold, cover all surfaces with mortar mix. While I plan to have a rebar skeleton, I'm unsure of sand-only concrete strength. And option two is not ideal as I'd like to bypass additional steps post mold braking, if possible.

What I'm making are table legs that will be about 6"x3"x40". Surface finish I'm looking for is similar to this --

TIA, Dennis

[Nehmo Sergheyev]

I would hesitate to make anything concrete only 3 inches thick. Is concrete the best material for this job? Why do you want to use concrete? If you just want some rectangular prism shaped parts that are heavy, consider using some scrap granite.

~~( Nehmo )~~

[Rick Samuel]

Fiberglass, loose fibers. No idea how much, tho

[S Rated]

Unfortunately, yes. I'm going for concrete look.

[RicodJour]

Oiling or waxing the form before placing the concrete, vibrating the form after the concrete is placed and using a super-plasticizer will give you a nice smooth finish. There is no reason to skip the coarse aggregate. You could use pea gravel instead of larger stone if you're really concerned, but it's not that big of a factor. You can get an imperfect finish with any concrete if you don't take care of the details and conditions.

What SN was talking about with his concern about the thickness of the concrete is having enough concrete covering the rebar. Ground contact concrete requires 3" coverage by code (that's for construction), but your situation is different. The best thing to use would be epoxy coated rebar.

Melamine is probably not a good choice. Melamine is on particle board and does not like water - it swells and would ruin your form in short order. Use MDO plywood and use diesel/kerosene to lubricate the form. You can use a palm sander to vibrate the form from the outside.

R

[Cwatters]

I've expermented with left over concrete dumped onto 4mm plastic sheet. Got a dark grey near gloss finish. Were a few bubbles but then I didn't make any effort to prevent them.

[Roger Shoaf]

~~( Nehmo )~~

I guess you have never seen an old fashion laundry sink. These were only about an inch thick.

Also consider how thick a regular old cinder bleak is.

They also make roof tiles and Hardy plank from concrete less than an inch thick so I think the design of the item to be cast and the formula of the concrete will make a big difference to the final useable thickness.