On Sep 29, 1:57*pm, "charlie"
wrote:
"fourrings" wrote in message

...



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 --
http://www.cgmprecast.com/images/picnic_table_leg.jpg.

TIA,
Dennis

i formed some concrete countertops using melamine as a form just using a
high strength sack mix. i formed them upside down so that the surface
against the bottom melamine was the top surface after flipping. i didn't
have any aggregate showing in either the sides or tops. i think the trick
was to vibrate the concrete when the mold was half filled, and then again
after it was full.

Dennis-

Charlie is correct. I have formed concrete in plywood & waxed
cardboard (SonoTube).

The resultant finish (smoothness) on the concrete is determined by
the smoothness of form & the amount of vibration.

The waxed tubes often resulted in a concrete surface as smooth as
glass,
plywood forms yielded a much rougher surface.

The cement paste "cream" adheres to the plywood & pulls off the
concrete mass yielding the rougher (almost a wood grain finish)

Since you're using melamine as a form surface, you've got a really
smooth surface.

On the form open face, vibration will cause the aggregate to settle
below the surface so hand tamping will most likely not be needed.


On our formed laboratory models, we used a 3/8" gravel mix that was
70% sand, 30% gravel. This mix typically yielded 28 day compressive
strengths in the 4000 to 5000 psi.

cheers
Bob