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concrete molds

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shawn
Posted: Thu Jan 31, 2008 9:11 pm Reply with quote
Joined: 26 Mar 2006 Posts: 5
i've tried to switch from wood molds to concrete but ended up throwing money out the window! has anybody had success with concrete molds in conjunction with hydrolic presses. because i need some advice because all of my nmolds have cracked .!
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pennswood
Posted: Fri Feb 01, 2008 9:52 am Reply with quote
Joined: 14 Sep 2003 Posts: 213
concrete molds,
cheap, but it takes about 30 days for the concrete to cure,
if you jump the gun and use them to soon,
they will crack, almost explode under pressure.

we have used polyurethane casting media,
cures overnight, lasts forever.
but it costs around 400.00 per set.

now the bigger problem is why are your molds cracking?
wooden molds, what type of wood?
how did you get them properly offset?

the top and bottom molds should not be the same.
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cortex
Posted: Fri Feb 01, 2008 1:24 pm Reply with quote
Joined: 12 Aug 2006 Posts: 17 Location: Belgium
I use concrete molds too and the trick to prevent cracks is to put the molds in an iron case that holds them together and keeps the pressure inside the concrete. I do get minor cracks but I can do at least 500 decks per mold.

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boss
Posted: Fri Feb 01, 2008 8:36 pm Reply with quote
Joined: 19 Nov 2007 Posts: 227
this is one of my concrete molds, be sure to use plenty of rebar and wire screen.

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sk8bones
Posted: Sun Feb 10, 2008 6:04 pm Reply with quote
Joined: 28 Sep 2004 Posts: 540 Location: Oklahoma City
It has to be uneven pressure. Concrete does well under compression, but if the pressure is uneven it undergoes sheer stress and cracks. The iron case sounds good. You could also prestress the molds. Stretch cables inside the mold in a mesh pattern. Probably much easier to make a box though.
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looess kroose
Posted: Fri Mar 07, 2008 1:03 am Reply with quote
Joined: 05 Mar 2008 Posts: 1 Location: Toronto
could anyone PM me with photos or tips?

this is the only thing im a little sketchy on in my head (worked out alot of the logistics in my head, good to find this place and verify which will work best)
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