Sand & Cement

Discussion in 'Sand Casting' started by Skratch, Jan 22, 2022.

  1. Skratch

    Skratch Silver

    Has anyone tried mixing sand and portland cement in a damp mix to try to make a reusable tamped
    mold? I know the mold would have to cure, probably a few days. We used a light cement to sand mixture to form the draw off slope in bin bottoms in grain elevators,
    then top coated with a layer of strong mix cement. The light mix would set very stable.
    Just an idea, I'm new at this and just a hobby to keep me busy.

    Thanks, John ,,,,,
     
  2. Cement as far as I know has water bound up in it after curing, you can get steam explosions and flying concrete from the hotter metals spilt on even old concrete floors.

    Then you have cracking as the hot expanded metal cools and contracts if the inner core material can't crush as the contaction occurs: in green sand it's not truly a solid and for resin sand the glue lets go from the heat.
     
    Last edited: Jan 22, 2022
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  3. Tobho Mott

    Tobho Mott Gold Banner Member

    Sandrammer on youtube did a couple videos where he tested a recipe he found in an old foundry text for cement bonded molding sand.

    Seemed to work well for ingot molds. But shapes that would require the sand to have some give to it during solidification shrinkage might end up tearing themselves apart.

    I've been reusing a petrobond ingot mold for a while now, but I'm sure that takes a toll on my good sand. So I've been thinking about maybe trying this too when I have more time to experiment.





    Good luck!

    Jeff
     
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  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hard to see why anything other than hot rolled steel is needed for aluminum but for other, seems like fire clay might stand a good chance for an ingot mold, if you keep it dry and preheat it.

    Best,
    Kelly
     
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  5. Skratch

    Skratch Silver

    Thanks guys, as I understand it using a pattern with an inner core wouldn't work because of the outer metal contracting around the
    inner core wouldn't let the inner core move or crush. I hope I got that right. I'll just be pouring items like bronze age daggers and axes.
    I thought of the ancients using stone molds and wondered if the cement mix would work much the same. I see that the curing might be
    an issue, we have very low humidity here in New Mexico, sometimes down to single digit so atmosphere absorbability shouldn't be much
    problem. Drying the mold slowly in an oven at low heat might remove most if not all moisture as the mold halves would only be 2" thick.
    Just an idea from my idle mind .;)
    On another note, I've sifted some sand/adobe clay down to .020 - .030. I haven't tried it yet for compacting yet but will post results if anyone's
    interested.

    Thanks again,, John,,
     
  6. Tobho Mott

    Tobho Mott Gold Banner Member

    I don't think Sandrammer's recipe is any more likely to steam-explode than a greensand mold (which also as water in it). It's a sand mold that uses some cement as a binder, not a cement mold with some sand in it, if that makes sense.

    From what he said in the video, I think the cement sand is probably too hard to make the core for an axe with a hollow eye for the handle, but you could use a more collapsible material for the core. I've made some bronze axes and spear points, but only in greensand or petrobond. But hey, they used stone molds in the bronze age so maybe this could work too...

    Not having to weld or preheat steel ingot molds, or ram up a new ingot mold in molding sand very often, that's the main reason I've thought about trying the cement sand mixture. I do have about 1/3 of a bag of fireclay left over from my old Gingery charcoal furnace build though, so I'll consider that... :D

    Jeff
     
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  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Still need to high fire it fist

    Best,
    Kelly
     
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  8. Tobho Mott

    Tobho Mott Gold Banner Member

    Another point for the cement sand mix... :D

    Jeff
     
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  9. Ironsides

    Ironsides Silver

    Cement sand works really well as a core sand. Never had any problems with cracking of my iron, bronze and aluminium castings. Also there is no need to dry out the cores before placing them into the mold. There is a big difference between core sand made from cement and concrete used for buildings and road ways and that is the amount of water and cement used. The only reason why I stopped using cement sand cores is epoxy breaks down to a powder. Have a look at my video making cores for cast iron.
     
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  10. Skratch

    Skratch Silver

    Finally got a try at the adobe clay/ sand mix, just took a screen and sifted about 40 lbs, it worked great, no other
    added ingredients needed. Making an Otzi axe, good pour.

    John,,,,
     
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  11. Skratch

    Skratch Silver

    Another experiment,, change the mixture by adding clean sand from a dry wash, dirt and clay washed out. Didn't keep
    a record of what to what, should have,, next time maybe. Anyway it rammed well, made good cast, little rough finish
    even with my fine sifted sand, gotta work on that,, any suggestions ? I used the previous castings that had voids as patterns by
    using spackling compound to fill then sanded smooth. Seemed to work fine. Pics are before and after. Next try going to use a bit of portland cement in the mix, just for the heck of it.
    On another note, still having problems with the burners whistling and huffing, wondering if altitude might have something to do
    with it, 5000 ft. orafice size is .045.
    Thanks for any thoughts,,,,
    John,,,

    IMG_20220208_215909.jpg
     

    Attached Files:

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  12. Post some pics of your furnace over on the "Furnaces and their Construction" topic, how big is your lid hole?: it might be choking your furnace.
     
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