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My First Bag of Cement

Home Forums Research Engineering My First Bag of Cement

This topic contains 15 replies, has 4 voices, and was last updated by Avatar of elspru elspru 3 years, 6 months ago.

Viewing 15 posts - 1 through 15 (of 16 total)
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  • #1391
    Avatar of elspru
    elspru
    Participant

    got a 40kg bag of portland cement from homedepot yesterday.

    carried it in my hiking backpack to another store and to the bus.

    So now I’ve got it at home, any tips on where or how to keep it?

    Also any ideas for some initial projects or mixes,

    some way of testing it our perhaps.

    I have sources of sand from nearby freshwater beach,

    and can make ash by getting excess from using a wood-fired furnace,

    I’m thinking maybe my first large project will be to make a double-chambered pottery/cement furnace.

    though meanwhile perhaps there is some experiments or procedures you’d like to recommend in handling cement?

    for instance it says corrosive on it, so should I wear gloves, mask, goggles in a well ventilated area?

    or is it safe to just use a spoon or shovel and make it in a mixing bowl?

    #11982
    Avatar of Alan
    Alan
    Participant

    First, what exactly did you get? Ready-mix only needs water, and there are several types of ready-mix.

    For small jobs, most people mix it in a wheelbarrow or a used (free) 5 gallon bucket. You’ll need a shovel.

    Easy first experiment: By chance do you need to set a post somewhere, permanently?

    Corrosive: Yes, it is corrosive. Professionals often wear gloves, because they have to deal with it all the time. However, it isn’t really necessary for short-term exposure – it’s corrosive but not all that corrosive. It’s much more dangerous if you have to cut it or drill it later, and the dust gets into the air (and youg lungs).

    Hope that helps.

    #11986
    Avatar of elspru
    elspru
    Participant

    Alan wrote:

    First, what exactly did you get? Ready-mix only needs water, and there are several types of ready-mix.

    my purpose being to learn as much as I can.

    I got pure portland cement, it’s also good value.

    have source of freshwater sand and gravel from nearby stream.

    so at a 2/5 cement ratio I could techinically make a 100kg of boat.

    For small jobs, most people mix it in a wheelbarrow or a used (free) 5 gallon bucket. You’ll need a shovel.

    Easy first experiment: By chance do you need to set a post somewhere, permanently?

    for my first experiment I decided to make a cement tablet, used a teaspoon,

    took me a while to get it to a ratio where the letters would hold.

    Corrosive: Yes, it is corrosive. Professionals often wear gloves, because they have to deal with it all the time. However, it isn’t really necessary for short-term exposure – it’s corrosive but not all that corrosive. It’s much more dangerous if you have to cut it or drill it later, and the dust gets into the air (and youg lungs).

    Hope that helps.

    I’ll keep that in mind. I have some nylon gardening gloves I can probably use for forming it like clay.

    now in terms of curing it, which seems like the hardest part,

    should I leave it in my humid terrarrium, or floating on my aquarium?

    I figure floating on aquarium might simulate having a floating drydock.

    cement tablet floating on aquarium, surrounded by duckweed.

    calm aware desire choice love express intuit move

    #11997
    Avatar of J.L.-Frusha
    J.L.-Frusha
    Participant

    It will be a PITA to get the cured cement off of that plate… Next time, I would suggest way-paper and a flat table, or coated butchers paper…

    Later,

    J.L.F.

    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.

    #12001
    Avatar of Alan
    Alan
    Participant

    Generally cement has to be dry to cure. That shouldn’t be a problem with a dry dock, as a dry dock is – you know – dry. When cement dries it expels most of the water in the mix, so the more surface area where the water can be expelled the quicker it dries.

    I guess you’re talking about floating the plate in your aquarium – I suppose you could do that, but I don’t see much point in it.

    There is also a type of cement called hydraulic cement that can set in standing water, but it costs more. This was what was used when the Chicago River had a leak, almost twenty years ago. It is useful for repairs, but it is more cost effective to use regular concrete in a dry place for initial construction.

    #12002
    Avatar of elspru
    elspru
    Participant

    J.L. wrote:

    It will be a PITA to get the cured cement off of that plate…

    it was actually on a piece of plastic.

    it was easy to get off, but there were a bunch of bubbles on the bottom,

    perhaps it’s from lack of air-exchange.

    Next time, I would suggest way-paper and a flat table, or coated butchers paper…

    how about wax-paper?

    I wanna make a bowl shaped version, that I hope will float.

    calm aware desire choice love express intuit move

    #12003
    Avatar of J.L.-Frusha
    J.L.-Frusha
    Participant

    Yes, I meant wax paper. One way to do the bowl, would be to shpe if over a shaped mound of wet sand… As for floating, I hear the original cement pirogue is considered water-worthy, in whatever museum it is in… Matter of forming it to displace more water than its’ dry weight, after curing… Basically, don’t make the ‘hull’ too thick, in relation to the desired displacement… It’s possible that the bubbles were trapped, or off-gassed, as cement has an exothermic reaction, as is cures, even if it is a mild one…

    Later,

    J.L.F.

    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.

    #12006
    Avatar of elspru
    elspru
    Participant

    Alan wrote:

    Generally cement has to be dry to cure. That shouldn’t be a problem with a dry dock, as a dry dock is – you know – dry. When cement dries it expels most of the water in the mix, so the more surface area where the water can be expelled the quicker it dries.

    I guess you’re talking about floating the plate in your aquarium – I suppose you could do that, but I don’t see much point in it.

    It’s a simulation of when we’re seasteading :-)

    There is also a type of cement called hydraulic cement that can set in standing water, but it costs more. This was what was used when the Chicago River had a leak, almost twenty years ago. It is useful for repairs, but it is more cost effective to use regular concrete in a dry place for initial construction.

    Well I got portland cement, which is at least supposedly the same thing.

    Actually I think it was even cheaper than mortar-cement at the store.

    J.L. wrote:

    It’s possible that the bubbles were trapped, or off-gassed, as cement has an exothermic reaction, as is cures, even if it is a mild one…

    Ya, may have also been that I thoughtlessly used a metal spoon, which pulls water to the surface,

    so it ended up shiny on top, and pocked at the bottom.

    shiny

    Yes, I meant wax paper. One way to do the bowl, would be to shpe if over a shaped mound of wet sand… As for floating, I hear the original cement pirogue is considered water-worthy, in whatever museum it is in… Matter of forming it to displace more water than its’ dry weight, after curing… Basically, don’t make the ‘hull’ too thick, in relation to the desired displacement…

    I made one in the shape of a cup I had.

    For this mix I used 1 part clay, 2 part cement, 2 part sand

    2 tablespoons clay, 4 tablespoon cement, 4 tablespoon sand, 2 tablespoon water.

    As you said with the wax-paper in the middle:

    It does float, but just barely, so I’ll attempt a wider shape next time.

    This time I was molding with plastic gloves and waxed paper, so it’s smooth surface all around.

    By the way, do you know if it’s safe to drink or eat from cement plates/bowls, or drink from cement cups?

    I read online some people have cement dog bowls, but am not quite sure it’s safe for humans.

    calm aware desire choice love express intuit move

    #12010
    Avatar of J.L.-Frusha
    J.L.-Frusha
    Participant

    I would suggest sealing it with a food-safe substance. Portland cement can cause toxicity issues. Dermatitis is common, with skin repeatedly exposed to it, such as hand mixing…

    Later,

    J.L.F.

    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.

    #12015
    Avatar of elspru
    elspru
    Participant

    J.L. wrote:

    Yes, I meant wax paper. One way to do the bowl, would be to shpe if over a shaped mound of wet sand…

    Hey, I tried that, it worked better than expected, though it didnt float, was mainly due to irregularity of the shape.

    here are some pics of it:

    concrete mix was 1:1:1 cement:clay:sand

    this is when it was drying, also with the bowl in plastic container that I covered with oil

    here is the final product

    As for floating, I hear the original cement pirogue is considered water-worthy, in whatever museum it is in… Matter of forming it to displace more water than its’ dry weight, after curing… Basically, don’t make the ‘hull’ too thick, in relation to the desired displacement…

    Ya, I realize I should probably make calculations of how much concrete I need for a given structure,

    Basically this time I had also too much in the bowl, but I took some of the extra off, till I got it floating at a reasonable level.

    I even had the opportunity to level it to make sure it floated similar height on all the sides.

    calm aware desire choice love express intuit move

    #12232
    Avatar of elspru
    elspru
    Participant

    Hey so I made another model,

    one with aluminum modeling mesh for the frame, and galvinized wire to hold it together.

    here I’m demonstrating a boat frame can be larger than the drydock it’s built on:

    Here I added concrete mix several times till I covered the frame:

    I used 125ml cement,

    with calculations based on 120ml
    2/5 cement
    2/5 sand
    1/5 clay
    3/100 baking soda

    with about 1/5 water or a little more

    it ended up being rather heavy,

    though it still floats, it has some leaks,

    from various exposed metal surfaces on the inside.

    so decided to make a larger boat,

    as that would increase the volume to thickness ratio.

    so made one from a larger piece

    made it in an egg shape, with cone shaped bottom front and rear corners, though the front is more vertical.

    I was reminded of bulbous bows

    the following image is from the rear of the boat.

    perhaps the front should have been more bulbous,

    but I was inspired to have a straight front from this bolger box boat

    though also thinking about letting the bow float higher,

    I plastered it with 515 ml of concrete of the same mix

    though it wasn’t quite enough for the bow and transom, I focused on the bottom.

    I tried floating it, once it had dried, though some water leaked in 3 or 4 places

    I was quite happy about how high it was floating however.

    I plastered it with an aditional 260ml of concrete

    calm aware desire choice love express intuit move

    #12235
    Avatar of J.L.-Frusha
    J.L.-Frusha
    Participant

    You might try a bit more water, so it is easier to work into the mesh. That appears to be window screen, which is good. A problem with the expanded mesh plaster lath is the angles create voids, thus weak-spots, where the cement is not in contact with the mesh.

    Later,

    J.L.F.

    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.

    #12258
    Avatar of elspru
    elspru
    Participant

    J.L. wrote:

    You might try a bit more water, so it is easier to work into the mesh.

    I usually add a bit more than 1/5 like 3/10ths.

    also the sand and clay is already wet.

    That appears to be window screen, which is good.

    it’s not, though I guess that’s a good idea.

    it’s actually a flat diamond mesh made of aluminum.

    A problem with the expanded mesh plaster lath is the angles create voids, thus weak-spots, where the cement is not in contact with the mesh.

    ya, that’s likely what’s happening with my boat,

    also it seems as though the baking soda was a bad idea,

    since it all seeped out of the concrete.

    maybe I’ll use some chalk or gypsum powder instead to make geopolymer.

    though really it’s optional, ash is much more requisite, for sulphate resistance.

    would you recomend using galvinized chicken wire for larger models or something else?

    Also I’ve yet to make a boat with an internal frame.

    though might require some welding equipment,

    unless I tie together some metal sticks with wire.

    #12461
    Avatar of shredder7753
    shredder7753
    Participant

    omg – Spruski bought cement

    #12474
    Avatar of elspru
    elspru
    Participant

    shredder7753 wrote:

    omg – Spruski bought cement

    Due to a lack of sand, and thick ice preventing further harvesting till spring.

    yes, my latest experiment was to use a mix of cement and clay.

    first I made a clay slurry, and then I added cement.

    Unfortunately, it’s highly water-permeable now.

    So while it did set very well, and floats high,

    I think I’m getting better at the application technique,

    when I set it in the water, it rapidly starts seeping water.

    maybe i’ll layer it with some pure cement,

    hopefully that will fill in the little air-pockets,

    that formed since probably the slurry was too watery.

    so far, I don’t have a single boat with metal frame operational due to leaking, and cement mix issues.

    I do have a working cement-sand mixed boat I made using a plastic container mold.

    calm aware desire choice love express intuit move

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