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Thread: Cement rocks and stuff

  1. #1
    DIYFK member trachr's Avatar


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    Cement rocks and stuff

    So i was curious, how practical would it be to use cement to make large rocks and such, as in build a form, poor some in add color and come out with a good looking sturdy cave or rock etc.

    I figure it would have to be solid or made out of foam and cement with the foam having holes in it so it would be more cement than foam...so it wont float away

    This practical? And what would you use as form material so it could be reused.

    Also if i did use foam boards, is holowing out parts the only real way to keep it from floating? I dont want to have to silicone it down.

    Bte these are 2 seperate ideas lol, solid cement for rocks and such...and i was lookin at foam with cement coating for larger things...sandfalls and such


    Thanks

  2. #2
    DIYFK member Meep's Avatar


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    Molding is generally more trouble than it's worth for this application... It can be done but molds can be costly to make especially for one offs... Instead you can do hollow castings using paper mache techniques, but instead of paper and flour paste, use burlap/fiberglass strands/milled fiberglass and a Portland cement and sand mixture... The surface can be finished in multiple ways with another layer of the Portland cement and sand mixture, using brushes or other pattern tools and misc pigments to give it a realistic look... This is how all those fake rocks, rock walls and sorts at zoos and amusement parks are made...

    If you make them hollow just get a concrete drill and drill a small hole up top this will let all the air out and sink to the bottom...

    You can also form over styrofoam and when you are done take a propane torch and simply burn out all the foam, take acetone and melt out all the foam, or chunk it all out... Just be sure to soak and cure the concrete afterwards to get rid of any residue...

    Another way is to make a form out of foam and then cover it with some synthetic fabric (nylon, polyester) then do the build up on that, this way when you flip it over the fabric acts as a mold release you can more easily remove the foam as it won't stick to the cement, and you can leave the fabric when you are don, thus the reason for synthetic is so that it doesn't rot in time... Or instead of fabric to cover your mold you can also use plastic sheeting or plastic wrap, you should be able to remove most of that when done...

  3. #3
    DIYFK member trachr's Avatar


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    Thanks ill have to give that mache thing a try. As for 1 off things, some things i suspect i will want to make multiples, as you may remember i have some simple caves that local ppl buy from me...not for tons but it is helping me support my hobby... but i was thinkin if i could make a sandfall, which ofc wont be a simple thing like my caves but i suspect a sandfall would sell well..

    So that means complicated... thats really where the molding idea came from...once i figure out how to do it i will want to do it quick and as easy as possible. Not to mention cheap if i sell em.


    On a side note once i figure these things out i plan on doing a 125 similar to that avatar tank...google it if you havent seen it... its nice lol

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    DIYFK member daFrimpster's Avatar


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    You will need to cure the pieces or seal them if you use concrete. Otherwise your PH will skyrocket when you add them.

  5. #5
    DIYFK member Meep's Avatar


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    I just remembered another way to make a rough shape to build off of, take some plastic canvas and using either zip ties or fishing light cut and tie it together to make a mesh frame to lay the cement mache over...

    For the cement mixture use 1 part Portland Cement to 3 parts fine sand as a starting point, you can adjust it up and down a bit but that is pretty much ideal for this purpose...

    As for molding there are lots of tutorials for concrete molding on Youtube, but as I said it's costly... I have done a great deal of molding and know how to do it well, but there is a learning curve and mistakes can be costly...

    Generally for concrete you are going to want a latex or urethane rubber mold, latex is a little cheaper but the mold won't last as long...

  6. #6
    DIYFK member trachr's Avatar


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    Ok, thank you... if i try to mold the stuff i will do alot of expect a lot of questions lol


    Ill give that canvas thing a try

  7. #7
    DIYFK member trachr's Avatar


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    With cement color is the liquid color the best or are the powder colors ok too?

  8. #8
    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by trachr Click here to enlarge
    With cement color is the liquid color the best or are the powder colors ok too?
    I personally prefer powdered pigments as they are generally stronger and easier to store, and cheaper to ship... One thing to note, don't waste pigment on the first layers, just pigment the top layers... You can also sprinkle and/or dust the powdered pigment on the still wet concrete to get further color highlights...

  9. #9
    DIYFK member murphyg27's Avatar


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    After being away from the hobby for many years I am coming back and need a bit of expert advice, I got a decent 125 gallon tank pretty cheap, cleaned it up and all looks great, built a ridiculously strong stand with 8 4 x 4 s and 2x6 s and am in the process of creating Joey's brilliant led light system, after already doing his bucket canister filter.
    Now is the background issue, I would love to do the cement styrofoam background but as per Joey's advice find that countless water changes for up to eight weeks tough to pull off as I don't have a backup tank nor much space for one.
    I saw a background build where spray styrofoam insulation material was used, large amounts of sand added while wet, and caves also created. This looked pretty good too. This build said to use spray polyurethane as a sealant for the whole project and waiting several days for the poly to cure.
    It occurred to me that it might be possible to make Joey's wonderful cement version, wait several days, then poly the cement version to seal everything.
    Has anyone tried this speed up version or had any other speed up version suggestions for Joey's cement version. I inherited a couple of pretty nice fish and don't want to kill them off through some wreckless stupidity. Thanks


  10. #10
    DIYFK member Meep's Avatar


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    The problem with clear coating cement is that cement literally take about 30 days to fully cure, thus you have to wait that 30 days or risk trapping in moisture that will cause the clear coat to fail...

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