Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Problem with corrosion of gypsum cement

  1. Jan 22, 2015 #1
    Hi, I have been working on a formicarium (terrarium for ants) design for a while now, and have been battling a problem with what I think is corrosion of gypsum cement. This design has a hydration system that basically uses capillary action to wick water up a sponge and into gypsum cement (Hydrostone to be exact). What happens, is in just a matter of hours, the sponge or any other material litterally eats its way into the Hydrostone, and sometimes I actually find pin holes all the way through 1/4 inch of it.

    This is what this particular formicarium looks like. This is the one mostly affected by this problem.

    med_gallery_2_281_430580.jpg


    This is what the top (floor of the top container) looks like after eight hours or so.

    med_gallery_2_281_415442.jpg


    This is the bottom of the top container (directly below the hole in the first picture). This is what actually sits on the sponge.

    med_gallery_2_281_500747.jpg


    This is the bottom magnified.

    med_gallery_2_281_151665.jpg

    Hydrostone is made up of >95% Plaster of Paris, <5% Portland Cement, and <5% Crystalline Silica.
    The MSDS can be found here: http://www.usg.com/content/dam/USG_...ydro-stone-gypsum-cement-msds-en-52140052.pdf

    The water used is typical bottled water.

    Quite a few people I know have suggested this could be a pH issue causing calcium to dissolve.

    If anyone can tell me what might be happening here, and if there's a way to stop it, it would be much appreciated.
     
    Last edited: Jan 22, 2015
  2. jcsd
  3. Jan 23, 2015 #2

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Not a pH problem. Plaster of Paris dissolves in water.
    The water is just to control humidity for the ants? Not an actual source of drinking water? If that's the case, saturate the water in the tray underneath with broken hydrostone plates, or plaster shards. No concentration gradient in the wick, no transport of dissolved gypsum down the wick to the water tray.
     
  4. Jan 23, 2015 #3
    Interesting. The water actually serves both functions. The particular type of ants that this specific formicarium is for, are called Leaf Cutter Ants. They garden a type of fungus that requires near 100% humidity at all times.

    For the sake of not complicating the post too much, I didn't mention that I actually tried something much like what you just suggested, except I was doing it in hopes to balance the pH. I poured a 1/8 inch layer of Hydrostone in the bottom of the water tank, which seemed to have solved the problem at first. The only thing is when I did this, because the tubes that support the sponge were so close to the bottoms of the tanks, this left a very small crack to allow the water to flow through to the sponge, that it slowed down the rate of absorption. Once I modified it to allow another 1/8 inch of clearance again, the rate of absorption was back up, and the holes started to form again. I'll still try exactly what you mentioned, but do you think maybe actually pouring some Hydrostone while still in powder form into the water would do the same? Also, wouldn't it be possible to put water filters on the ends of the tube supporting the sponge so that it would only have to saturate the water in the sponge?
     
    Last edited: Jan 23, 2015
  5. Jan 23, 2015 #4

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    It's IN solution --- no filter for that. The sponge/wick is going to be a substrate for the fungus isn't it, so you have to have something between it and the garden. Any "Hydrostone" mixes that are higher in cement concentrations?
     
  6. Jan 23, 2015 #5

    Stephen Tashi

    User Avatar
    Science Advisor

    dspdrew,

    Why is Hydrostone (other than the errosion problem) a good material for your design? Why not concrete or terra cotta?
     
  7. Jan 23, 2015 #6
    Yes, UltraCal 30 has roughly double the portland cement, according to the MSDS.

    It probably wouldn't be too difficult to make a custom blend, given the simplicity.
     
  8. Jan 23, 2015 #7
    Up until now I thought Hydrostone was mostly concrete, but now that I know it's not, concrete does sound like an option. Terra cotta, or other clay-based materials would work great, except they either need to be fired, or if they're already fired, they would need to be cut and fit into the containers, which would not be easy. However, a bisque or unglazed ceramic tile was actually my next best solution; I just wanted to make sure I wasn't overlooking something about the Hydrostone that could be easily fixed. At this point, it doesn't sound like it can be, so I probably will go with the ceramic tile, but first I do want to explore the concrete idea.
     
  9. Jan 23, 2015 #8

    Stephen Tashi

    User Avatar
    Science Advisor

    Thin slabs of ordinary concrete tend to crack. If you need thin slabs , try the type that's made for leveling floors. You can find concrete reinforcing fibers for sale on Amazon and they are useful for thin slabs.
     
  10. Jan 23, 2015 #9
    Thanks everyone for your help. I'll give these ideas a try and let you know how it turns out.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Problem with corrosion of gypsum cement
  1. Copper corrosion (Replies: 14)

  2. Corrosion of pipe (Replies: 1)

  3. Corrosion and rust (Replies: 7)

Loading...