12 replies to this topic

[mmcguffi]

I recently poured some plaster into a ~3x3x3 inch plastic container, set up like the authors of this paper demonstrate (Fig. 5D; other figures). After the plaster set, I immediately saturated the plaster by rising it and also filled the water reservoir

 

After ~24 hours, I grabbed ~10 Atta workers from a prolific colony near my house dropped them in. Since then, the worker have hardly been able to walk -- very clumsy and will often flip over onto their backs. They almost look intoxicated. Several of them may be already be dead, but it's currently hard to tell. Anecdotally, it seems like when I open the top to get fresh air in, they all perk up. The plaster also smells very strongly of, well, plaster

 

Well, I am very glad I did this experiment! Something is not quite right, and I'm not sure what it is. I have not read anything about plaster needing to off-gas or anything like that, but if anyone knows more about hydrostone (mostly gypsum with a bit of portland concrete I believe) I would appreciate your input. Or if you have other ideas I would love to hear them too! Also, I highly doubt these ants were exposed to a pesticide or something /before/ I put them in, I feel relatively confident they are reacting to something in my setup

Edited by mmcguffi, January 31 2021 - 8:49 PM.

[M_Ants]

You want to let the plaster cure completely before you add water let alone workers. Just because it has hardened doesn't mean it is cured. You don't want to add either for a while after it sets. Also adding water right after it sets is definitely a bad idea. It probably weakens it and messes up the curing. 

[mmcguffi]

You want to let the plaster cure completely before you add water let alone workers. Just because it has hardened doesn't mean it is cured. You don't want to add either for a while after it sets. Also adding water right after it sets is definitely a bad idea. It probably weakens it and messes up the curing. 

Interesting, I must have missed this when researching -- thanks! This pottery forum thread seems to indicate that it takes ~30 days for plaster to fully cure, which /feels/ a bit overkill to me? But I also have no intuitive understanding of what is causing the issue here

[M_Ants]

The chemical processes that occur that make plaster safe to use take a while. 30 days is overkill but it really depends on how much you're using.

[AleeGuy]

it is probably because the plaster wasn't completely cured enough. I doubt that the reason is that it is toxic. Were you using gypsum cement, or plaster of paris? And just to make sure, what brand did you bought the plaster from?

Edit: sorry, you replied to some of the questions already. The other posts loaded after I posted this one.

Edited by AleeGuy, January 31 2021 - 9:14 PM.

[ANTdrew]

I would give it a minimum of ten days curing time.

[Spazmops]

If you're using gypsum cement (hydrostone), depending on the quantity that only takes a few hours. I've put ants in hydrostone nests the day after it was completely solid to the touch and they were fine. 

[Cephalotus]

I've cast, carved with a Dremel, and put ants in a hydrostone nest all within an hour and they were fine. I wouldn't take this as evidence though that you don't need to let it cure.

[mmcguffi]

I let it harden/cure for about an hour before saturating it with water. Can anyone give insight as to what chemical and or physical process(es) happen when hydrostone -- or gypsum plaster in general -- "cures" over several days? As far as I can reason, this is just the process of excess moisture leaving the plaster, which increase compressive strength within the plaster (I'm not 100% sure why that would increase tbh). As far as I know, the crystals form just after the plaster becomes hard -- this is why it then heats up, as the molecules find a more organized state to exist in and convert the decrease in internal entropy into heat. I don't think there is any "long term" chemical reaction taking place here, but if anyone knows more about gypsum chemistry (and/or portland cement chemistry) I would love to hear from you

 

All of that said, why would one need to wait ~10 days or whatever in order to just re-soak the plaster? Other people in different industries/hobbies want the moisture gone before they use it, but that is the explicit opposite of what we want

 

In any case, I will probably caste a new one and let it sit for a couple of weeks before I hydrate and see what happens

[Spazmops]

I let it harden/cure for about an hour before saturating it with water. Can anyone give insight as to what chemical and or physical process(es) happen when hydrostone -- or gypsum plaster in general -- "cures" over several days? As far as I can reason, this is just the process of excess moisture leaving the plaster, which increase compressive strength within the plaster (I'm not 100% sure why that would increase tbh). As far as I know, the crystals form just after the plaster becomes hard -- this is why it then heats up, as the molecules find a more organized state to exist in and convert the decrease in internal entropy into heat. I don't think there is any "long term" chemical reaction taking place here, but if anyone knows more about gypsum chemistry (and/or portland cement chemistry) I would love to hear from you

 

All of that said, why would one need to wait ~10 days or whatever in order to just re-soak the plaster? Other people in different industries/hobbies want the moisture gone before they use it, but that is the explicit opposite of what we want

 

In any case, I will probably caste a new one and let it sit for a couple of weeks before I hydrate and see what happens

I'm a little confused. Are you using gypsum cement, or plaster of paris?

[mmcguffi]

It's in the title and even expounded upon in my text -- Hydrostone, which is gypsum plaster with a bit of Portland cement.

[NickAnter]

Could it possibly be the container that they are in? Maybe do some tests with that.

Edited by NickAnter, February 1 2021 - 8:55 AM.

[mmcguffi]

So I'm still not sure what the issue was, though allowing it to "cure" (just sit without water) for about a week before I hydrated seem to do the trick. Maybe this is due to the pH drop that happens as concrete cures? I'm not sure

 

I have new workers in the "cured" plaster container, and they look fine. I waited until the plaster stopped smelling... like plaster ...and then I hydrated it.  Moving forward I think I will probably try to cure my other formicaria for at least a couple of weeks before adding ants, and ideally the full month that the pottery forum I posted above mentions