How Long Does It Take Plaster To Harden?

[kolleamm]

last time i used plaster it never hardened, it just sat there for hours, since im going collecting tommorow im curious to see if anyone has any advice on using plaster.Also what do you recomed covering the fossil with before applying it. Can someone just explain to me how to plaster a fossil LOL should have written that from the start.

Edited June 19, 2010 by kolleamm

[bear-dog]

To plaster a fossil you start with a quart of Tequilla.... Oops thats how to plaster a fossil hunter :lol:

The problem you encountered was probably using too much water.I like to mix it like pancake batter,maybe a hair thicker.Before making the plaster jacket,I usually place aluminum foil on it to prevent sticking,and maybe a layer or two[optional]of newspaper as a cushion.

In the future you may want to check out hospitals dr. offices ,etc to purchase outdated casting material.They usually write it off and toss it.Store it in zip lock bags for later use.Just soak and use.

Hope this was useful. :beerhat:

Edited June 19, 2010 by bear-dog

[Auspex]

Sounds like it was too old; just a little atmospheric moisture and a little time will ruin it. Get some fresh, and use it up.

[Matt Kapraun]

also you could try using warm water speeds up the set time of plaster or add some salt or vermiculite also speeds up the set time.

[dinodigger]

last time i used plaster it never hardened, it just sat there for hours, since im going collecting tommorow im curious to see if anyone has any advice on using plaster.Also what do you recomed covering the fossil with before applying it. Can someone just explain to me how to plaster a fossil LOL should have written that from the start.

Hey, I hope this helps. We use plaster in the field, more specifically, we use Hydrocal. Its a harder plaster. If you go to an art store or a pottery supply store, you will notice that there are different grades of plaster. Avoid the basic plaster, or the bottom of the line plaster. Many things can go wrong with it. More on that in a second. We've always buy out the store with Hydrocal. Drys quick and is very hard. If you can't find that one, get pottery plaster. Its a lot harder than the basic stuff. In the field, we always have a pretty good recipe to abide by. Always use hot water if possible. Pour salt in the water before you add the plaster, mix it up well. Then add the plaster. The salt helps quicken the reaction with the water. You'll feel the plaster get really warm when its starting to set. Another thing to remember is never add water to plaster, only plaster to water. That is, when you are adding the plaster to the water, never mix, then add water. Completely ruins the reaction for some reason. Dilution takes effect. When mixing in the plaster, we always do it slowly at first. One handful of plaster, mix by hand to get out the lumps... etc. With our five ton dinosaur jackets we use a big electric mixer. But for the small field jackets under five hundred pounds we do the slow mix. Learning when the consistency is right is always hard at first. Typically we like the pancake syrup thickness as a sign were ready to go, or close, depending on the type of jacket. So why didn't the plaster work? Couple of things go wrong, we see it in the field a lot. When plaster sits un-used for a long time, or it is exposed to the elements for a while, it can go bad. It can rot. Old plaster just goes bad. We have that problem with baseline plaster when we cant get hydrocal. Going with that or the good pottery plaster lessens the chances of bad plaster. And again, if plaster has water in it and it dries, then it often rots. Can't see it, but you know it when you are pulling your hair out waiting for it to dry. Another problem we noticed is the water. If the water is soapy, then the plaster won't mix. The small towns we camp out in on our dinosaur projects have well water that doesn't work great for plaster, so we often have to use good bottled water to get a good plaster mix.

Covering the fossil: we always cover the specimen in a thick blanket of foil. Good for protection from the elements and also keeps the specimen from drying out and cracking. When working with a smaller jacket, we like to make easy open lids with the plaster, so when we get them back to the lab, the opening part isn't as annoying. Foil and plaster, then a foil separation plane on top, and a kettle-top plaster lid. Easy open...

Anyhoo, hope it helps. Good luck. Don't eat the plaster. Unless your that kind of guy.

Chris Flis

Edited June 23, 2010 by dinodigger

[jpc]

I also think your plaster was old. I have used plain ole plaster of Paris for years and never had any problems. Sometimes it takes longer to set, bu I usually have the time to wait, or go find the next cool fossil around the corner while it sets. I have friends who are big fans of hydrocal and used it once in the field with one of them. It does dry quickly and hard.

Meanwhile, I'm intrigued... what did you go collect? How did it go?

Edited June 23, 2010 by jpc

[Xiphactinus]

Hey, I hope this helps. We use plaster in the field, more specifically, we use Hydrocal. Its a harder plaster. If you go to an art store or a pottery supply store, you will notice that there are different grades of plaster. Avoid the basic plaster, or the bottom of the line plaster. Many things can go wrong with it. More on that in a second. We've always buy out the store with Hydrocal. Drys quick and is very hard. If you can't find that one, get pottery plaster. Its a lot harder than the basic stuff. In the field, we always have a pretty good recipe to abide by. Always use hot water if possible. Pour salt in the water before you add the plaster, mix it up well. Then add the plaster. The salt helps quicken the reaction with the water. You'll feel the plaster get really warm when its starting to set. Another thing to remember is never add water to plaster, only plaster to water. That is, when you are adding the plaster to the water, never mix, then add water. Completely ruins the reaction for some reason. Dilution takes effect. When mixing in the plaster, we always do it slowly at first. One handful of plaster, mix by hand to get out the lumps... etc. With our five ton dinosaur jackets we use a big electric mixer. But for the small field jackets under five hundred pounds we do the slow mix. Learning when the consistency is right is always hard at first. Typically we like the pancake syrup thickness as a sign were ready to go, or close, depending on the type of jacket. So why didn't the plaster work? Couple of things go wrong, we see it in the field a lot. When plaster sits un-used for a long time, or it is exposed to the elements for a while, it can go bad. It can rot. Old plaster just goes bad. We have that problem with baseline plaster when we cant get hydrocal. Going with that or the good pottery plaster lessens the chances of bad plaster. And again, if plaster has water in it and it dries, then it often rots. Can't see it, but you know it when you are pulling your hair out waiting for it to dry. Another problem we noticed is the water. If the water is soapy, then the plaster won't mix. The small towns we camp out in on our dinosaur projects have well water that doesn't work great for plaster, so we often have to use good bottled water to get a good plaster mix.

Covering the fossil: we always cover the specimen in a thick blanket of foil. Good for protection from the elements and also keeps the specimen from drying out and cracking. When working with a smaller jacket, we like to make easy open lids with the plaster, so when we get them back to the lab, the opening part isn't as annoying. Foil and plaster, then a foil separation plane on top, and a kettle-top plaster lid. Easy open...

Anyhoo, hope it helps. Good luck. Don't eat the plaster. Unless your that kind of guy.

Chris Flis

I like hydrocal, but if you are prepping your fossil where it will be on the plaster as a background (like we do with the Kansas fish) I do NOT recommend hydrocal. Like you said, it's hard! I used it once and prepping the background took forever because the stuff was like limestone!

[JimB88]

I think it depends on what your collecting as to whether or not you even need plaster. The few times ive used it its been the plaster bandages (just dip em' in water and apply) over tinfoil (put the tinfoil on first, then the plaster - makes it easier to remove the jacket.)

[Alan]

If you feel a need to make a field jacket, first consolidate the specimen -- only if necessary, if it is falling apart -- ideally with a proven reversible adhesive (Paraloid B72, Butvar B76; white glue and super-glues, cyanoacrylates, are not reversible). Then cover the entire block, not just the fossil, in damp toilet paper or paper towels. If you only cover the fossil you risk the plaster sticking to the matrix and causing damage to the fossil when you remove the jacket. As described above, you can also use aluminum foil as a barrier layer, which will seal in moisture. If your jacket will sit in storage for a long time this might not be such a good idea as mold might grow in the jacket. Damp paper will dry out over time.