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View Full Version : Portland vs. Plaster

brideauj
11/18/2002, 12:11 PM
Not to strong on Chemistry but has anyone tried making home made live rock with plaster of paris instead of portland cement. I would think the clean white would be more visually appealing (at least to me) untill it gets covered in purple.

Portland is a mix of calcium compounds from what Iwas able to find and plaster is just calcuim sulfide, one of the many components in portland.

Cheers
MarkS
11/19/2002, 02:14 AM
Plaster softens once it gets wet. Cement does not.

Mark
Zephrant
11/20/2002, 12:02 PM
You can also get white portland cement. You may have to go to a shop that specializes in cement products though- Here in Spokane, the place is "White Block". I'm sure you have some place similar.

Zeph
Salt Creepy
11/20/2002, 02:18 PM
Back when I was getting into model railroading I bought a bag for landscaping that looked almost exactly like plaster of paris but it set up much, much harder. That was a long time ago and I can't remember what it was. Does anyone know what that might have been?

I put a piece of hardened plaster in RO and after one day the TDS was almost 1000. I don't think P of P will work.
brideauj
11/20/2002, 02:27 PM
I bought a $5 box of tile mortar from Lowes. It is a polymer/portland blend and is "pure white". I made a test rock and have it sitting in vinigar and water overnight and will see how it works out. I plant to soak it in fresh water for a few weeks. I thought about letting it sit in the Atlantic for a few weeks since I am within walking distance but by the condition of my lobster trap ropes after a few weeks, I would be scraping green crud off of the rock i'm sure...
Zephrant
11/20/2002, 11:12 PM
Creepy- I think you are thinking of "hyrdocol", which is a type of plaster that does not shrink/crack when it dries. It is commonly used with rubber molds, i.e. making rocks for train sets. :)

I've also had some success in using it to mold fiberglass parts for RC airplanes.

I'm not sure it would stand up to saltwater though... and it is pretty expensive when compared to white portland cement.


Zeph
Salt Creepy
11/21/2002, 12:57 PM
Zephrant,
That rings a bell, thanks