# Plaster of paris for background?



## shea_and_ruby (Jul 8, 2011)

So, went to bunnings to get the mortar and was told that it would take a few weeks before we could paint over it. issue is that hubby wants this thing up and running asap as he needs to go in for surgery shortly. will plaster of paris do the same thing? has any one ever used this to create a rockwall for the tank? pros and cons or just totally unusable? thanks


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## MSD Reptiles (Jul 8, 2011)

Im not sure about plaster of paris, but im guessing it would create a lot of weight as well?

Im going to try using chicken wire to form the shape then paper mache it to create a solid. Ive then got Pondite to finish it off.... im hoping that should do the job (any feedback or suggestions welcomed).


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## 1woma (Jul 8, 2011)

I use acrylic render, only $10 for 20kilos. never tried plaster


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## Caledo (Jul 8, 2011)

Ive used Plaster of paris on a backdrop. Over paper mache. As long as you apply it think enough so that it wont crack and waterproof you should have no problems. I added cement colour to mine so i didn't have to paint. Was dry in a few hours with no smell.


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## BigWillieStyles (Jul 8, 2011)

I have also been thinking of experimenting with plaster of paris. I wonder if it would hold up in moist conditions and be a bit stronger than polystyrene


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## J-A-X (Jul 8, 2011)

the only trouble with plaster of paris is that it will crack if not applied thickly enough, it will go off (hard) pretty quick too, so you'll have very little time to mould anything if thats what you want to do, 
Plaster of paris on paper mache works well but you MUST make sure all the paper is totally dry before sealing it of or it will rot underneath and eventually collapse. Over chicken wire (no packing under the wire) it would be hard to get the plaster to hang on to the wire and even if you did you'd have to do multiple layers to get some decent strength to a hollow object.

Its great where a smooth 'non rock' look is wanted, i've used it over the top of render to get a really smooth look and the coats only need to be thin so they dry really quick.

@bigwilliestyles, unless its sealed it wont be any good wet (thats why they use garbage bags over broken bones while showering) 

Polystyrene on its own isn't strong thats why most of us use several coats of render to strengthen it, using the foam is just a kind of form work, to support the render.


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## James_Scott (Jul 8, 2011)

I did a silicone cast from a rock and used plaster of Paris for the mold. It worked perfectly. I then used liquid nails and glued it to 4mm back board and it looks great. I would love to get my hands on enough 100% silicone to make a full background and highly recommend plaster of Paris as a medium.


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## J-A-X (Jul 8, 2011)

James_Scott said:


> I did a silicone cast from a rock and used plaster of Paris for the mold. It worked perfectly. I then used liquid nails and glued it to 4mm back board and it looks great. I would love to get my hands on enough 100% silicone to make a full background and highly recommend plaster of Paris as a medium.



was that a fairly flat background or the full on 3D type, it would be weighty as a 3D one


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## shea_and_ruby (Jul 8, 2011)

thanks guys. he went and got some acrylic render, so we'll see how that goes.


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## 1woma (Jul 8, 2011)

make sure you mix some PVA glue in the first coat or two to make it stick to the foam


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## shea_and_ruby (Jul 8, 2011)

oh cheers thanks 1woma


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## MSD Reptiles (Jul 8, 2011)

1woma said:


> I use acrylic render, only $10 for 20kilos. never tried plaster



Thats a whole lot cheaper than Pondtite!!!!! 

Is it available at Hardware stores or is it an art supply?


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## 1woma (Jul 8, 2011)

you'll still need pondtite over the top


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## J-A-X (Jul 8, 2011)

The colored pondtite is expensive and I wouldn't do a whole large enclosure with it but definitely use a few coats of clear to seal it with. The render is normally found with the bags of cement in bunnings


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