I am going to be using a scenic express rock mold (the big size) as a base to hold a 1/6 resin figure. How do I make the plaster of paris stronger so that I can peg the figure to it and the plaster of paris to a base without it crumbling/cracking?

Can't tell you how to strengthen POP by I can recomend a better product.
Aves Clayshay is a fantastic product.
Rick Brownlee the Miami-jayhawk turned me on
to this stuff and it is really great. I've cast 8-9 rock castings from rubber molds using Clayshay and it is much lighter and stronger than POP.
You can order it online from Aves.
Best regards,
Gary

Maybe some reo? Think it is re-bar "over there" but if you could use some small reinforcing wire to be set inside the pour just like in real concrete pouring?
Maybe?
Cheers
Brad

Window screen might help too (acting like Mesh in concrete)

you can add fibre glass to it as well but it would be easier to do it one of two ways.

A/ srew up a small amount of wire netting and place this in your POP

B/ get some gauze bandage and soak it in your POP and then wrap this up. This will make a similar type of plaster bandage that the hospitals now use for holding broken arms and legs while the bones set.

Cheers
Cliff

Hi Godfather,
when I'm pouring walls out of P.O.P., I usually add some liquid tile grout colourant into the water before adding it to the plaster.
I basically get my stuff ready to go, and I have my jug of water, then I add the colourant to the water, thourougly mix it , and add it to the plaster. I find it strenghtens the plaster considerably when completely dry. You can get the liquid colourant at any home center.

OH: IDEA!! Although I have not tried it, I just thought, you could try adding some non-sanded tile grout right into the plaster powder before adding your water, I bet that would strengthen it pretty good as well!
Cheers,
Kelly

Another alternative is to mix some pva glue into the plaster whilst mixing it. One thing though - get it into the mould quick!

Plaster comes in many different types. General purpose plaster of paris is the weakest amounst them. What you want is called Improved Stone, or even Die Stone. You may find what you need in an art supply house, just tell them you want a plaster with a greater compressive strength.

Try this: http://www.pearlpaint.com/shop~ocID~2999~parentID~2961~categoryID~2956.htm

or This: http://www.pearlpaint.com/shop~ocID~2999~parentID~2961~categoryID~2953.htm

Plaster of Paris is generally fairly strong unless the mix had too much water in it. However, it has very very poor flexibility and cracking occurs if its bent even slightly. First off having a firm base to lay the plaster on is important. Solid wood is good and plywood okay. The latter needs to be varnished to reduce the chances of warping and causing the plaster to crack.

Add a bit of fine sand also helps to the plaster slurry. Its a bit like cement which is strengthened by the addition of fine sand.

I have another alternerative to POP. IF you use something called Herculite Plaster or dental plaster which is stronger but may cost a little more



http://cgi.ebay.co.uk/HERCULITE-2-CASTING-PLASTER-1-5kg-mould-moulds-mold_W0QQitemZ8248193441QQcategoryZ3090QQrdZ1QQcmdZViewItem

I build a lot of dioramas and I would never use plaster for anything. I would use epoxy putty as it is the strongest material available and it would be quite easy to fill a rock mold with it. Once dry you can sand it, drill it or carve without any fear of cracking or crumbling.