What material should I make a mold for my building out of and what should i use to make the walls?? I thought plaster of paris but it warped my posterboard mold, An ideas would be helpful I'm looking to get this diorama started on and in notable progress by next week, Any thing ya got will help thanks in advance

Wood would work for a plaster mold. seal it with Polyurethane (on all sides). A cookie sheet would work too.

I didn't make it as a mold but if i was to do it should i cutout the inside or just pour the plaster over it an sculpt it?? What other materials could i use to make a mold??

Use a board and build a "dam" around it to pout the plaster into. It would look like a box with the top cut off.

Here is one post that shows how to make a mold for a wall. It's rather ingenious and uses materials that you have at home. I think its what Matt is getting at too.
The other way to make a mold for plaster is to use latex. Woodland scenic has nice latex product that I use. I don't know how well the posterboard is going to stand up to to the latex. The latex goes on wet and drys to a reusable mold.
If you want to reproduce wood grain in the plaster the best thing to mold is wood. Make a wall out of bass wood and mold that. Then pour the paster multiple times to get more than one wall.

And with this I bump to Lt. General!!!!!!!!

Using latex to make a mold is a pretty good idea. I have done a few to duplicate various Verlinden plaster buildings. One thing I have learned from using latex is that by itself it is not very strong and it rips easily. Good way to make is tronger is to apply medical gause inbetween latex layers. This will make it virtually tear proof.

Hey Scott, I salute you LT. General. Congrats! I hope to some day get to your rank as well.

Go to the Home Depot or similar store and buy a glazed ceramic tile. You can then hot glue some 1x1 to the edges and have a mold box. When you are ready to unmold your piece, remove one of the edge boards and slide the plaster out..

Whenever I need to make a mold (and I do a LOT), I look for clear plastic lids that come on toy boxes, veggie trays, sweet rolls etc. I keep a large box full of them in my studio... they are free, available in every imaginable shape and size, and once you are done, you can just clean and re-use, or chuck it into the trash bin!

But do the edges where they connect seal tight enough to prevent the plaster from seeping out while it dries?? KFMagee are you talking about those foamish like trays that come with the veggies at the supermarket?? those work?? they're not too pourous?? thanks to all for the help please contineue to contribute

If you use double sided tape, there should be no problem. Even if there is a tiny leak, it shouldn't result in too much flash. After all, you are going to have to dress the edges to get a true 90 degrees.

Thank you for the help

No sniper... I mean the ones that are usually CLEAR hard plastic - usually with a BLACK bottom section... but the styofoam type may also work.

Okay - here is another idea I have used. Get a LEGO set - it usually has a FLAT GREEN base that is around 6 x8 inches. Use other lego bricks to form a 'dam' around the green base. Then use old fashioed modeling clay to lay a smooth layer across the bottom of the green base, thus hiding the peg bumps. If you want, you can even use a wooden rectangle to make impressions for bricks or beams. Now you can pour in your plaster. Once it dries, just pop loose the side dam, and pull out your plaster wall.

Now if you look at the walls and things I sell on my website, those are all hand-carved first into BALSA FOAM, and then a mold is made with RTV Silicone Rubber - but it is not worth this method unless you intend to sell dozens of reproductions or else you will have paid $20-30 just to create a single mold!

Does this help?

While we're on the subject of plaster casts... what water to plaster ratio do you guys generally use?

Another good question, I can't seem to get it correct with the dirctions on the package it's too powdery and crumbles too much

I've used plasticene to make moulds. This works ok if you're making sections of cobbled street for example. Plaster of paris is then poured in and a ruler or straight edge is pull across it to flatten it out. To give it a bit more texture you can mix in some vey fine sand. I've had more success with plaster as its a little more substantial and has some sand mixed in.One thing you can use to make a deeper mould is lego bricks although this is better for smaller items using resin....Jim #:-)

Sorry without realising ive just copied the previous post...My apologies #:-)

okay so i've scrounged around my home for any materials my wife deems trash and come up with some good wood. ive nailed it together like a box, but there are some spaces in it, would hot glue work to fill these gaps??? do i really need to use a polyurathene on it that stuffs expensive

I use an aluminum plate that I got at work to make my sheets of plaster and then carve the detail into them. If you are going to use wood you will need to put something on the mold to keep the plaster from sticking to it. Try some WD 40. Plaster is very good at reproducing fine detail so when you demold the plaster it is going to look exactly like the wood you made the mold out of. You may want to try the ceramic tile idea. Hot glue or super glue the wood to the tile, hit it with some WD 40, and pour away. I have poured plasters of patterns at work and if you don't use something to keep the plaster from sticking to the mold you will never get it plasster out/off of the mold. Trust me, I learned the hard way... #:-) :-)