Washing the mold. Click on the video on the right to watch it.
This video shows how to wash out the mold before your first casting.
When you first receive your molds in the mail, you will notice they have a fine white powder on them. This is simply baby powder (corn starch). This keeps the molds from sticking together when they are shipped.
This coating of powder will make your very first cast come out badly because it keeps the plaster from flowing into the small details.
To remedy this, take the molds and wash them off completely in the sink. A forceful jet of running water aimed at the pockets in the mold will help wash the powder out of the details.
I have noticed the quality of your castings will become better and better the more you use the mold.
Setting up a work area. Click on the video on the right to watch it.
This video shows what a normal casting area looks like and what kinds of tools you will need for casting.
This is the way that I have arranged my work area. It doesn't take a large space but it's handy to have all the items you need close by. I sit in the center with my casting material on the right and a low trash can on the left. Here's a list of the items I have on hand:
A casting material.
Trash bag to cover your work surface and a roll of paper towels.
Silicone mold and a pounding board of some kind to remove air bubbles.
A metal scraper, mixing spoon and kitchen timer (timer is optional).
A spray surfactant or debubblizer of some kind (optional but highly recommended). Look at How to use surfactant for more information.
a reusable measuring cup (shown above) and extra plastic cups.
The pound board (#5 above) can be made from wrapping a thin hard back book in a trash bag.
You can also take a smaller hard back book and put it into a gallon sized zip-lock freezer bag instead.
Just make sure the book is large enough to hold a mold with a little extra room around the outside.
Sprinkle the plaster powder into the water, let it soak in, then sprinkle more in. As more plaster sinks to the bottom, it will start to pile up. Keep adding until you see a lumpy texture form on the surface.
On the close-up photo you'll notice that the plaster no longer sinks into the water but that the water is soaking up into the dry lumps above the water line. What you see here is just about right.
By nesting this cup back into our measuring cup, you will notice that the plaster is now sitting at the 3.5 ounce mark.
So if you have trouble adding powder by eye, simply add powder until you get to the 3.5 ounce mark and your mixture will be about right. Mix this well using a spoon.
Pouring the plaster. Click on the video on the right to watch it.
This video demonstrates how to pour the plaster into the mold, remove air bubbles and scrape the mold flat.
Mix this plaster up well using a spoon.
Spray the face of the mold using the surfactant you have mixed up.
The surfactant will help the plaster slide into all of the details of the mold and also help bring air bubbles to the surface.
Set the mold on the pound board. This is the hardback book you have wrapped in a trash bag. The pound board is item #5 from setting up a work area shown in the information two sections above this one.
As you pour the plaster into the mold, you will notice that it will be fairly thick and not want to flow into the mold very well.
Don't worry about this just yet. If the plaster were any thinner, you would have very weak blocks that would crumble when trying to remove them from the mold.
Smack the pound board sharply down onto the table top. It works best if you can get a nice flat contact between the board and the table top. Also try to keep the mold level while you are doing this.
With just one tap you will see the plaster flow down into the mold and bubbles will come to the surface.
Continue to tap the covered book onto the table top to release more air bubbles, maybe 15-20 more times. Don't do this so hard that plaster flies out of the mold. You will continue to see more bubbles come to the surface.
Another method is to extend the bottom half of the book off of the table top.
Then tap underneath the book using the handle of a large screwdriver or something that won't damage the book.
You can scrape the mold immediately if you like. However, If you let the plaster set in the mold for 3 minutes, it will thicken up a little and scrape more level.
Plasters may vary, so occasionally poke the corner of the plaster with the putty knife to see how thick it is. If it's the consistency of soft serve ice cream, then you will be able to get the tops of the mold more level and flat.
I'm using a 6" wide putty knife to scrape the top of the mold. I like metal ones the best. You can find these in the paint department of most hardware stores.
Start by holding the knife at a 45 degree angle to the mold and work across with a zigzag motion across the top of the mold. This will loosen up any thick plaster that may be stuck onto the surface of the mold.
Next, hold the knife at a 45 degree angle to the surface of the mold.
While scraping, twist the blade so that it does not scrape straight across the surface of the mold but instead scrapes across it at an angle. This is kind of hard to describe.
The edge of the blade still contacts the surface of the mold all the way across. This will keep the blade of the knife from catching on the straight edged pockets of the mold. I think the video explains it better.
Demolding the blocks. Click on the video on the right to watch it.
This video shows removing the blocks from the mold as well as cleaning the mold and work surfaces.
Let the mold set for at least 20-25 minutes.
Afterward, simply flex
the mold and pop the bricks out. Each brick is perfectly detailed
be extremely accurate in size.
Here is a close-up of a block cast in plaster of Paris. Even though the plaster did not flow into the mold well, using the pound board and surfactant still gave good results.
Let the blocks dry thoroughly before gluing and painting. I got a food dehydrator one Christmas and I wondered "What the heck am I ever going to use this for?" Now it makes a wonderful block dryer which dries them in about 3 hours. Another way to speed up the drying process is to put them in the oven and bake them at a low temperature for a few hours, or place them in front of a fan overnight.
Most any glue can be used to assemble the bricks with. Anything that can glue porous material will work. My favorite is Aleen's Tacky glue that you can get at Wal-Mart or any craft shop.
You can store the molds for up to 2 weeks without any special care. Just stack them flat on top of each other.
If you need to store them for longer than 2 weeks, give them a coat of baby powder (either corn starch or talc) and store them flat in a stack no more than 6 molds high. The baby powder will keep the molds from sticking together.
Keep them out of direct sunlight and away from extreme temperatures. When you use them again, be sure to wash the powder off and your first cast will come out better.
This is the first pound board I had made long ago. You may prefer to use this instead of covering a book with plastic. To make this, you'll need a small piece of plywood, a kitchen sponge and some duct tape. Usually a 1 foot square piece will do.
You can also use a thick piece of Plexiglas or acrylic sheeting instead of plywood which cleans up easier.
Cut the sponge into 4 squares and place one on each corner.
Use the duct tape to hold the sponges in place.
Flip the board over. Now when your pour plaster into the mold, you can pound your fist on the board and it won't shake the whole table. The work surface puts a lot more force into jarring the mold and releasing air bubbles.
If you get plaster on the work surface (and you will), simply scrape it off with the putty knife when it dries.
However, if you really want to do the thing right, you can make a $40 vibrating table to do the pounding for you.
If you're using only one small mold, making a lot of blocks can
take a while. It's best to do this while working on other projects.
I'll pour one mold and
set a timer for 3 minutes.
While I'm waiting, I'll paint a base coat on
a miniature I'm working on.
When the timer goes off, I scrape the mold and
reset the timer for 25 minutes.
While the blocks are setting up,
I'll paint base colors on the miniature until
the timer goes off.
I remove the blocks, pour a new batch and continue the process all over
At the end of the day, I have enough for a building while getting
other projects done.
Another way to increase the amount of blocks you can
make is to simply buy more molds. Many times I have up to 9 different molds
going at once. While three molds are setting up, I'm pouring the next three.
In a couple of hours, I have enough to build a mansion.