I was asked about my process for creating a plaster mold from a tile. Here it is... Each step is described in the photo captions. Hope some of you find this useful.
Original tile. The blue plastic frame (3d printed) is to keep the tile shape while I make the tile. Useful, but not necessary.
Once tile is finished, I like to pour right away. I have found the wet clay works best in plaster molds (no mold release on the clay is necessary, so it won't obscure the tile detail). The frame is just 4 boards with L brackets at end.
Clamps are added at each L bracket to complete the frame. I measure with a T-square, so the frame is 1.5 inches larger than the tile on each side. This 9 inch square tile has a 12 inch square frame.
Then I add clay along the bottom outside edge to help contain the plaster.
Also run a small bead of clay to the inside, upright seam.
I use Murphy's Wood Soap to all areas (except the clay) that that the plaster will touch. So I coat the wood floor that the tile is on, the inside of the frame and the plastic frame with the wood soap.
It is easy to see the wood soap when applied, so making sure it is all covered is simple.
Next I use my Google spreadsheet to calculate how much plaster and water I need. I just plug in the dimensions of my tile (green boxes) and it figures out how much is needed for me (red boxes). There are several websites that do partial calculations, but I found it was easier to have it all on one page. If anyone wants to use this calculator, here is the link. Please only change the green numbers.
https://docs.google.com/spreadsheets/d/1oMo3YrwjZxIyqBPFwMqhflcbaV2b-Q8eLnoluamCMdg/edit#gid=0
Before you weigh your plaster, put on disposable gloves and wear a mask. Measure your amounts in separate containers you are ready to make your plaster. DO NOT use old plaster (4-6 months max). Use cool water. Warm water speeds up the chemical reaction. The water bucket is always the larger containers as you put the plaster powder in the water. Always add plaster to water.
Slowly add handfuls of plaster to your water. Once all the plaster is in the water. Wait a minute or two while the water saturates the plaster. It will get a wet look (no longer powdery). Once your plaster is mostly saturated, start mixing with your hands (wear disposable gloves) and smush lumps with your fingers. It will start taking on a creamy texture and begin to thicken. This is when I pour into the frame.
Once all the plaster is in the frame. I begin tapping the boards and the plywood with a mallet. This helps any bubbles float up and away from the tile to ensure an accurate model. I keep tapping until I stop seeing bubbles. 🫧
Don't worry if a little plaster seeps out. Almost always happens. While the plaster is setting, this is when I wash my bucket, while the plaster is still in liquid form. I use a hose outside. NEVER wash in your house or studio sink. The plaster will clog your pipes!
Leave for about an hour. The plaster will heat up, then cool. Once cool, you can pull off the frame. Be careful, the plaster is still soft.
When you pull the tile out of the plaster, care must be taken to not gouge the plaster.
At this point I use a rasp to soften the outside edges of the mold (plaster can be quite sharp). I also look for undercut edges in the tile on the plaster mold. If I see any, they are easy to fix while the plaster is still soft, by just scraping my finger nail over it. Let the plaster mold set for about a week before using, so it is at full strength and no longer saturated. You will know when it is ready, the mold surface will feel almost powdery. Don’t use yet if it still feels sweaty. Before first use wipe with a damp sponge to clean the surface where the clay touched.
Here is the link for all who want it. Didn't realize so many would be interested.
Please only change the green numbers. Thanks! The red numbers at the bottom are your measurements.
https://docs.google.com/spreadsheets/d/1oMo3YrwjZxIyqBPFwMqhflcbaV2b-Q8eLnoluamCMdg/edit?usp=drivesdk
Please message me if you have any questions about this process. Thanks for your interest. 🙂