Tutorial for casting with ceramic plaster
Hi everyone… I don’t know if anybody can use this, but nevertheless I wanted to share this with you. It is a tutorial for casting with ceramic plaster which applies for my HQ molds as well as for Bruce Hirsts molds.
To find out more information about HQ-Modular please look here:
or read this thread:
My HQ-Modular board is made out of resin, but after some consideration, I decided NOT to cast floor tiles in resin (english: polyurethane) anymore; first because of the price, and second because of the additional effort that resin requires. I ONLY work with plywood and ceramic plaster. They are faster, cheaper, much easier to cast. Additionally, you can glue ceramic plaster to plywood bases very easily; resin is very difficult to glue.
Here you can find a quick tutorial for casting floor tiles with ceramic plaster. We use ceramic plaster instead of normal plaster because it is much harder and more stable. It is a little more expensive. Normal plaster is also more difficult to cast (stubborn, a lot of air bubbles) and it is very fragile, but allows for good post-production e. g. for walls you can easy break things away with a pair of pliers (ruins). But the floor tiles are supposed to be stable, so we use ceramic plaster.
You will need the following tools:
• ceramic plaster
• 1 special plaster mixing pot
• 1 Japanese spatula
• 1 spoon
Now let’s get started. For one mould with 6 stones, we need approximately 2 spoons of powder.
NOTE: Please keep in mind that this will vary based on spoon size and the concentration of powder you are using. Your first few tries should be tests for you to learn how much powder and water to mix in order to get the optimal results.
Now we add water. It is difficult to describe how much water to add, but it is not very much. We add water with the spoon so we can control how much we put into the pot, but later when you’re more comfortable with the whole process, you can just pour the water directly from the tap.
Stir the powder and water together. If you get the ratio of water to powder correct, the liquid should have a consistency like a milkshake. The plaster should dissolve completely without clumps. The key to having no clumps is to slowly pour the water into the pot; if you pour it in too fast, there tend to be clumps. Use the backside of the spoon to mash any clumps that may have occurred. Once the consistency is like a milkshake, then you have successfully mixed the powder and water.
TIP: If you use warm water, you can speed up how quickly the plaster dries.
Sometimes you have a little more plaster than you need so, in order to not waste material, we always make more than one mould at a time. Make one or two extra tiles if you still have some leftover plaster.
Now we are ready…
…and we can gently fill the moulds. If we pour the plaster too quickly, air bubbles will appear and ruin the plaster, making it unstable and quite unattractive.
As you can see here, we add slightly more plaster into the moulds to make sure they are filled. This is done intentionally so that when the water evaporates, the stone is not too small.
IMPORTANT: After using, you MUST CLEAN your materials IMMEDIATELY. In comparison, dried normal plaster is easy to remove; it just breaks loose. Not the ceramic plaster. You cannot remove it once it has completely settled and your spoon, mixing pot, and spatula will be ruined. And use lots of water when you wash the plaster down the sink—you don’t want dried plaster in your drains and water pipes!
Now take your fists and start pounding on the table, around the mould. With this technique you can release any air bubbles that have possibly accumulated. They will rise to the top because of the vibration. Keep hitting the table until you see the air bubbles rise. Now we take the Japanese spatula and gently scrape it ONCE across the mould, slow but consistent in one stroke. The spatula has to be wider than the mould because the edges would leave ugly marks on the stones. Because of the surface tension, there will still be a little “hill” and that is very important. Because of the density, the water remains ON TOP of the plaster.
Now scrape the spatula ONCE in the other direction over the mould. Between scrapes use WARM water to get rid of residual plaster on the spatula.
Again, pound your fist to get rid of any last few remaining air bubbles. If you have stirred well enough, there should be no bubbles left.
Now it gets tricky; as long as the plaster is not set, you can see the shiny, glossy surface of the water. When the plaster sets (approx. 4–6 minutes), this shine will disappear and the surface looks dull. This happens very quickly, within seconds. Now you make ONE final scrape with your spatula. In that very moment, the surface is beginning to set and feels more like cream or ice, not like liquid anymore. If you wait too long, the consistency feels like butter and the stones are wasted. The surface (the part you later glue to the plywood) is ruined.
Now clean your materials for the next casting.
Now you can relax and wait for the plaster to completely dry. Wait about 20–25 minutes, the time it takes for the ceramic plaster to dry so that you can remove the floor tiles from the mould. Once you have waited long enough, gently bend the mould to remove them.
Even after you remove the floor tiles, there is still excess plaster..
..which can be cleaned with REGULAR WATER ONLY!!! DO NOT use any soap or other cleaning liquids. Just gently rub the mould with your finger.
Now the moulds are ready for the next cast… and the tiles are done
The stones are still very wet inside and have to dry before using. There are different methods to ensure that the plaster is totally set:
1) In the summer, put them on newspaper, and leave them outside under the sun until they are dry.
2) In the winter, put them on newspaper, and leave them near the heater overnight . . . or maybe for two nights.
3) Put them in the oven at approx 100° Celsius (200 °F), but this method does not have a high W.A.F. (Woman Acceptance Factor)
So, I hope you can use any of this information. Thankx to Açoriano3 for cleaning up the mess.