In part two of this tutorial I’m going to talk about casting onlays in your molds. If you missed part one which explains how to make your own molds, you can find it here. There are several different materials that you can use to cast your appliques but the two I like best are plaster and resin. Both are good choices and I don’t think that one is better than the other, it’s really just a matter of personal preference.
Plaster is fairly simple to use. You just mix the powdered plaster with water to the desired consistency and fill your molds, then wait for them to dry. That’s about it. There are no toxic fumes to worry about and you don’t have to wear gloves or goggles. You can wear a mask to protect yourself from accidentally inhaling the powder if you like, although I don’t. I like to make plaster the same consistency as pancake batter because that makes it easier to pour it into the molds and it spreads by itself getting into every little nook and cranny. If your mold has alot of details you can help it along by spreading the plaster with a toothpick or popsicle stick.
I find that plaster takes a long time to dry where I live. It can take a day or more depending on the size of the mold, particularly in humid climates like mine. You must allow it to set completely before you can unmold it because if you try to take it out too soon it can crack and crumble and your piece will be ruined. Test the applique first with your finger while it’s still in the mold. When it feels dry and cool to the touch you can gently begin to pull and unstick the mold from the edges of the applique to remove it. In dryer climates plaster can be ready to unmold in about an hour or so but it will still need a couple more days until it’s completely dry and ready to use. Once it’s fully cured, plaster is surprisingly strong. I’ve dropped plaster appliques on the floor and though of course some do break, others don’t break at all so it isn’t as fragile and brittle as people think. I also like that it’s naturally white so you don’t have to tint it before casting. You can just paint it whatever color you like after it’s been glued on to your furniture. Plaster appliques are particularly nice for adding details to your walls and ceilings as well.
Resin is another great casting material. There are basically three different kinds of resin that I know of. Epoxy resin, polyurethane resin and polyester resin. Epoxy resin is the type most favored by crafters and there are several popular brands sold at crafts and hobby shops. Unlike plaster, resin is quite toxic and it releases toxic fumes particularly while it’s going through the curing process so you do have to take certain safety precautions. But don’t let this scare you off from working with resin. If you are careful, it really isn’t that difficult and it will yield appliques that are strong, resistant, water proof, lightweight and best of all inexpensive. Keep in mind however, that although resin is generally stronger than plaster it is not shatter proof. It can break if you drop it. Before you begin, make sure you have these three things. 1. A facemask 2. Nitrile gloves 3. Safety goggles. I use a thick cotton like mask. I also always work outside. This greatly reduces the possibility of inhaling any fumes because the breeze blows them away. I know that not everyone has 85 degree weather year round or is able to work outdoors, so if you do have to work with resin indoors then make sure all your windows are open and that you have at least one electric tabletop fan that you can angle so that it will blow the fumes out the window. Never work with resin in a closed unventilated space and by all means leave the room while it’s curing. The gloves you will need are nitrile gloves not latex gloves. Disposable nitrile gloves are about as cheap as latex and I get mine at the local pharmacy. Safety glasses are also recommended because you have to mix and stir the resin and you don’t want it accidentally splashing in your eyes.
Resin is a two part mixture, the resin itself and a catalyst. The amount of catalyst will vary according to the type of resin you use. Epoxy resins usually use equal parts of catalyst and resin whereas other types of resin need just a few drops of catalyst. In my area epoxy is almost nonexistent so I use polyester resin which I can find at just about every hardware store and at at car accessories shops. It comes with a small bottle of catalyst because you only need a few drops. The brand that I use calls for 12 drops of catalyst per ounce of resin. That’s really not a whole lot and the bottle of catalyst really lasts. I keep a dropper specifically for this purpose and I use disposable cups to mix it. I recycle plastic cups (we own a convenience store so people leave alot of disposable plastic cups in the waste basket. I salvage them and use them for mixing resin. They can be used several times before they are tossed, just make sure the resin is completely dry before you throw them out. The best way to figure out how much resin you are going to need is to fill your molds with water then empty the water into a plastic cup. Mark the cup at the water level with a permanent marker. This will tell you how much resin you will need for that mold. I like to pre-measure and mark several plastic cups with different amounts so that I can know beforehand how many drops of catalyst to add to each one.
Then I lay out several molds and just begin filling them in order of importance. I fill as many as I can with the amount of resin that I have mixed. Sometimes I mix a larger amount of resin and other times I mix less, depending on how many molds I want to use and on their sizes.
Although they do sell white resin, most resins are naturally clear so your onlays will be clear as well but if you want to tint it before casting your appliques you can do it a couple of different ways.
There are dyes that you can use which are especially made for resins although they can be be expensive. Epoxy resin can also be tinted with regular acrylic craft paint in your color of choice. However, acrylic craft paint will not work with polyester resin. You can tint polyester resin with oil paint, the kind that artists use. I like to tint my appliques white.
Just a drop or two mixed into the resin BEFORE adding the catalyst will yield appliques in any color you want. Make sure you mix the oil paint completely until no streaks remain, then add the catalyst.
Resin is usually quick to set but again it depends on the climate. It usually takes anywhere from 15 to 30 minutes although it can take a bit longer if the weather is cooler or humid.
As the resin is curing it will become very warm, this is normal. If at all possible, let your appliques cure outdoors, make sure they are away from children and pets. Once the appliques are dry you can unmold them by pulling the silicone gently away from the edges. They are ready to use almost immediately and can be painted any color you wish. Once the resin is dry, it is no longer toxic.
Silicone molds should be cleaned after each casting to keep them in tip top shape.
Here is a really good little video that talks about the basics of using Polyester resin.
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