I have a specific size and shape in mind: I want a lamp that's 3"x3" and 9" high. I also want a shiny smooth surface right out of the mold, so I don't have to do any sanding.
There are a lot of commercially available resin molds, but I couldn't find anything in this exact size, so I decided to build my own mold.
Uncured resin is wickedly sticky, and it will stick and bond to just about everything. There are a few substances resin won't stick to, so that's where we'll look to find mold materials. This very short list includes:
- HDPE (high-density polyethylene) plastic
- Clear packing tape
- Hot glue
- Melamine (plastic veneered plywood)
I'm using HDPE (high density polyethylene) and hot glue. The HDPE plastic seems to give the smoothest finish, and is fairly inexpensive and easy to work with, and they had it available at my local Tap Plastics, so that's what I used to build my mold.
I cut three pieces to 10" x 4" for the sides and bottom of the mold. I cut two end pieces 3" x 4".
I'm making them an inch larger than the desired size of the finished piece to allow for the thickness of the plastic and give myself plenty of room to add hot glue on the outside of the mold, to hold it all together.
To help with alignment and make things fit tightly, I used my table saw to cut very shallow dado cuts 1/2" from the ends of the side pieces, and on all 4 sides of the bottom piece. This is an optional step but it really helped! The first mold I built did not have the dado cuts and it was really tricky to get all the pieces squared up evenly. I also had a lot more problems with leaks when I didn't use the dado cuts.
Align all the pieces and glue the mold edges together with hot glue on the outside. Use a lot of glue. A LOT of glue. This resin is thin and will seep right out of any cracks it can find.
Once all your edges are glued and secured, fill your mold with water. If there are any drips or leaks, go back and add more glue. I also found it helpful to re-melt my glue with a heat gun and really press the wet glue down into the cracks and corners with a cotton swab.
Repeat your leak-test until your mold is water tight.
Once you've got a water-tight mold, you can use it to measure the exact amount of resin you'll need. Fill your mold with water to the desired depth, and then pour the water out into a graduated container. My mold holds exactly 6 cups of water when I filled it to 3" deep, so that's how much total resin I will mix up.
There are 3 basic categories of epoxy resin: casting resin, tabletop resin, and deep pour epoxy resin. For this project we're using deep pour epoxy. The epoxy I'm using can be poured up to 2" deep. My finished torch will be 3" deep, so that means I'll need to do two separate pours.
I'm using Pourable Plastic resin. This resin is a 2:1 mix type - I'll need twice as much of part A. My earlier water test determined that I need 6 cups of resin total to fill the mold. That works out to 4 cups of part A and 2 cups of part B.
Since I can only pour up to 2" deep, let's cut that in half for our first pour. That means we'll be using 2 cups of A and 1 cup of B this time.
Double Check your Math
If you're using 2:1 epoxy:
Total Measurement / 2 = First Pour Measurement
First Pour Measurement / 3 = Part B Amount
Part B Amount x 2 = Part A Amount
For a 6 cup mold:
6 / 2 = 3 (First Pour Measurement)
3 / 3 = 1 (Part B Amount)
1 x 2 = 2 (Part A Amount)
If you're using 1:1 epoxy it's a bit easier - just divide your total measurement by 4 to get the required amount of each part for the first pour.
We want the color to be exactly the same for both pours. If we just add color willy-nilly to each pour, it'll be very hard to get an exact match.
The torch on the right was my first try. I carefully counted the number of color drops in each pour to get it as close as I could, but as you can see, the two halves don't match very well.
The torch on the left uses the pre-mix color method below, and the seam between pours is much less obvious.
Had I been thinking even further ahead, I could have mixed the color for all four pours so that both torches match each other as well.
To guarantee a color match, we'll add our color to all 4 cups of part A, then mix up half (2 cups) of the colored resin to 1 cup of part B right before each pour.
Add color until your part A is a bit richer and darker than you want the finished torch - remember, it will get diluted a bit when you add the B part.
Mix it up really really well. Unmixed color can leave streaks in your finished torch.
Pour half the colored resin into another container. Cover up the rest and keep it out of the way until you're ready for the second pour.
Add in your part B resin. Mix it up according to the directions - this resin wants to be stirred for five full minutes.
Stir slowly and thoroughly, scraping the sides of the container and occasionally scraping off your mixing stick as well. Unmixed resin can leave sticky or soft spots in your final project.
Also, don't mix too fast! I watched a lot of YouTube videos and saw professionals making resin river tables using a hand-drill based mixer. I tried this at home with disastrous results - the fast-mixed resin got so many bubbles whipped into it that it turned an opaque white and ruined my project. Be patient and mix slowly!
Arrange your fairy light strand artfully inside your mold, with the end of the wire coming out near the bottom. I used a small clamp to hold the wire in place on the bottom of the mold.
Pour the resin in and wait a minute or two, then pop any small bubbles that arise by waving a heat gun above the surface. Don't over-heat the resin. It will do some more out-gassing on its own.
Put your mold someplace that's comfortably within the recommended temperature range on your resin bottle. My room was a bit warm, so I turned a fan on to help keep the temperature down and slow the curing process.
If the resin gets too hot or the pour is too deep, things can get weird.
Wait until your resin is fully cured -- in my case the wait was 48 hours. Mix up the second half of your colored resin with the second half of your part B, and pour it right on top of your first pour. Make sure the lights are fully submerged. Wait another 48 hours. This is taking FOREVER! Be patient.. with luck, it'll all be worth the wait.
Use 99% alcohol to release the hot glue from the mold and pop out your beautiful torch.