Master the Art of Epoxy Casting - Part 1: Preparation

Have you ever admired those massive hand-made epoxy river tables? Or maybe smaller epoxy items, like serving trays, knife holders, or lamps?

I've been sold on carpentry and epoxy since that first YouTube video I watched years ago. The epoxy casting process needs preparation and know-how. However, the results are beautiful and worth it. Let's go through the process together and learn some valuable tricks that make it as easy as possible.

Contents Part 1 - Preparation

1. How big is your project?

2. How much epoxy will you need?

3. Epoxy selection

4. Casting preparation

5. Making casts and molds

6. Mixing

7. Casting

Contents Part 2 - Processing

1. Rough mold processing

2. Cut to size

3. Sanding

4. Repairs

5. Surface finish

Contents Part 3 - Lessons learned

1. Mixing

2. Bubbles

3. Leaks

4. Bending

5. Shelf life

6. Tools

1. How big is your project?

Plan and prepare in advance. I strongly suggest you begin with something small like serving trays or inlays.

2. How much epoxy resin will you need?

Epoxy is typically sold in kilos or pounds. You need to (roughly) calculate the volume you will use (in liters or gallons) and use the figure to calculate the weight of the epoxy you need.
Most epoxy manufacturers provide direct volume-weight calculators reflecting the density of their products.

Cured epoxy shrinks a little (2-5%), so plan with that in mind before beginning. A good rule of thumb is to order at least 10% more than you think you need.

• Check out this Epodex calculator:
  https://www.epodex.com/en/media/epoxy-resin-calculator/

• Click the link below for an excellent brand-neutral volume calculator:
  https://www.omnicalculator.com/construction/epoxy

3. Epoxy selection

The fundamental properties to consider are the following:

• Maximum cast thickness

• Maximum mix volume

• Processing time

• Hardening time

Generally, the lower the maximum casting thickness, the less hardening time is needed. For example, 1-2cm of casting thickness means 24-hour hardening time, while a 5-10cm epoxy layer takes up to 72 hours to harden.

What happens if you do not respect the casting/thickness ratio?

• The exothermic reaction starts within a few minutes, leading to a chemical reaction causing a rapid temperature increase that boils the entire mixture 🥵

• The project is destroyed ☠️

I recommend trying out several brands. The cheaper ones are uncomfortable to work with because of the hideous chemical smell and inconvenient measures.

Choose the epoxy product adequate for your project. Personally, I keep the thick and thin layer variants in my workshop.

• A thin layer of epoxy (up to 1cm with 24-hour hardening) is best for small projects, inlays, and surface sealing (don't wait too long between layers)

• A thick layer of epoxy (up to 5cm and 72hr hardening) is better for bigger pieces.

4. Casting preparation

Liquid epoxy has a very low viscosity. Keeping it in your intended casting area is challenging because even the most minor imperfection in the cast leads to leaks. In the worst-case scenario, when you enter your workshop the day after casting, most of the epoxy has hardened on the floor 🤬

The following preparation tips are helpful:

• Find an appropriate space with adequate ventilation.
  Even if the final product is certified as safe even for food contact, the chemical reaction of epoxy during the hardening process releases dangerous, volatile compounds. You definitely don't want that in your living room.

• Ensure you set up your workbench to be FLAT. I recommend using a spirit level.

Cover your workbench with plastic wrap or tin foil.
Be prepared for potential mixture leaks. Maybe it won't happen on your first project, but it will happen. Epoxy does not sick to Polyethylene (PE); remember that well. 😉 

5. Making casts and molds

You can make your casts and molds from multiple materials, such as:

• Soft silicon molds are useful for casting smaller objects, and you can use them multiple times

  

  source: totalboats.com

• Polyethylene (PE) molds are typically pre-made from PE or HDPE. They are helpful for larger projects and are reusable.

  

  source: amazon.com

• Melamine and plywood are the most common molds for home crafts. You can make them in whatever size you need. Remember to seal the joints and corners with silicon. If you use melamine as your base material, treat it with an epoxy separator before casting.
  If you use plywood, you must cover the surfaces that will be in contact with the epoxy with polyethylene (plastic wrap or aluminum foil (kitchen foil). If you need to use various strips, ensure they overlap each other.

  

  source: instructables.com

Please remember that the mold must always be deeper than the product you are making.

6. Mixing

Epoxy resin consists of 2 components

• Component A: Resin

• Component B: Hardener

You buy them separately and mix them just before use in the exact ratio recommended by the manufacturer. For example, 2 x A to 1 x B.

• Prepare a mixing cup. Consider the volume you need and do not overfill the cup; leave at least ¼ cup empty 💦. That will make stirring much easier. If necessary, you can mix in batches and add layers. It's more work but delivers better results.
  

  

• Prepare weighing scales. For smaller projects, use a precise digital scale. Remember that the scale must be capable of measuring at least one full cup.

• I prefer weighing component B in the cup first. I believe it makes the mix more uniform.

• Write down the actual volume of component B to accurately calculate the amount of component A to add.

• Reset the scale and add the amount of component A you have calculated.

• Feel free to add colored powder or ink tints as needed.

• Stir the mixture slowly and carefully with a stick or spatula for one minute. Try to eliminate as many air bubbles as possible. Ensure you mix any components on the side or bottom of your cup. The whole mixture must be homogenous when you have finished.  

• When you have finished mixing, leave the cup to rest for 10-15 minutes to release air bubbles in the mixture. If you have the opportunity, use a vacuum chamber. They are very effective in separating the bubbles and make a HUGE difference, especially with transparent castings.

7. Casting

Please ensure the wooden components of your cast are well fixed (you don't want them moved when the epoxy has set).

Slowly pour the prepared mixture into the mold, avoiding additional air bubbles.

Wait for the epoxy to level and release all air bubbles. Very carefully remove any remaining air bubbles from the surface with a heat gun or blowtorch. Personally, I prefer a heat gun because they are safer. Be careful not to focus the heat on any area for too long, which can cause the epoxy to overheat and discolor. Repeat as needed.

Covering the form during hardening is a good idea to stop dust, insects, and other unwelcome particles ruining your project.

The chemical reaction will increase the viscosity within a few hours. Do not remove your form from the mold until the epoxy has fully cured. Respect the hardening time.

Congratulations on your first epoxy cast 🥳

How do you turn your epoxy cast into a refined product?

…to be continued in Part 2