A leaking mold can ruin an expensive pour in minutes. A good mold is flat, sealed, level, and easy to release. Here’s how to build one.
Key takeaways
- Melamine-faced board or HDPE sheet make good mold surfaces because epoxy doesn’t stick well to them.
- Seal every seam, and use a release agent or packing tape on surfaces that will touch resin.
- Level the mold and clamp the wood down so it can’t float.
Materials
- Base and sides: melamine-faced particleboard is cheap and smooth. HDPE (high-density polyethylene) sheet costs more but is reusable and releases very easily.
- Sealant: 100% silicone caulk for inside seams.
- Release: a mold release product made for epoxy, or smooth packing tape or sheathing tape on melamine surfaces.
- Screws, clamps and cauls (straight boards) to hold the slabs flat.
Sizing
Make the inside of the mold a little larger than your finished table, about an inch or more on each side, so you can trim the edges cleanly. Make the side walls taller than the finished thickness, plus extra for flattening.
Build steps
- Cut the base and four sides. Screw the sides to the base, pre-drilling to avoid splitting.
- Run a small bead of silicone along every inside seam and smooth it. Let it cure fully.
- Apply tape or mold release to every surface that will touch the epoxy, including the silicone.
- Set the mold on a sturdy, level table. Check with a long level in both directions and shim as needed.
- Place your sealed slabs and clamp them down with cauls across the top. Wood floats in epoxy.
- Test for leaks before your main pour, for example with a small seal pour along the base.
Pour and release
Use a deep-pour epoxy rated for your depth and pour in layers if needed. See how much epoxy for a river table and deep-pour epoxy guide. After the full cure time on the label, remove the screws and tap the sides off. Then flatten, sand and finish: sanding and polishing epoxy.
Header image: Photo: “well-equipped woodworker's workshop” by unknown, CC0 1.0 (cropped).