How the epoxy calculator works
Resin is sold by volume, so the job is to find the volume of the space you're filling and convert it. Work in inches, multiply out the cubic inches, and divide by 231, the number of cubic inches in a US gallon.
river or rectangle: volume = length × width × depth
round: volume = 3.1416 × (diameter ÷ 2)² × depth
gallons = cubic inches ÷ 231
liters = gallons × 3.785
Here's a typical river table. The river runs the full 72″ length, averages 8″ wide and the slabs are 1 1/2″ thick. That's 72 × 8 × 1.5 = 864 cubic inches. Add 10% and you have 950 cubic inches, or 4.11 gallons (15.6 liters). With a 2:1 product, that's 2.74 gallons of resin and 1.37 of hardener.
If your resin is rated for 1/4″ per pour, that river takes six pours. A deep-pour resin rated for 2″ could do it in one. The plate shows the layers either way, so you can see how many evenings the project will take.
Measure the river, not the slab
Live edges wander. A river that's 5″ at one end and 11″ in the middle isn't an 8″ river until you average it. Lay a tape across the gap every foot or so, add the readings and divide by how many you took. If the live-edge slabs have voids, bark pockets or cracks you plan to fill, add a little for each one.
Measure depth from the bottom of the mold to where you want the finished resin, not to the top of the slab. If you're planning to flatten the whole top afterward, many people pour slightly proud and plane it down. Count that extra in the depth.
Heat, layers and pour depth
Epoxy gets hot as it cures. The thicker the mass, the more heat it holds, and too much heat can crack the resin, cloud it, pull it away from the wood or yellow it. Each product is designed for a maximum thickness per pour, and that number is on the label or the technical data sheet. Use it as the max depth per pour here.
- Coating or tabletop epoxy is made for thin layers: flood coats, seal coats and shallow inlays.
- Deep-pour or casting resin cures slowly so it can go in much thicker, which is what most river tables use.
- Room temperature counts. A warm shop speeds the cure and the heat; a cold one can leave the resin soft. Follow the temperature range on the label.
Between layers, follow the recoat window your product gives. Pour too early and the heat stacks up; wait too long and you may need to sand for the next layer to bond.
Ratios by volume and by weight
A 2:1 ratio by volume isn't 2:1 by weight, because resin and hardener have different densities. If the kit gives both, use whichever you can measure accurately. Graduated cups work for volume; a scale is better for weight on large batches. Mix each pour in one batch when you can, and scrape the sides and bottom of the bucket. Unmixed resin from the walls is the usual cause of soft, sticky spots.
Small steps that save resin
- Seal the wood first with a thin coat brushed into the edges. It stops air in the grain from bubbling up through the pour and cuts down on soak-in.
- Build a tight mold. Melamine or MDF lined with sheathing tape, with every seam caulked. A slow leak overnight can drain a quarter of a pour.
- Keep 10 to 15% extra. Some always stays in the bucket and on the stir stick.
Pricing the wood too? The board foot calculator handles the slabs, and with both numbers you have most of the material cost of the table.