Short answer: you can mix epoxy by weight, but only with the weight ratio from the technical data sheet. A 1:1 by volume epoxy is usually not 1:1 by weight because Part A is typically denser than Part B.
Part B per 100 g of A = 100 × (B volume × B density) ÷ (A volume × A density). Densities and the official weight ratio are on the product technical data sheet (TDS); if the TDS lists a weight ratio, use that over any calculation. The default densities above are only an example.
| Product | By volume | By weight |
|---|---|---|
| MAS Table Top Pro | 1:1 | 100:83 |
| WEST SYSTEM 105 + 205/206 | 5:1 | about 100:18 (205) / 100:17.5 (206) |
Manufacturers update formulas, so confirm on the current TDS before relying on any number.
Yes, if you use the manufacturer's weight ratio. Weighing is more accurate for small batches. Using a volume ratio on a scale will usually leave too little hardener.
Usually not. Because resin is denser than hardener, 1:1 by volume often works out closer to 100:80–90 by weight.
Small errors can leave soft or sticky spots; large errors stop the cure. See sticky resin fixes.
On the technical data sheet, as specific gravity or density for each part.
Related: volume↔weight converter · sticky resin fix · resin calculator
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