Calculate the MEKP catalyst needed for gelcoat from your volume or weight and catalyst percentage, or check the mix rate already added.
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Gelcoat to Catalyst Ratio Formula
The calculator uses one of three formulas depending on the mode you choose.
Volume or weight mode (find catalyst from gelcoat amount):
Check mix mode (find percent from what you already poured):
Ratio form used in the result panel:
- Gelcoat — amount of gelcoat resin, in volume (mL, fl oz, qt, gal) or weight (g, oz, lb).
- Catalyst — MEKP hardener, in the same measurement type as the gelcoat.
- Percent — catalyst amount divided by uncatalyzed gelcoat amount on the specified volume or mass basis, multiplied by 100.
- Ratio — parts gelcoat per 1 part catalyst (for example, 50:1 at 2%).
Volume percentages and weight percentages are different: use the measurement basis specified by the product’s TDS/SDS. The calculator does not convert between those bases because the densities are not supplied. Drop estimates assume 20 drops per mL and vary by dispenser; use calibrated measurement.
Common Mix Rates and Quick Reference
The required MEKP rate and permitted conditions depend on the particular gelcoat and catalyst instructions. The table below shows arithmetic examples on a consistent measurement basis; these are not recommended rates.
| MEKP % | Ratio | Measurement basis |
|---|---|---|
| 1.0% | 100:1 | Same specified basis for both amounts |
| 1.25% | 80:1 | Same specified basis for both amounts |
| 1.5% | ~67:1 | Same specified basis for both amounts |
| 1.75% | ~57:1 | Same specified basis for both amounts |
| 2.0% | 50:1 | Same specified basis for both amounts |
Illustrative catalyst volumes at 1.5% and 2% by volume for US liquid gelcoat measures. Use these only if the product specifies this volume basis; drop counts are approximate:
| Gelcoat | MEKP at 1.5% | MEKP at 2.0% |
|---|---|---|
| 1 fl oz | 0.44 mL (~9 drops) | 0.59 mL (~12 drops) |
| 8 fl oz (1 cup) | 3.55 mL | 4.73 mL |
| 1 qt | 14.2 mL | 18.9 mL |
| 1 gal | 56.8 mL (~1.9 fl oz) | 75.7 mL (~2.6 fl oz) |
Example and FAQ
Example. For an arithmetic example using a product-specified volume rate of 1.8%, you have 1 US quart of uncatalyzed gelcoat. One US quart is 946.35 mL. Catalyst = 946.35 × 0.018 = 17.03 mL. That is about 0.58 fl oz, or roughly 3.5 teaspoons.
What happens if I use too little MEKP? Below the product’s required rate, cure may be slow or incomplete. Follow its instructions; tackiness can also relate to air exposure and wax formulation.
What happens if I use too much? Exceeding the product’s permitted rate can shorten working time and impair the cured material. Check the product’s specified limits rather than applying a universal percentage threshold.
Does temperature matter? Temperature and batch size affect cure and working time. Use the product’s permitted temperature range and catalyst chart; do not adjust the dose from a general rule.
Can I measure by weight? Yes, when the product specifies a weight percentage. Use the Catalyst by weight mode and a calibrated scale. A 2% weight mix is not generally equivalent to a 2% volume mix.
