Mixing Polyester Resin in Namibian Heat: A Catalyst Ratio Guide
Polyester resin cures by an exothermic reaction whose speed roughly doubles with every 10°C — which means a workshop in Walvis Bay's winter fog and the same workshop in a January heatwave are two different chemistry sets. The catalyst ratio must move with the thermometer.
The working rules
- Hot (30°C+): drop toward 1% MEKP, mix small batches, shade the resin drums, and work early. A 2% mix at 38°C gels while you wet out the second layer.
- Mild (20–28°C): the data-sheet 1.5–2% behaves as printed.
- Cold (below 18°C — coastal fog mornings): full 2%, warm the workspace if you can, and consider accelerator — but never mix accelerator and MEKP directly together. Accelerator into resin first, always; the direct reaction is violent.
Exotherm is a fire risk, not just a waste
A catalysed bucket generates its own heat: leftover mix concentrated in a container can smoke and ignite. Spread waste resin thin on cardboard to cure. In our summers this goes from advice to rule.
Log your shop's own table
The professional habit: note ratio, temperature and gel time on every job for a season. Your shed, your resin batch, your table — better than any printed chart, including this one.
We stock Butanox M50, MEKP NA 2 and accelerator alongside the NCS resin range at both branches, with seasonal starting ratios from the counter. Quote your whole lay-up in one order.