Before we start: All products that have catalyst included, in winter come with winter catalyst. GRP resins require longer curing times in cold weather, as they don’t reach full hardness. Uneven mix can cause weak surfaces, sticky finishes and project delays. Apex Winter Catalyst is designed to help the resin cure in these colder conditions. It ensures GRP roofs, ponds, overlays and other projects are strong and durable. Using the right catalyst avoids mistakes and makes the mixing process easier, produces professional results. Following Apex’s recommended catalyst ratios ensures consistent performance even in the lowest temperatures. How a Catalyst Works Some GRP resins come with a standard catalyst, others are sold as catalyst free systems where the catalyst needs to be added separately. In colder months, standard catalysts react slower. This can cause: Longer curing times Difficulty applying and shaping the resin Risk of not curing fully, reducing strength and durability Apex’s Winter Catalyst is designed to keep your resin curing properly even when it’s around 5-10 °C. So your GRP roof, pond, overlay or other project will work as it should. Every product comes with a mixing chart, which shows the correct grams of catalyst per kilogram of resin. Follow this, and you’ll never have to guess and will get professional results every time. Understanding Catalyst and Resin Ratios Catalyst measurement is key, especially in winter. Too much catalyst can make the resin brittle, too little slows curing or leaves the surface sticky. Each Apex product has a chart for the correct ratios. As a guide: Temperature (°C) Catalyst % by weight Notes 22–35 °C 1% Standard summer ratio 18–22 °C 2% Slightly cool temperatures 12–17 °C 3% Winter applications 0–11 °C 4% Lowest temperatures, winter catalyst required Tip: Always weigh the catalyst. Cold temperatures thicken the resin, and incomplete mixing can cause streaks or uneven curing. Preparing Cold Weather Supplies When you are working in the cold, you have to alter the standard method of application of GRP resin slightly. When you combine and use the resin correctly and monitor the temperature, it will cure with a smooth and strong surface. Below are simple tricks, which can assist professionals and amateurs to achieve good performance during cold weather. Warm Your Materials Before mixing, make sure that your topcoat, catalyst, and resin are at room temperature (18-20 C). This prevents curing unevenly, and it is easier to apply the resin with a uniform thickness. When the weather is cold, it is best to warm the materials slowly to slow down the hardening process and obtain better results. Measure Accurately Take the appropriate volume of catalyst based on the temperature you are operating in using measuring cups or a scale, small error can lead to weak points or sticky surfaces. Precise measurements are easier to mix and yield consistent results. Mix in Small Batches It is important to remember that the resin has a shorter usability period in cold weather. Small batches provide better coverage and control, and conserve material. Watch out Frost or Standing Water Ensure that it is not wet but dry or a little bit moist. The presence of water reduces the bonding power and can lead to cracks in future. adhesive power. When you have the surface ready, you will have a good strong finish, of high quality. Wear Protective Gear Cold resin is sticky and difficult to work with, therefore use gloves and protective clothing. Correct equipment will protect you and will ensure that the resin remains untouched. Applying GRP Resin on Damp or Slightly Wet Surfaces Winter projects often involve surfaces that aren’t completely dry. Apex offers products suitable for these situations: G4 Damp Seal Pond Primer – Bonds effectively to slightly damp surfaces. Certain GRP resins – Compatible with damp or moisture-prone substrates. Application Tips Tips for damp surface applications: Apply primer in thin, even coats to avoid pooling Allow primer to tack-dry before applying resin Use Winter Catalyst to accelerate curing on cold, moist substrates Keep an eye on curing times, as damp conditions can slightly extend them This flexibility helps contractors maintain schedules even in unpredictable winter weather. Recommended Apex Products for Winter Work Apex provides a range of products designed for winter applications: Fibreglass Roofing Resin (Free Catalyst) – Reliable for standard applications, comes with a mixing chart. Winter Catalyst is not included, so it must be added separately for cold-weather use. Heavy Duty Fibreglass Roofing Kit – Complete kit including resin, 600g mat, topcoat, and standard 2% cure catalyst. Suitable for GRP roofs, balconies, and structural projects, and can be applied in cold conditions down to 5 °C. GRP Complete Topcoat Refurb Kits – Perfect for recoating and finishing old GRP roofs. Each kit includes topcoat, standard catalyst, and all tools needed to achieve a smooth, durable surface, scaled to your roof size. G4 Damp Seal Pond Primer – Ideal for slightly damp or cold surfaces, this primer provides a solid base for resin application. Flexi-Tec 2020 GRP Kit – A flexible, winter-ready overlay system with a 10-year guarantee, perfect for balconies, roofs, and areas exposed to cold weather. Using the right kit and the correct catalyst amounts helps you get consistent results, even when conditions are tricky. Advanced Winter Handling Tips for Professionals Professional installers know winter work requires careful planning and execution: Use thermal blankets or temporary coverings to maintain substrate temperature Apply multiple thin coats rather than one thick coat for more even curing Monitor curing times – Even with winter catalyst, colder temperatures will slow reactions slightly Check resin color and tack – Properly catalyzed resin should harden evenly with a smooth finish Maintaining these practices ensures high-quality GRP surfaces, even under cold and damp conditions. Mixing and Application in Cold Temperatures: Step-by-Step Check the temperature of all materials – Resin, catalyst, topcoat, and mat should be kept warm prior to mixing. Measure catalyst precisely – Use scales for accurate measurement according to temperature charts. Mix thoroughly – Cold weather can increase resin viscosity. Stir consistently for even distribution. Apply resin in small sections – Reduces the risk of uneven curing or pooling. Layer the reinforcement mat carefully – Ensure no trapped air, which can delay curing. Monitor curing progress – Touch test or visual check for uniform hardening. Apply topcoat when resin is ready – Prevents overexposure or under-curing. These steps, combined with Apex’s winter catalyst, ensure reliable results. Ordinary Winter Problems and Solutions Resin Sets Too Slowly GRP resin hardens more gradually when cold, and thus it takes longer to cure. This will slow down the work and stick the surface. Solution: Add extra catalyst when working with small batches, and ensure that everything is at room temperature prior to mixing. Surfaces Are Slightly Damp Coating wet or moisture-prone surfaces with resin does not allow it to adhere and cure, leaving weak areas. Remedy: Dry damp areas with a hot air gun, or wipe with acetone to draw out moisture. Use GRP resin or Wet Damp Surface G4 Damp Seal Pond Primer – apply smooth coats, let it dry, then finish with resin for an even surface. Curing Lumps on Large Surfaces The large parts can not heal evenly, some sections hardening more quickly than others and developing bumps or weakness. Remedy: Use several thin layers rather than one thick coating, interlace in applying the coating, and monitor the surface drying. This produces a smooth finish and uniform strength on the surface. Resin Becomes Too Thick The cold resin may solidify and will stick together, making it hard to mix and spread. This may produce streaks or lines. Solution: Heat the resin a bit and then mix it, stir, and add the catalyst in a measured amount. This makes the resin very easy to work with and provides a smooth and strong finish each time. Don't heat the mix after adding the catalyst, your bucket will solidify. Why Professionals Choose Apex Products Apex Fibreglass Roofing Supplies has a reputation for reliable, winter-ready GRP systems: Winter catalyst included with all resins and kits Clear mixing charts for every temperature range Products compatible with damp or cold substrates Comprehensive kits with mat, topcoat, and resin Nationwide delivery and professional support Installers trust Apex because it works reliably, even in winter. Using the right catalyst, mixing correctly, and choosing high-quality products helps projects finish on time without losing strength or a good finish. Planning Winter GRP Projects Winter work requires careful scheduling: Check weather forecasts – Plan for dry periods if possible Pre-warm materials indoors – Avoid starting with cold resin Prepare surfaces in advance – Clean, dry or slightly damp as appropriate Keep tools and work area warm – Helps maintain consistent curing Allocate enough time for curing – Cold conditions extend setting times By planning effectively, installers reduce errors, save time, and maintain quality Maintain Project Quality in Winter Cold weather does not have to slow down GRP projects. Using Apex’s Winter Catalyst-equipped resins ensures: Reliable curing even at low temperatures Compatibility with damp or slightly wet surfaces Precise, professional results following recommended catalyst ratios High-quality finishes suitable for roofs, overlays, and refurbishments Explore Apex’s full range of winter-ready GRP products and kits here.
