Problem Solver: Polyester Resin

a. Too much hardener.

b. Processing temperature too high.

a. The required amount of hardener varies per type of resin. Carefully check which amount is appropriate for the resin you are using. For laminating resins this is often between 1% and 1.5%, while polyester casting resin may require even less.

b. Process polyester resin at temperatures up to a maximum of 25–30°C. Avoid working in direct sunlight.

a. Too little hardener.

b. Processing temperature too low.

a. Up to a maximum of 3% hardener can be added. Note that our laminating resin has a working time of around 30–40 minutes. Accelerating the curing process has no added benefit within this timeframe.

b. Do not use polyester or vinyl ester resins at temperatures below 12°C. In such cases it is important to use a form of heating to ensure proper curing.

a. Curing too quickly.

b. Curing too slowly.

a. The resin contains additives that migrate to the surface during curing. If polyester resin cures too quickly, these additives cannot reach the surface in time, causing the resin to remain sticky.

b. If curing is too slow, the polyester resin will not cure properly, resulting in a sticky or rubbery finish.

Always remove the tacky layer with acetone before continuing your work.

The laminate has not been properly de-aired.

a. Too little hardener used.

b. Poured too thinly.

a. If insufficient hardener was used, the casting resin may stay sticky. Heat the cast object to 50°C to allow the resin to fully cure. Alternatively, apply a layer of clear spray varnish.

b. Choose the correct amount of hardener for the casting thickness. With varying thicknesses, thinner sections may cure poorly. In that case, heat the object to 50°C or use a clear spray varnish to resolve the issue.

a. Shelf life exceeded.

b. Tin stored too warm or stored at too high a temperature.

a. Polyester resins typically have a shelf life of at least 6 months, and often longer. Vinylester resins have a shelf life of about 3 months, but these can also last longer.

b. Do not store resins in a warm environment and avoid direct sunlight to maintain quality.

a. Cures too quickly.

b. Too much pigment.

c. Curing under a “styrene blanket”.

a. Avoid direct sunlight and work at lower temperatures for best results.

b. Reduce the amount of pigment to improve curing.

c. In bowl-shaped moulds the styrene cannot escape. Place the mould on its side or ensure extraction inside the mould.

The first layer has not cured sufficiently due to:

a. Too little hardener used.

b. Layer applied too thinly or with visible brush marks.

c. Temperature too low.

d. Second layer applied too soon.

a. Ensure you use enough hardener, adjusted to the processing temperature.

b. Apply the correct layer thickness — aim for 300–400 g/m² for optimal curing.

c. Ensure the working environment is warm enough for proper curing.

d. Wait longer before continuing. With sufficient temperature, layer thickness and hardener, wait at least 2 hours.

a. Wrong colour selected.

b. Colour chosen based on a contaminated surface.

a. Determine the correct colour. Use a RAL colour fan in daylight (preferably in the shade) to select the right colour.

b. Check the surface for contamination. Dirt may affect the colour. If in doubt, sand a small area with 1500-grit paper to remove contaminants and assess the colour more accurately.

c. Watch out for colour variations on boats. Colours on the port side, starboard side and transom may fade differently. Determine the colour close to the damaged area for the best match.

Tip: Polyestershoppen can also determine the correct colour based on a sample (at least 2 × 2 cm) and can produce or have the colour produced. Contact our specialists for more information.

a. Shelf life exceeded.

b. Tin stored too warm.

a. Gelcoat and topcoat typically have a shelf life of at least 6 months, and often longer.

b. Avoid storing them in warm environments or in direct sunlight to maintain quality.