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If a polyester resin or polyester gelcoat fibreglass job goes wrong…
3rd September 2018 TFarrugia

If a polyester resin or polyester gelcoat fibreglass job goes wrong…

Posted in Uncategorised
Blue Gee Boat Repair

Have you allowed enough time before getting worried? If the laminate or coating is thin, and the temperature is low, it may well take the best part of a day to set. If there is high humidity, the surface may well have become contaminated by moisture, and will remain ‘tacky’; check whether the layer is set underneath, by testing with a pin, or something similar.

The first step is to apply some heat (not too much – not over 30 deg. C.) and to be patient – this may do the trick. A common fault is ‘under catalysing’ – it is worth remembering that a polyester resin that has had a ‘whiff’ of catalyst will sooner or later begin to solidify, but it may take a very long time. Be patient, and remember that the first thing to allow the job is time and warmth.

Mixing of neat catalyst onto the surface is not to be recommended – it is imprecise, messy, and may only work for part of the problem. Assuming that the job will not set after allowing time and warmth. Sometimes, over laying the faulty coating with a ‘hot’ mix (adding more than the recommended amount of catalyst to the resin – say no more than 3%) may ‘set off’ the poor coating or laminate – providing the faulty layer is not too thick. Before considering this action, note that the final laminate will be substandard, and that if it does not achieve a satisfactory result, you will have a bigger mess to clear up!Polyester White Gelcoat 1kg

If all else fails, the coating or laminate must be removed. The first approach should be to try scraping the layer off –  it will be very messy – but less than having to try to dilute the resin with acetone, which is a solvent for ‘unset’ polyester resin – this is a last resort. Do not try to burn it off – it will certainly catch fire! It is important to realise that, if the laminate is not going to achieve the desired result, it must be removed. When the area has been stripped of all faulty material, finally clean with acetone, and leave to dry. Check that the underlying surface has not been attacked by the acetone, and is clean and dry before reworking the job. It is equally important to determine why the job failed, reasons may be:

    1. Absence of; or incorrect catalyst addition – be sure!
    1. Bad mixing of catalyst – an indication of this is where some of the job did set, whereas other areas did not.
    1. The job was subjected to freezing/near freezing temperatures (frost can ‘kill’ a polyester mix).
    1. Contamination – deliberate mixing of other solvents/fillers which were contaminated, or incompatible.
    1. Applying over an epoxy surface – ‘free’ epoxy hardener will destroy the ability of polyester catalysts to work.
    1. Moisture in catalyst/resin/fillers/reinforcement.
    1. Use of an epoxy or other system hardener – i.e. not catalyst.
    1. Use of an incompatible catalyst.
    1. Use of wood shavings as filler (if damp or contaminated).
  1. Material substandard, or part of mixed material ‘time expired’.