Gelcoat application and trouble shooting guide
    
Problems or Defects - During Application
  
Problems / Defects - on Moulded Surface
 
 
 
 
 
 
 
   
   
   
   
   
 
Problems or Defects - During Application
Observation
Possible Causes
Remedies
Intermittent Spray
Worn gaskets and seals Replace
Gelcoat starting to gel Flush gun immediately with acetone
Partially blocked jet Strip gun and clean
Low pot pressure Increase pressure to obtain good fan at 50cm distance.
Difficult to spray
Delivery lines too small Increase Diameter of lines.
Gelcoat too cold or too thick Warm to 15°C minimum or dilute with maximum *2% styrene.
Hard gelcoat in gun Soak gun in methylene choride or acetone, then blow it dry.

Poor leveling

Orange Peel
Gelcoat viscosity is too high
Warm Gelcoat to 15°C minimum.
Dilute with maximum *2% styrene.
Atomisation too low Increase pressure to obtain good fan at 50 cm from mould.
Gun held too close Hold Gun 50cm from mould.
Gelcoat temperature too low Warm to 15°C minimum.
Porosity
Poor atomisation.

Pressure too high gives fine porosity.Or Pressure too low gives coarse porosity.

Gelcoat too cold or too thick Warm Gelcoat and mould to minimum 15°C. Thin with maximum *2% Styrene.
Excess or wrong catalyst Maximum 2% catalyst. Check with supplier.
Covering too heavily or too rapidly Lower gun pressure. Hold gun 50cm from mould. Wet thickness .018 - .023 apply in 3 passes.
Water or solvent. Check the product for contamination.
Gun held too close Hold gun 0.6-1.0m from mould surface and as perpendicular as possible.
Uneven Catalysaation Service and calibrate equipment
Wrong or worn tips Replace tips
Catalyst fizz Use correct catalyst
Use of solvents to thin gelcoat Do not thin gelcoat.
Pump cavitation. Check equipment for air leaks.
Sags and Runs
Applied too thick Wet thickness 15-20 thou.
Pressure too high Reduce pressure or move gun 50cm from mould.
Gelcoat too thin. Lower gun pressures, rotate old stock, check with supplier.
Gun too close to mould Keep gun 50cm from mould.
Colour separation
Settling of Colours Stir before use.
Excessive thinning of Gelcoat Don not add more than *2% styrene monomer.
Sagging of Gelcoat Refer to (Sags and Runs).
Overspray. Keep to minimum.
Non-uniform catalysation Mix thoroughly.
Resin Tearing
Gun pressure too high Lower pressure.
Gelcoat too cold or too thick Warm gelcoat and mould to 15°C minimum. Dilute with max *2% styrene.
Gelcoat tip worn Replace tip.
Excessive over spray. Keep to minimum.

Note *:Please note any addition of Styrene will degrade weathering (Chalking, gloss-loss, & yellowing)
of cured gelcoat and increase shrinkage, brittleness, and the risk of pre-release .
Add Styrene only if no other remedy is feasible.
Moulded Surface (Problems, Causes, and Remedies)
Observation
Possible Causes
Remedies
Soft Dull Gelcoat
Wrinkling
Sticking to Mould
Insufficient coverage Apply a total of 18-23 thou. Wet film in 3 passes.
Slow Gel or Cure Increase Catalyst to maximum 2%.
Low temperature Gelcoat and mould must be min. 15°C.
Trapped Styrene Hold Gun at least 50cm away from mould. Adequately ventilate, or tilt mould to expel styrene vapor.
Styrene evaporation Do not use over 30°C.
Uneven Gelcoat Apply at uniform distance from mould.
Wet P.V.A. Release agent Dry thoroughly.
Water/Oil in air lines Flush out and drain traps.
Laminate applied too soon Do not laminate for at least 2 hours.
Uneven Catalysation Service and calibrate equipment
Surge in catalyst delivery Ditto
Pre-Release Refer Pre-Release
Laminate too slow Increase catalyst in laminate if temperature low.

Fibre-Pattern

&

Print Through
Insufficient cure
Correct catalyst level in gelcoat and/or laminate.
Wait longer before pulling. part from mould.
Do not laminate in low temperature.
Check for contamination by water, oil or solvent.
Wait longer before demoulding.
Transferred from mould. Resurface the mould.

Woven roving

Too close to the gel coat.
Should have 3 layers of 1.5 oz. mat or equivalent chop between gelcoat and woven roving.
Gelcoat too thin Use .018 - .023 wet film thickness.
High exotherm of laminate.
Cure laminate slower. Laminate in layers.
Use lower exotherm laminating resin.
Dull part when pulled
Wax build up on mould Polish mould.
Polystyrene build up on mould Scrub with stiff brush or stainless steel wool and strong solvent, rebuff and re-polish.
Dust on mould Keep mould covered when not in use.
Rough or wet P.V.A. Apply smoothly and allow to dry.
Releasing part too soon Allow more time before releasing part from mould, particularly at low temperature
Raw Catalyst Start catalyst flow away from mould.
Pre-Release
Allowing gelcoat to cure too long. Gelcoat must be laminated same day.
Use of waxed gelcoat. Do not use waxed gelcoats on mould.
Excessive or soft wax on mould. Polish mould before use.
Excessive styrene added Add maximum *2% styrene.
Over-catalysation at high temp. Reduce catalyst to 1% minimum.
Uneven cure due to uneven thickness. Apply gelcoat to uniform 18-23 thou.wet film thickness. Avoid heating or fan blowing before gelation.
Uneven cure due to styrene vapor in low spots. Ventilate mould properly.
Gelcoat applied too thick Apply gelcoat at 18-23 thou wet film thickness.
Trapped solvant or water Check for contamination
Moving or Bumping mould Take care untill laminate applied.
Fish Eyes/Pin Holes
Silicone in wax or polishing cloth. Eliminates silicones in contact with mould.
Contaminating on mould. Keep mould covered when not in use.
Excessive thinning of gelcoat. Thin maximum *2% styrene.
Thin gelcoat. Rotate stock, Contact supplier.
Gun pressure too low. Increase pressure to obtain good fan.
Crazing
Too much catalyst in hot weather. Drop catalyst to minimum 1%.
Applied too thick. 18-23 Thou. Wet thickness.
Bad handling when demoulding Demould carefully.
Applied unevenly Keep consistent distance from mould when spraying.
Thinning with acetone or other solvent. Thin only with styrene monomer.
Blisters, Bubbles
Air trapped between gelcoat and laminate. Remove with roller
Over catalysation. Use maximum 2% catalyst
Catalyst Drops Service and calibrate equipment
Poor catalyst dispersion in gelcoat or laminate Mix thoroughly.
Scratched Gelcoat
 Removal of finished article from mould Sand back, buff and polish.
Fading Or Bleaching
Poorly cured gelcoat Refer to remedies “ Soft dull Gelcoat”
Under cure
Allow longer to cure
Ensure correct catalyst
Create air flow to remove access styrene from deep areas.
Water exposure (before full cure) Do not allow water contact untill gelcoat is cured
Inappropriate use of shrink wrap Use only white pollyethylene film.
Exposure to harsh chemicals Clean only with mild detergent solution
Do not use solvents strong alkalies or acidic cleaners
  Refer to supplier.

Spider cracks &
Stress Cracks
Impact damage. Take care hammering moulded parts.
Stress due to flexing.
Take care demoulding parts.
Allow product to cure.
Gelcoat too thick. Use a wet film gauge.
Mould mark Resurface mould.
Laminate too thin. Increase thickness.
Yellowing
Polystyrene / wax build up transferred to part during lay-up. Clean mould regularly.
Poor cure of gelcoat.
Apply gelcoat at correct thickness, catalyst level, and temp.
Avoid contamination by oil, water, or solvent.
Do not add solvents.
Inhibition of cure by styrene vapour.
Thick or uneven gelcoat. Apply at .018 - .023 wet.
Strong Alkaline Cleaners. Avoid cleaners with Ammonia or high pH levels.
Flaking Gelcoat.
Faulty adhesion between gelcoat and lay-up.
Avoid use of soft mould waxes, which can penetrate gelcoat and adversely affect adhesion.
Gelcoat left too long before laminate applied.
Pre-Release Refer to Pre-Release section
Innappropriate use of shrink wrap Use only white polyethylene film.
Contamination Ensure no solvent, moisture, catalyst, dust, or overspray is deposited on gelcoat before laminating.
Pull Marks
Resin Drainage from laminate Avoid resin rich areas
Uneven laminate cure Avoid abrubt changes in laminate thickness
Under cure

Use Correct cat level .

Create airflow over mould to remove styrene from deep areas.
Gelcoat too thick Apply at .023-.025 in 3 passes wet on wet.
Incorrect insertion of cores and stringers Use compressing material between the item and laminate.
Note *:Please note any addition of Styrene will degrade weathering (Chalking, gloss-loss, & yellowing)
of cured gelcoat and increase shrinkage, brittleness, and the risk of pre-release .
Add Styrene only if no other remedy is feasible.
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Synthepol
A Division Of Chemical Specialties Ltd
116 Princes St. Onehunga. P.O.Box, 29109 Greenwoods Cnr, Auckland, New Zealand.
Phone 0064 9 636 8618. Fax 0064 9 636 8618. E Mail synthepol@chemspec.co.nz