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Prepare & Paint Airframe Pinholes

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Prepare & Paint Airframe Pinholes

Postby Admin » Wed Feb 11, 2015 1:53 pm

Originally posted by Andy Hollit

PREPARE & PAINT AIRFRAME Pinholes. Hit the entire airframe with a stainless steel wire brush to break through pinholes; (not such a good idea if you want to avoid hours of filling unessessarily revealed pin holes- Vic Leggott) or move along the surface with a hot air gun (unsuported gelcoat will sag). Holding parts against a bright light (1,000W) will also reveal pinholes. Fill pinholes and contours with epoxy bog. A piece of plastic 90mm water pipe makes a good sanding 'block' for in front of the windscreen.
Polyfibre Smooth Prime is an excellent primer (although the hardner has a very limited shelf life). Lightweight, good adhesion and safe to use. Roll it on, then sand it off. Go down to 320/400 using an orbital sander with a vacuum system (borrow the wife's Electrolux!). Round all fibreglass edges, as paint doesn't bond well to a sharp edge. Don't go too fine if using 2 pack as it needs something to 'key' in to, 400 grit is fine, as the paint is quite viscous.

Mask first with 3M Fine Line 218 to prevent paint creeping under, then masking tape on top. Use butchers paper, newspaper is small, has perforations and leaves ink on white surfaces. Remove masking ASAP as hard paint fractures as you peel it off.

Don't use thinners or citrus based cleaners on acrylic windows as they will craze the plastic later. Don't use straight metho on the acrylic as differential cooling may cause cracking. Don't use paper towels or rags containing silicon or the paint won't bond afterwards. Before spraying, remove all marks made by pencil, felt pen, chalk, etc to prevent bleed through. Before spraying, blow out and vacuum fuselage and floor as blast from the gun will blow dust around. Before spraying, damp driveway/floor area to settle dust. Which paint system? My opinion only!! 1. Two pack isocyanate paints give a superb finish, tough and easy to apply; but MUST be used with an air fed respirator (the mask filters available are designed for use in a spray booth where there is a constant flow of air, not the shed!) and suit. I used a cheap High Volume Low Pressure (HVLP) gun and the biggest compressor to run off single phase. Put the compressor where it can't ingest the spray fumes!! You will need a water trap and an oil trap in the respirator line and a water trap in the line for the gun. Isocyanates produce an alergic reaction, rather than a poison/cancer outcome. 2. Automotive acrylic is cheap, easy to apply, safe (in a ventilated area and with the right mask!) and very presentable. 3. Water based 2 packs I tried but couldn't get along with, wanted to run and produced a soft finish, not hard like 2 pack, more like vinyl house paint.

Spraying 2 Pack. Terminology! There's a 'mist coat' (which just dusts the surface) then a 'heavy mist coat'. Next is a 'just wet coat' (where there's enough paint for it to flow out), then there's a 'heavy wet coat' (dangerous because you're on the verge of running). Never paint vertical if you can paint horizontal! Start with edges. First coat mist coat. Wait for it to 'dry' (15 min). This gives the wet coat something to grip, lessening the chance of running. Follow with 3 just wet coats, 15 minutes apart. Use strong lights to view progress.

Leave for 5 days to harden. Resting on a newly painted surface will mar the finish. Rub back with 400, 800, 1200, 1500 wet. Use a rubber sanding block, sand with a crosshatch pattern, not around in circles. Polish with 'Farecla G3' by hand (much better 'feel' than with a buff. Use lots of water.
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