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The process of preparing the plane is absolutely crucial to a successful finished product. Surface PreparationFirst, always start with carefully and thoroughly cleaning the surface of your plane. The components of your plane are coated with mold release, which is usually a silicon/wax combination, which is a real problem for adhesion with all the products we will be putting on the surfaces. I suggest that you use MEK RM 901 or 902. This is the only product I have found that works without fail. Wet the surface liberally, then wipe with a clean paper towel. The paper towel absorbs the oils and waxes that have been freed up by the solvents. I have witnessed adhesion problems due to poor surface preparation on some planes I've been involved with. In most cases you're not that lucky -- the problem comes out a year or so down the road and the repair can be a real nightmare. Take the time to clean surfaces with MEK, wax and grease remover, or whatever you use before each application of any substrate. A little time spent now, can save you hours of work later on. Scuff SurfaceNext scuff up the complete surface with 80-grit sandpaper. This will give the surface the friction needed to adhere. Most paint failures are not a result of the products used, but bad surface preparation. FillingFilling a low spot or building up the area around a high spot are probably the most frequent tasks when preparing a plane. First we need to figure out if we have a low spot or a high spot. One way I found helps is to run your hand over the area in question from the tip of your finger to the palm of your hand, not in a waving motion from thumb to little finger. You'll get more area of your hand to feel and millions more nerves feeling for you. I think you'll find this is a much easier and accurate way of feeling the contour of the surface. If you feel as though there are two bumps or two areas, this generally is a low spot. You're feeling first going into the hole and then going out of the hole. A high spot generally feels only one bump as your hand goes over the top of it. I suggest that all repairs that will require 3/16" or more filling be done with micro and epoxy, not polyester filler. Polyester filler will shrink and give no strength to the surface and in fact will be the weakest component in the project. These areas include fillets around the wing roots and tail stabilizer, etc. Areas where you will be filling to get a level fit such as gear doors, canopy to fuselage header, tank to engine cowl, etc., will also need micro because of the depth of the fill. Micro is stronger and will not shrink like auto body filler will and it is 1/3 the weight. Try and get all repairs to at least 1/8" or less and then use polyester skim coat or urethane primer surfacer to feather it the rest of the way. I have written about the pros and cons of using Jeffco or any other brand of fast-setting epoxy to mix with micro for the purpose of filling in Lancair Network News. At that time I came out against it--just using common sense! If it were used to fill around leading edges or areas of potential high impact, such as the canopy closure area, I felt it would fail. I have now witnessed the result of using this technique. I saw a professionally built Glass Air that was flown through some light rain at about 210 knots. The plane looks like it was hit by shotgun pellets. The impact broke through the paint and then an air-over-hydro effect caused deep penetrations into the soft filler. This is a complete nightmare to fix. I hope that everyone who has used this technique in impact areas will think hard about redoing it with the slower lay-up resin. It hardens slower and wets out the micro better which is why it is denser and harder. It’s okay to use it on the tops of wings, etc., but not in frontal areas. |
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