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John Galloway . uk wrote in message ...
At 16:00 21 December 2003, Jj Sinclair wrote: Oh My, Ruben It sounds like we have finally found someone who actually knows what they are talking about. Your post brings up several questions: for example when you wash your glider, then dry it and finally wax it (because it is all clean now, right?), your drying was never really able to extract the water from the pores. Should we be waxing gelcoat? How about urethane finishes? I have seen little blisters that form when a sailplans is left in a very wet environment, like a metal trailer. When these blisters are popped, a little bit of water is evident under each blister. I have seen this in urethane and also in gelcoat (Prestec) What is your take on this? JJ Sinclair Ruben's post is really interesting and he makes a very strong case for water exerting a damaging shear force between phsically bonded coating layers a refinished glider and for exacerbating cracking - but is it the whole story for gliders with their original finish? I think Bob Lacovara also knows what he is talking about - see his posting of 04-42 on 6th December and also his article (and qualifications) at: http://www.wingsandwheels.com/Weathe...ock%20Tech.htm I will take a lot of convincing not to cover my glider with a UV protectant wax and, preferably, to have a PU finish to reduce the risk of surface crazing from UV degredation. Having suffered badly from water filled blisters on one glider I am very conscious of the effects of moisture but it seems, from what is written about experiences in the boating world, moisture will get in through the composite structure to the gelcoat from the inside out in wet conditions. The boating people say that the water dissolves chemicals out of the resin on its way through and that the water in the blisters tastes chemical but when I tried it on water from our Discus fuselage blisters it was pretty tasteless. The boats are buildt of polyester. The hardener is an acid. In the cured polyester there can be small amounts of acid that react with water. That is why the water coming out of these blisters smells and tastes chemical. Gliders are buildt whit epoxy that does not react with water the same way. Polyestergelcoat is not a very good barrier for water. That is why many boats are painted, under the waterline, with an epoxybased primer. Matts, glider pilot and boatbuilding teacher For crazing I think that UV surface damage top old gelcoat is the main enemy and water can then start to penetrate from the outside. Meantime, in damp conditions, water has been penetrating from inside from new and this can cause blisters even in gliders with less porous coatings So my plan is to get a PU finish, use Wx Seal/Block during really dry spells of weather to keep the external surface as impervious to water and UV as possible and to store the glider in as uv-free dry conditions as I can achieve. John Galloway |
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