stunthanger.com
Building Tips and technical articles. => Paint and finishing => Topic started by: Allan Perret on March 23, 2009, 05:20:46 PM
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At least I think its oxidation. White film that develops when finish is 4~5 months old. I have had this happen using both Brodak and Sig lite-coat. Polishes off easy enough, but I wondering what causes it or what I might do to prevent it. I usually have to spray in humid conditions so I generally use retarder. Could that have anything to do with it ?
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What thinner are you using in your dope?
laquer does age, but 4 months seems rather fast unless its in the sun a lot
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Brodak and Sig, I stayed with the brand's thinner, and retarder. No mixing brands, even though I have posted questions about that. I was just curious.
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"At least I think its oxidation. White film that develops when finish is 4~5 months old. I have had this happen using both Brodak and Sig lite-coat. Polishes off easy enough, but I wondering what causes it or what I might do to prevent it. "
Yes, dope will oxidize.
A coat of auto wax will bring it back to it's shinny past.
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When you sand and polish the surface, you break the "skin" of the dope, opening the pore up. This allows contaminants and oxidizers in. If you keep a coat of wax on it, that limits the intrusion, but ultimately, it will oxidize slightly. As you note, it's pretty easy to bring the shine back. It's worse, in some ways, with catalyzed polyurethanes unless you don't sand them. Once the skin is cut, you open the finish to this sort of thing. Hey, nothings perfect. ;)
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Something else that happens to dope is that it will mildew. The cellulose is attacked the same way old movie film is. This normally happens in a place with fairly high humidity. I have the problem in my basement during the summer months. I get these patches on my models and just buff them off. Randy's also right that wax will at least slow this process.