An insurance co. called me yesterday and wanted a quote on washing one side of a house with vinyl siding. The house has a direct vent for the furnace and the something went wrong-blowback or whatever. So i went to take a look and tried a test spot. First I used a sodium metasilicate cleaner. Needed something stronger so I used a mildly caustic non-butyl cleaner and did a little better. There's just a liitle soot stain left on the test spot. I scrubbed it with a brush and a little better again. So, on this test spot I'd say I got 90-95 percent of this stuff off. not good enough. I called my pw dealer/chem dealer and he said two step it. He said use an aluminum cleaner then wash with soduim metasilicate and it would work like magic. I've done some searches but came up with nothing definitive so I'm hoping someone could give me a tip or two. The insurance co. doesn't want to pay for this womans house to be sided so they are looking for a quick turn-around (if you can believe that) and actually said they don't have time to look for more estimates from other pw'ers. Any help would be appreciated.