Fun With Fiberglass
I mentioned Saturday's non-fun with fiberglass. My attempts to sand it smooth were less than successfull--the surface was just too uneven, especially with wads of fiber mat sticking up and out at all angles. Fortunately, I'm only out about $30 for materials--a small price to learn the importance of keeping the temperature warm enough for the resin to flow well.
It turns out that the makers of Sonotube have introduced something called Sonotube Commercial that uses a plastic coating on the paper tube to make it more water resistant, and stronger. I have emailed the manufacturer to find out how much stiffer it is--and if there is a Boise distributor. My thought is that the standard Sonotube is so flexible that even fiberglassing it may not be sufficient. Perhaps starting with Sonotube Commercial (even if it is a bit heavier) might well be worth it. Perhaps it will be rigid enough that it doesn't need anything but a single layer of resin and some paint to meet my needs.
UPDATE: I spoke to the technical sorts at the maker of Sonotube this morning. It turns out that the Sonotube that I grew up with--and that was widely used for making telescopes--is just about gone. What they now make is much thinner, and much flexible. It uses a coating called Rainguard to make it adequate for concrete pouring---but not so much for telescopes. I am not the first call that they have received.
It turns out that the old style Sonotube (which only weighs 3.11 lbs./foot in the 20" diameter) is still made at the Lewiston, Idaho plant, largely because they don't have the paper and adhesives to make the new form. But no one closer than Bozeman, Montana, actually has it. It seems that it may make more sense to use the standard, not terribly stiff form of Sonotube, and fiberglass it--and do it correctly this time, at the right temperature!