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Wednesday: 50F, very cloudy and breezy with heavy showers. I set up during a "blue teaser." Whereupon I discovered the settings for observatory site in Skychart were wrong again. Then it rained hard and I didn't care any more. There were several more cloudbursts running into the evening.
And, running inside the dome! I went over to check how the dome was coping. The worst leak, by far, is half way up the shutters on one side only. This drips straight down onto the floor where it can be easily collected. Probably the horizontal seam which lies over a cross brace. I have arranged a series of square storage tubs on the observatory floor. Their shape means they can be arranged tightly together. Where round buckets would have too many gaps in between. Further sandwich boxes were placed on the base ring to catch the worst of the drips.
It never stopped pouring outside as I searched for leaks with a torch. The smaller leaks are at the vertical, panel seams where they lie over the ribs. I put far too much faith in expensive, flexible, seam fillers. Unfortunately the low angles involved made aluminium, z-shaped, flashing strips pointless. They would just fill with water and sit there to rot the plywood panels over time.
A number of options present themselves. Fibreglass tape and resin on all the joints? That would need cleaning back the paint to the bare plywood. A complete GRP wrap? Expensive with difficult access! Welded rubbed gores? Heavy and I lack the skill to neatly join the vertical overlaps with a flaming torch.
Full height, aluminium gores? I'd need to make, or buy, a sheet metal bender to cope. Though it need only have a capacity of a little over 2' wide. I wonder if there is an affordable Chinese example? I don't really need a proper sheet metal brake. The angles of the facets and their width at the bends are quite modest. They could be achieved with timber. Or timber sections reinforced with right angle metal profiles.
If only I'd had the foresight to have small overlaps on the horizontal joints. At the time I thought, mistakenly, that the sealer would do the job. Besides it wouldn't have been so pretty to have hard lines at all the joints. I thought, at one time, that I might cover the dome in smaller scales. Though I didn't want to use tar based products. Simply because of the weight issue and thermal retention problems.
The angles between panels are too sharp to allow easy overlapping of stiffer materials. The panels tapering from top to bottom would require perfectly scaled "scales" to suit the width of each panel. Rubber pond liner could be glued down to produce a traditional fish scale covering. Though the weight and thermal issues would be a serious drawback. Not sure painting rubber is a good idea. Bare black rubber would be awful for heat build-up.
PVC tarpaulins could be glued or heat welded to form full drop gores. That instantly solves the horizontal seam leakage. Vertical overlaps are easier to achieve with this softer and thinner [waterproof] material but finding suitable colour options might be a problem. Green PVC buildings, like temporary garages, are readily available in a truly hideous, bright grass green. Not sure a sage green is available for an amateur builder's one-off requirement.
My present sage green paint is very pleasant on the eye even as it deteriorates. I have now watched quite a few heat welding tarpaulin videos on YouTube. It looks quite manageable but they have mostly been working indoors. Not dangling by their toes, hooked over a ladder's top rung, while inverted over a dome 20' off the ground, in a howling gale! Perhaps I exaggerate? 😉
A further option exists to have bare tarpaulin stretched over a plywood skeleton. Though I think the plywood panels backing the tarpaulin might be more sensible. Probably offering a longer life by reducing flexure and local wear and tear.
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