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Old 05-01-2016, 08:52 PM
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g__day (Matthew)
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Join Date: Dec 2005
Location: Sydney
Posts: 2,564
Well after insistent rains a month or two ago I found I had a persistent leak in one or two spots - most likely from where the steel joins the fibre glass. The seal cracks I suppose if the steel shrinks or expands slightly. Even a minute crack if exposed to water long enough would let some water in - of course to the worse possible spot to leak in the whole lab. So luckly I have a ground sheets over all the electronic PC gear again!

I tried two solutions - a litre at a time I poured about 20 litres of rubber bitumen waterproofing paint through a funnel and S shaped tube under each section of the roof - and what a mess that made above my astrolab PC when it found a leak and then wanted to pour thru for the next 24 hours! Eventually got this sealed but figured it wasn't ideal - as it meant water was leaking in under the steel then pooling until it eventually worked its way down or evaporated.

So my final solution was to properly fibreglass the steel sheets to the dome mounting ring - using about 3" wide strips of fibreglass. This time I used a precision dispenser system that measures the exact correct amount of hardener to resin and apart from strips of the fibreglass fraying easily whilst they were each being resined and then wanting to go everywhere and stick to everything I got the job finished by Sunday - all sanded down - looking great and being really smooth - then I sprayed silicion grease on them to let the waterproof rubber seal on the dome slide easily on them.

After two days of very heavy rain I can finally report it works a complete treat. The steel is firmly bonded to the mounting ring and it is all completely waterproof and the dome turns readily and there is no stiction that I had originally when some of the bitumen paint used in the original seal attempt decided to finally bond to the weatherproof seal! It did pull the weatherproof seal about 10cm out of position - but it hardly matters now that the seal is completely waterproof.

So it all ended very well - and these torrential rains came in very timely to test my handiwork all proved effective.

I think the lessons learnt from this include:

1. Experience is the thing you get after you actually need it
2. Plan ahead but know your plans will go askew somewhere and have to be fixed
3. Once you have done the best you can - make it permanent to really lock things in.

So the final thing I will do after the weather improves is paint the fibre glass marine grade white to protect it against any long term UV effects!

Last edited by g__day; 05-01-2016 at 09:07 PM.
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Old 03-09-2018, 07:05 PM
Finite (John)
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Join Date: Mar 2011
Location: Waikato, NEW ZEALAND
Posts: 90
Well thank goodness for this thread. I have yet to go through the procedure of first building a shed, then making a transition for between it and a 2nd hand 2.3m Sirius dome which will be arriving this week. Old thread but very informative (thanks!)

Have you any photos of the finished roof? I'm very keen to see how it looks, as fibreglass coating of metal sheets forming the transition is what I'd planned to do with mine. Trying to figure out the shape of the transition pieces has been taking up a bit of my time. The only thing I'd like to do differently is to make it with a slight slope down to the edges of the roof.
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