Advice requested. Best way to waterproof a flat roof with a Sirius Astrodome mounted

[g__day]

I have recently changed my hand made astro dome for a Sirius labs 2.3 metre astro dome. It sits on a 2.5 metre astrolab that due to my lack of foresight has a flat roof which works brilliantly as a shallow water basin!

So of course it has a small leak which in accordance with Murphy's law sits directly over all my PC and monitors (which thankfully were wrapped away in plastic) :)

The Sirius Observatories dome sits on a 10cm high, 2.3 metre diameter mounting ring. This mounting ring sits on a circular wooden frame in the roof of the square astrolab. I wrapped the join with the roof in 10cm wide, 1cm thick foam tape running tree times all around the join and taped solidly in (not shown in pictures below) . The roof is 5 mm fibrous cement sheet roof nailed to the wooden frame. The fibrous cement is covered with clear polycarbonate and siliconed in, and bitumen painted and again covered in plastic ground sheet... and the sucker still leaks in exactly the wrong place!

So I would like to build a waterproof membrane from say 8cm up the 10cm high dome Mounting ring and shape it so it slope down to the edge of the square astrolab. The edges of the square astrolab lie between 8cm (at the mid point of each side of the square) to 25 cm at the furthest (along) the diagonal on the corners of the square astrolab.

Can folks suggest the best way / material to economically and sensibly waterproof this sucker to ensure rain water flows off the roof?

I could potentially do any of:


Buy a ground sheet - cut a 2.3 metre diameter hole in it - throw it over the dome and tape it to the edges of the square astro lab (very, cheap, dirty and probably only a temporary fix)
Pack from the mounting ring to the edges of the square with foam, cardboard or plaster, shape it slopes so water runs off and waterproof this somehow
Shape it as per the above then fibreglass it (but I am pretty bad when it comes to fibre glassing)

Appreciate any suggestions folks can give me! Pictures of the problem child follow :)

[cstocky]

Hi Matthew,

My old observatory was a 2.7m diameter dome on round ring (timber with steel support) mounted on top of a 3.0m x 2.4m section supported by steel box section and clad in Colorbond flat sheeting. I initially had enormous trouble with sealing the two sections together. It leaked in the same spot as yours - over the keyboard & electronics. I tried Silastic which would work for a few weeks, however it would always harden and shrink - even the outdoor compatible varieties. What eventually worked and stayed weather proof for nearly 17 years (until I sold it and upgraded to a Sirius 3.5m) was "Concrete Foam Expansion Joint" material used as a gigantic gasket between the mating surfaces. To add some protection I sealed the outside exposed compressed gap with Sikaflex. This is more expensive than Silastic however it lasts 10 times longer and remains significantly more flexible :thumbsup:. I painted over the Sikaflex with Wattyl Solaguard to provide final sun protection (same colour as the Colorbond).

Hope this helps.
Cheers,
Chris

[ZeroID]

I assume the water is coming in somewhere under the round dome ring. Are you not able to define the ingress point ?
I have done some marine work in the past and we used a stuff called Everdure for sealing\hardening wood. It is a 2 pot mixture which we would at first dilute with turps 3:1 Turps\Everdure so it was very dilute. Paint it on over the affected area and let it soak in and harden, then next coat at 1:1 Turps\Everdure, final coat is straight Everdure. When diluted it would penetrate solid wood or fine cracks then harden and seal permanently. You could paint it on rotten timber and after the third application it was like concrete and could be drilled and tapped. Essentially a low viscosity epoxy that could penetrate like CRC. It would find any crack or even quite solid material and turn it into rock.

Another idea. If you can't seal under the dome ring how about adding an 'apron' to the bottom of the dome that overhangs the roof by a wee bit when parked ?
You seem to have clearance for it to be 'misaligned' when the dome has been rotated and at 25cm it isn't too big to be self supporting. Sealed against the dome with a good sealant as suggested above. Sort of a more permanent derivative of your cheap and nasty ground sheet idea.

[Auster1b]

Hey Mathew,

Obviously it needs to be permanent, so I would suggest making a transition out of galvanised sheet, attaching to the ring and obs roof.

Cutout 4 of these:

Bend on the light blue lines to match the ring, bend on the dark blue lines to make a flange to match the obs, join the tabs;
Silastic to your hearts content to seal.

Search storv (square to round freeware sheetmetal calculator).
I just used 2300 for the ring, 2300 square for the obs, 75 high and added some flanges.

Make a trial out of cardboard first to get the hang of it.

Neil.

[Shiraz]

Consider covering any possible ingress points with this sort of stuff - it isn't really cheap, but it works instantly https://www.masters.com.au/product/900006755/fastfix-aluminium-reinforced-butyl-flashing-tape-150mmx5m.jsp;jsessionid=Gii1u-twBRZdCIzFhQMzXQ__.ncdlmorasp1204?b mUID=kT1eYVp. If you make a skirt join between the roof and the dome, it will be flexible enough to deal with any movement and it will certainly keep the water out.

I used similar stuff on a skylight in my daughter's apartment on key Biscayne and it withstood Hurricane Sandy. Bought some at Bunnings in Adelaide a couple of months ago, but most hardware stores will have something similar - although I have the impression that the butyl based ones have better adhesive characteristics than the pitch based ones. The butyl adheres like nothing else, but I also give it a gentle tap with a rubber mallet to make sure it has no airgaps at all.

[g__day]

Well I packed the leaking corner with extra foam, then poly carbonate and then more ground sheet and taped this in position with bear tape. So one out of three corners is shaped correct and is probably watertight for the moment.

I like all the suggestions above so am still considering. The local hardware store strongly advised shaping it any way I like and then fibre glassing it - as most substances will break down outdoors because of the UV - in there words only fibre glass offer long term protection.

[glend]

Hardware store people generally don't know too much but like to refer to what they have. Fibreglass resins will breakdown if exposed to uv light over time, and this includes epoxy resins - you must coat it with a protective barrier paint; they are also very messy to use as a sealant in the sort of situation you have; additionally fibreglass does not bond well to any sort of plastic (like your polycarbonate) to get abond to the dome you might need to 'key' it by grinding back to the glass surface (assuming its a fibreglass dome - if plastic forget it). Personally I would not put on anything that cannot be removed if necessary. There are many long lasting butyl tape solutions available used to repair caravan rroof leaks that would work well and be far less mess that fibreglass. I used a wide butyl tape (white in colour) to waterproof a hinge seal on my camper and it works great.

Have a look at StickNBond products:

http://www.sticknbond.com/

That is the stuff I brought in for my camper sealing job - mainly because I wanted a white tape that would match the camper roof and last under our UV for many years.

[g__day]

Now the hardware store recommends do the framing as suggest - but cover it in Colourbond rather than marine ply and don't bother to fibreglass it!

[g__day]

Convincing the hardware store SRSC that you can indeed cut 1.3m * 1.36m triangles for the corners from a steel roll that is only 1.2 metres wide. Finally a real world use for all that trigonometry we learnt at school!

Took me ages to realise that the Sirius Dome ring for the 2.3 metre dome is 2.34 metre diameter - then it all worked out!

[gts055]

Hii Matthew, I wonder if you could take some images of the triangles before fitting to the roof/dome and then some images during and after installation to show how it fits and is finished. I have the same dome on a cylindrical wood framed wall, that I clad in Bluescope mini orb colorbond. I don't have any leaks yet but would like to finish the flat surface between the wall and dome ring with something similar to what you have decided on. thx Mark

[g__day]

Will do Mark.

One thing I should have done a lot earlier. When cutting the slats cut the corner ones first - then run a string line around each - as you want to cut to a height to give a consistent end height IMHO.

My slats overhang past the roof line by 5 cm. Each starts from 9cm up the 10cm high dome mounting ring. The longest struts have a length of 62cm and an end height of 3.5cm - so the shortest struts at the end point will probably be only 25 - 30mm at the end.

Pictures to follow.

[g__day]

Well the fabricators delivered the corners, but they accidentally cut them off the old plan, with the wrong measurements (front desk gave them a two versions old plan - not the final one).

So they are collecting the pieces and hopefully getting back to me with the correct sizes second time around!

[gts055]

Looks excellent. Just wondering how much increase in friction there will be with the domes's rubber weather seal resting on the new sheet metal. Mark

[g__day]

If they cut them right - very minimal, as its meant to sit a few millimeters under the top of the mounting ring and just be silicioned up at the seal!

[g__day]

Well its all done, bar a bit of painting of the wooden struts (that are weatherproof anyway). Got it all attached and siliconed up about two minutes before the heavens opened - so that was very pleasing! Eight hours later I can report its beautifully watertight now!

[g__day]

Well one small challenge I have to address; the silicon sealant sticks to the rubber skirt of the dome slightly when its sits for a couple of hours. When I initially did the sealing I used plastic clothes pegs to lift the rubber skirt off the silicon and let it set for several hours. I guess the silicon hasn't 100% dried any or some got stuck to the rubber waterproofing skirt at the base of the dome.

I peeled of any excess silicon with a knife, then rubbed all around the skirt with Mineral Turps to remove any residual problem - but the slight stick is still there.

So what do folk recommend, do I:



Wait some more for the Silicon to cure further?
Clean the skirt again?
Shave more silicon from the join?
Coat the silicon on the join with Lithium grease so the rubber skirt isn't actually ever touching the silicon?


Many thanks for your ideas folks!

[gts055]

Hmmm thats a bit disappointing. Maybe try to cut away excess silicone and try "rubber grease" (used when installing rubber seals in brake components such as calipers and master cylinders). Comes in a tube like toothpaste and available at auto parts suppliers. Mark

[g__day]

Thanks Mark,

Its only a discrete moment of grip when you first try and move the dome for the first few centimeters - then all is well until it sits still for a while.

Local hardware store offered the only real solution is to slightly re-coat the silicon again - with a very thin layer - and whilst it is still wet spray it with WD40. They are sure this will work, provided the silicon is still wet when it is sprayed. Does this sound right to folks - and can anyone explain why this works?

[g__day]

Well I walked up to the local store to buy a can of WD40 and have a chat - and did they have a great old school trick to fix things once and for all. Basically they said the Silicon I used was a polymer - so it will never completely dry and hence it will always stick a bit. Any grease or spray I put on would need continual re-coating and would trap dirt and grime - cause nothing sticks to silicon...

Except bee's wax! They said get some good old fashioned bee's wax and pour it ever so thinly around the Silicon and it will grip and seal it and the rubber won't bind to the Silicon or the wax. What makes it even sweeter is my wife's hobby - making bee's wax candles :)

It all works unexpectedly well. One tiny candle later and its good bye grip! Can't believe how high tech and old school bee's wax sorted things - I am stoked!

PS

Tested it again this morning - works beautifully!

[gts055]

Beeutiful idea, Mark :)

[g__day]

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!

[Finite]

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.