Peeling paint on plywood dome.

[Skipper Billy]

On bare wood a coat of International Pre-Kote - its has amazing covering power and acts as a primer/undercoat.

On sound existing paint just sand to give a key and degrease.

On joints as long as there is no movement then nothing special required. If filling is required use a polyurethane mastic such as Zycore or Sikaflex 291

If there is any joint movement then it should be taped and the tape coated with polyester or epoxy resin before painting.

[saac]

7 hours ago, Skipper Billy said:

I have used it extensively on wooden boats which flex a LOT and are dipped in and out of sea water - freezing cold then baked in sun - it is very tough stuff.

I painted the south facing wall of our wooden garage with it 11 years ago and it is still perfect. Avoid red if it gets a lot of UK.

Thanks Billy, I'll give it a try, fed up being disappointed by the Deluxe paint and Im ever mindful now of doing work up on the roof - I need something that will last. 

Jim

[Rusted]

Going back to the GRP option:

How many layers and of what? CSM + polyester resin?

Finish off with a coloured gel coat?

[Kev M]

There are Acrylic resins out there that may be an easier option.

" Cromapol Acrylic Waterproofing Coating " is an example ( other makes exist).

They are basically Resin with built in fibres.... they have good reviews.

Just paint it on.

 

 

[Skipper Billy]

If you go the resin route I wouldnt use CSM I would glass fibre tissue - doesnt disintegrate like CSM - esier to work with and requires a lot less resin to fill it and is therefore easier, cheaper and a lot lighter. If you use epoxy resin it will still need painting as epoxy has very poor UV resistance.

[Astro-Geek]

2 hours ago, Rusted said:

Going back to the GRP option:

How many layers and of what? CSM + polyester resin?

Finish off with a coloured gel coat?

On my flat garage roof  (as pictured in my post above), I used two layers of mat and polyester resin and then pigment gelcoat.

Now that DIY kits for flat roofs have become popular, the costs of the fairly large quantity of resin and mat have become very competitive via mail order.

I used these people  https://www.fibreglassroofingsupplies.co.uk/category/grp-roofing-packs       (I can't claim it to be a "Which" best buy recommendation, as I've only used that one company, and only once, but the service was prompt and the materials were excellent.)

The kit I used for my 3 metre wide 6 metre long flat roof was:

Roofing Pack - 1 x 600g + Topcoat (Premium Roofing Resin) Light Grey-20 Sq Mtr    £222.50 plus vat  (then)

It included a hefty roll of mat and 40 litres of layup resin plus 15 litres of gelcoat ("topcoat"),  so being able to buy it as a mass produced kit was so much cheaper than sourcing that quantity of materials elsewhere.

As your dome naturally sheds snow and rainwater, I would think you could get away with just one layer of mat (the 600g CSM is quite thick).

I also bought from them the preformed plastic edge sections that were GRP matted over to form the raised edges neatly, and I had already covered the roof with OSB sterling board T&G exterior chipboard, (as they recommended), but you won't need to do either of those with your dome.

The skin this formed is amazingly impervious to weathering, and as it's really stuck to the surface, it has strengthened it as well. (as it would your segmented plywood dome, makeing it effectively one piece.)

 

Edited June 6, 2020 by Astro-Geek

[Guest]

I think the biggest problem with plywood, is that the layers delaminate once wet. I think the glue is perhaps water soluble, therefore the board's integrity starts to fail. 🤔

Edited June 6, 2020 by Guest

[Astro-Geek]

48 minutes ago, merlin100 said:

I think the biggest problem with plywood, is that the layers delaminate once wet. I think the glue is perhaps water soluble, therefore the board's integrity starts to fail. 🤔

...maybe that's another plus for the fibreglassing method.

In effect, the original dome is just being used as a mould, so the fibreglass skin is a complete new entity in itself, not depending on the thin plywood panels for strength any more.  Though the internal ribs are still essential to provide rigidity.

[Rusted]

Thanks for all your very thorough and useful replies.

It rained hard while I was tidying up my imaging kit to go back indoors.
So it was literally dripping inside the dome as I hurriedly packed my carrying case for the dash to the house.
My precious, plywood, DIY dome suddenly felt horribly weak and vulnerable!

So now I am seriously considering a Pulsar 2.7m dome replacement.
No more "high altitude" ongoing, maintenance problems on dangerous, ladder, lash ups.
I'm close to my mid 70s and getting no younger.

I'd quite probably gain a huge improvement thermally for my solar imaging.
The narrower, up and over shutter could be half opened to reduce wind loading on the scopes.
That would also shield me from the high summer sun.
Far better than my present over the zenith, bi-parting shutters!

My huge, DIY GEM already has serious offset issues with my long refractors.
If I do downsize the dome I'd lose about a foot on inside diameter at [inside] base ring height.

So I'd build a specialist short, equatorial fork mounted on the existing, massive polar axis and pier.
I don't need whole sky coverage for the sun and only occasional lunar imaging.

A Pulsar dome would need a waterproof apron to sit on and to throw rainwater outside the existing octagonal building.
That could easily be built off the top of the existing base ring. 
The existing, octagonal building would continue largely unchanged except for the new plastic "lid."

[Davey-T]

Did you see @Bukko thread on domes, from Poland I think, don't know how size / cost compare to Pulsar but they look very well made.

Dave

 

Edited June 6, 2020 by Davey-T

[Rusted]

Yes. Thanks Dave.

From diminished memory I thought they were far more expensive than Pulsar.
Weren't they floor level rotation rings too?

[Davey-T]

Look better built than Pulsar and suit your setup.

Dave

[Rusted]

Thanks Dave.

The sophistication of the Scopedome does seem to match its higher asking price.
Almost double that of the Pulsar short wall.

The Scope-dome's low rotation ring and low threshold better suits Newts.
My long refractors are well above head height when parked E-W.

I can't even see out of the slit without a step-up.
The relative lightness, size and simplicity of the Pulsar short wall suits a one-man build 14' off the ground.
I seriously doubt anybody sensible would quote for installation on my raised level without danger money.

Are you suggesting, in roundabout sort of way, that I should seriously consider an alternative?
Should we take this conversation to private messaging?

[Davey-T]

I think it's worth trying to seal the existing structure before replacing it, being of a similar age as yourself we hardly need something that will " last a lifetime " 😁

Whatever system you decide on any of the various resins with / without fiberglass reinforcing really need to be done in warm weather especially on a sloping roof.

I've done flat roofs with fiberglass resin, just mix it in a bucket , pour it on and spread it out and don't think they would be very easy to apply on a slope.

Maybe a compromise of taping the joints then overcoating the rest.

Dave

[Rusted]

Thanks Dave.

Though I fear you underestimate the problem.
After some early imaging, this morning, the sky turned dark and started tipping down.

To the thunder of wind-driven rain on plywood, I could add the steady plops of water.
Dripping into large containers arranged on the floor.
Which already have an inch of water from yesterday's deluge.

If it gets any worse I shall become a poor imitation of an aquarist.
Rather than a poor imitation of an amateur astronomer.

I am committed to fitting a plastic lid on my octagon.
Life is indeed far too short to be wasted on precious, summer months of sanding and painting.
Only for it to be required all over again next year.

The cost of replacing all my kit after a single drenching would soon exceed that of a new dome.
The trapezoidal dome was great fun to build but has proved that GRP is vital to waterproofing ply.
Now I shall cut out the middle man and go straight to the finished GRP jobby.

Any Dane who wants a free 3m dome, to fibreglass themselves at ground level, can take it away.
It will be in segments on the ground [for a while] to be quickly removed by those who want it. NO time wasters!
I built it that way so it would always come apart.
Hundreds of hex socket stainless steel, machine screws and SS washers hold the ribs together.

With the Pulsar I gain thermally on better seeing, ease of use, waterproofing and improved user comfort.
A replacement base ring is all I need to support the new dome's low, rotation wall at the existing sill level.
I can retain everything I have built so far with only the loss of about a foot on diameter at base ring level.
My ply dome has deeper ribs so the difference in useful diameter isn't really that great.

[Bukko]

Just picked up on this tread and me being quoted.

The decision to go with the Scopedoome was a close one, but on reflection, I think it was right for me.

My rationale behind going for the Scopedome instead of the Pulsar was more to do with my application. I installed a .4m OO ODK and when I did the numbers, the shutter width on the Pulsar was very tight - 0.7m vs 1.0m Probably OK with an alt-az mount, but with an ME2, when slewed round, the shutter width was too tight.

I also wanted to mount it at elevation and if I used the Pulsar half height only, I would need to add a lot more brickss (and therefore thermal mass) to the installations. But when looking at the full height dome from Pulsar, including the motors, etc. the difference was not that much. Then it would need to be transported to France and the shipping costs are high (crossing the channel with a truck is expensive)

The Scopedome is a three metre sphere, so quite a lot bigger than the Pulsar 2.7m. Yes, the whole dome rotates, instead of just the top as in the Pulsar. Having a long refractor might actually suit the Scopedome more but if you are seriousy considering one of these domes as your solution, research them both carefully.

Oh, being GRP, I do get some condensation build up and use a de-humidifier to keep it under control.

If you think I can help further, I promise an impartial response, based on my own research and experience.

Gordon

 

[Rusted]

Thanks Gordon.

The 2.7m Pulsar drop-on lid suits me just fine. I wanted one when I first started my build.
At that time I was still using my 7" f/12 as a straight tube and it was tight fit even in my larger dome.

Bresser-De are the European distributors for Pulsar now. Very short delivery times are promised.
I'm looking at €70 [website auto-quote] for home delivery from Germany to Denmark.
The bank holiday weekend has intervened in ordering progress.

PULSAR 2.7 METRE OBSERVATORY SHORT HEIGHT | Bresser

I'm hoping I can build the dome in place like I did my own ply and timber dome.
Failing that I can hire a telescopic lift for the whole dome. [Prefer not to.]
I built my own dome "upstairs" in segments using braced, builders stepladders.
So I think I can manage the 2.7m on a still day.

Pulsar really ought to provide individual panel weights on their website, but don't.
Customers could then judge how much voluntary help they need on the big day.

Has anybody actually weighed their 2.7m bits and bobs prior to or during assembly?
Any opinions on a one man band build 14' off the ground? 

[Rusted]

I should have added that a stumpy tine, fork mount would add useful headroom for a longer OTA.
Without the present considerable GEM offset I'd then have room to spare.

Some completely unnecessary illustrations of the original build and my techniques for working alone up high:

Edited June 7, 2020 by Rusted

[Bukko]

51 minutes ago, Rusted said:

Thanks Gordon.

The 2.7m Pulsar drop-on lid suits me just fine. I wanted one when I first started my build.
At that time I was still using my 7" f/12 as a straight tube and it was tight fit even in my larger dome.

Bresser-De are the European distributors for Pulsar now. Very short delivery times are promised.
I'm looking at €70 [website auto-quote] for home delivery from Germany to Denmark.
The bank holiday weekend has intervened in ordering progress.

PULSAR 2.7 METRE OBSERVATORY SHORT HEIGHT | Bresser

I'm hoping I can build the dome in place like I did my own ply and timber dome.
Failing that I can hire a telescopic lift for the whole dome. [Prefer not to.]
I built my own dome "upstairs" in segments using braced, builders stepladders.
So I think I can manage the 2.7m on a still day.

Pulsar really ought to provide individual panel weights on their website, but don't.
Customers could then judge how much voluntary help they need on the big day.

Has anybody actually weighed their 2.7m bits and bobs prior to or during assembly?
Any opinions on a one man band build 14' off the ground? 

The Scopedome is only 5 panels and the bigger ones took two to carry and three to fit (at only 800mm off the ground). I really would not fancy lifting the bigger panels as high as you have built. Even though I would expect the Pulsar panels to be lighter, one-man build is not really a good idea. As you have a lot of the structure in place, could you install a lifting rig with a pulley to bring the panels up? Also, what working room do you have around the exterior?

As to the delivery charge, I also bought mine through the Germaan distributor and the delivery was significant. The online charge was low, but on application, jumped a lot. When you ask, expect it to be closer to a thousand Euros..

Gordon

[Bukko]

Oh, just followed the link to the Bresser site.

Delivery will only be a few days, but when I enquired of both Pulsar and Scopedome, the manufacturing was a couple of months' lead time. The website also says they need to engage a forwarding agent so forget the Eur70. Are you also adding the automation kit? When added together, this is whaat pushed the Pulsar costs close to the Scopedome for me.

I also saw your earlier post with the pictures. Looks like there is room on the outside, assuming your existing dome is a similar size to the Pulsar.

Good luck,

Gordon.

[Rusted]

Thanks Gordon.

We shall see what they say when Bresser are back in the office.
They surely can't claim a few days to deliver if they have no stock?
That would be called false advertising. Likewise, the delivery fee.
It would have to be "ballpark" or it would be false advertising.
Or click bait.

There are national and European laws covering false advertising.
Not to mention the bad press on the specialist astro forums.
That's an extremely narrow customer base to be messing about.

Absolutely no plans for automating the dome at that price!
Besides, I only need a nudge now and then for solar imaging.

I have all the lifting equipment I need from the last build.
Chain hoists, boat winches and several yachting block and tackle sets.
My dome is 3m Ø. So the 2.7m would, probably just about fit inside.

I need a slightly smaller base ring to support the Pulsar rotation ring properly.
Other than that and careful levelling I see no real problems on a still day.

Edited June 7, 2020 by Rusted
typo

[Bukko]

Don't think it is false advertising...

They talk about shipping period of a few daays, but point out they cannot accept an order vias the website. I really doubt they keep them in stock, so will be really interested to find out what they say.

For delivery costs I quote the site:

"This article cannot be ordered online! Delivery by forwarding agent requires an individual agreement. Please contact us by phone or e-mail for further information!" I was going to purchase direct from Pulsar and have a carrier bring it over and the manufacturing lead time was a couple of months or more. No idea what covid-19 has done to this so don't be upset if the manufacturing lead is longish...

And I understand what you say about the automation costs. But you can always retrospectively install later, even if you only do the dome rotation motor.

Gordon.

[Rusted]

Thanks Gordon.

You will be the first to know the truth once I hear from Bresser.

As will everybody else here of course.

The price for a fully automated Scopedome is indeed very close to a Pulsar with all "the hidden extras."
The Scopedome just doesn't appeal for my unique situation.

I would have to rebuild the entire structure from the ground up to make it fit.
The Pulsar is a simple, flip-top head job for my particular build.

I get to keep my building with everything I have tailored and improved since I built it.
Security, access, monitor and electronics, Wifi, swivel chair and imaging desk wrapped around the isolated pier.
Nothing changes except I will no longer need a bathing cap. 
 

[Bukko]

6 minutes ago, Rusted said:

Thanks Gordon.

You will be the first to know the truth once I hear from Bresser.

As will everybody else here of course.

The price for a fully automated Scopedome is indeed very close to a Pulsar with all "the hidden extras."
The Scopedome just doesn't appeal for my unique situation.

I would have to rebuild the entire structure from the ground up to make it fit.
The Pulsar is a simple, flip-top head job for my particular build.

I get to keep my building with everything I have tailored and improved since I built it.
Security, access, monitor and electronics, Wifi, swivel chair and imaging desk wrapped around the isolated pier.
Nothing changes except I will no longer need a bathing cap. 
 

I agree - The Scopedome needs a dead flat and level base within 1mm. I was going to build it on a wooden platform but decided against it as the engineering grew a lot. Wood moves and if bolted down, might warp the base rings and stop it revolving smoothly. At your elevation, I would think this would be even more difficult so it is probably best not to do it, unless you want to put in some sort of rigid platform to build off.

I am sure you did not plan for this change, especially after you have put in so much work on your original dome, but unless you can waterproof it, damaging the scope, electronics, etc. would be a hobby killer.

Gordon.

[Rusted]

Thanks Gordon.

I look straight across at the dome from my upstairs computer window.
Sadly, the dome is looking less than smart since the paint started peeling.
The birch plywood surface is getting very rough in places from water penetration.

A hired, telescopic lift would get it back down for a fibreglass overcoat on the ground. 
The work involved just does not appeal at all. It had its chance and it simply failed to last.

Time to move on without regret. It was enjoyable and demanding work to build.
So it owes me nothing but fond memories of a successful project which still fills me with pride and little awe.
Those who consider a plywood dome should factor in the fibreglass coating as vital to longevity.

It completely revolutionised my observing and now I am imaging quite successfully after decades in the doldrums.
Those without an observatory cannot possibly imagine the value a dome brings to observing and imaging.
I can be imaging in a couple of minutes from scratch and walk away knowing it will come to no harm.
I go indoors for meals and it will all be there, ready and without any delay, when I return.
This is invaluable in cloudy weather because I can sit and browse in comfort until the sun reappears.

Whole days pass as I quietly capture videos and images without ever leaving home.
That is absolutely priceless to someone who is retired. It gives real meaning to my life and I am always within earshot of my wife.
An ROR would need constant supervision in changeable weather and provide absolutely no shelter from the burning sun.