Skin material for dome

[cloudnine]

Hi folks,

Imagine a Terry's chocolate orange (other chocolate oranges are available), cut it in half at the 'equator', and reduce the number of segments to, say, eight fat segments. Each segment can be covered by something flat that curves from the equator to the pole. Hold that thought!

I'm toying with the idea of building my obsy, with dome, etc... While I think this is very achievable the one single snag I can't get my head around is what to use as the dome skin. 

Does anyone have any recommendations/experience of the best skin material to use to clad the segments? I am working my way through many old threads, but answers/shortcuts very much appreciated.

Many thanks,

Martin

P.S. Am not sure whether this is the most suitable forum for this question, but the DIY Observatories seems to be locked.

[Charic]

Hi cloudnine.......What about fish pond liner, made of Butyl Rubber, or standard shed roofing felt, you could fabricate seals over your structures joints, then cut tiles to fit  and overlap the seals, using standard roofing tacks. I've got a 6x4 shed that I'm considering to convert, but I'll just have a folding roof, or sliding?

[SnakeyJ]

Fibreglass or Casco sheath?

Ruberoid roofing membrane?

I was toying with the idea of stretched canvas, painted over - this was used quite a lot in traditional boat building to waterproof the uppers.

[Peter Drew]

I've always used 18swg aluminium for my domes but this is now a very expensive covering. I have seen thin plywood and even hardboard used, well painted and maintained these can last a surprisingly long time. 

[pete_l]

I suppose the biggest factor will be the material you use to make the segments from: wood, ply (different properties from wood), glass-fibre, metal ?

As a starter for 10, have a look at an epoxy paint - but bear in mind the surface preparations required for your base material.

[keithatrochdale]

How are you going to do the shutter for observing?

.

[cloudnine]

Thanks all for the ideas thus far. The framework will be ply, whereas I haven't exactly decided on the shutter system yet. In the back of my mind I'd love to do a Palomar-style shutter which split in two and opens sideways which avoids a number of issues and adds a few more (mostly bike-chain-related). It might be a bit much  but I reckon it's doable. Don't quote me.   The alternative is the classic up-and-over. It's early days. Am currently dismantling an old shed and planning on laying oversize foundations (to allow a walk-way round the dome). In my head I know what I want to achieve but it's too fluid to write down at the moment. 

The cladding/skin of the dome is my biggest bugbear. I had thought about marine ply, but the only local source has it 9mm thick which is impossible to bend to the form. The dome will likely be 2.5m diameter (a gap in the market which seems the best compromise between space and volume). 

Will happily accept more suggestions, especially how to treat the cladding to make it weather-proof.

Cheers,

Martin

[stash_old]

Don't know the price but would work for dome and/or sides.

http://www.concretecanvas.com/

[Bizibilder]

I would suggest fiberglass - maybe over an underframe of ply and hardboard.  A thin coat of glass with a light matting inside and out would work as long as it was sealed properly - the only downside would be cost as fiberglass is surprisingly expensive!

[ollypenrice]

Thin flat galvanised steel sheet? I used this recently to make a permanent parasol affair on a terrace. It's very durable and cuts with a small angle grinder.

I have to say that I think domes are hard work and the wrong shape, when small, because only the scope has any headroom!

Olly

[olawelin]

Hello, I used fiberglass and polyester for my 2.4m dome and painted it with boat paint, works great!

http://stargazerslounge.com/topic/150317-building-observatory-with-dome-in-southern-sweden/

Ola

[skybadger]

Hi Martin.

Commercial domes are available in 2.2,2.4,2.7 and 3,4.5,5 and 6m sizes from different vendors so I am wondering why you think 2.5m is a gap ?

Mike

[cloudnine]

Hi Mike,

One vendor does 2.2m, 2.7m and 3.5m

Another vendor does 2.3m, 3.5m, 5m, 6.7m

I'm tall so from experience I find that 2.2m (actually 2.1m) will probably be a bit cramped after a while. 2.3m is outside my price range. 2.7m is too big and expensive.

Who does the 2.4m dome? If you mean skyshed then it's not quite my cup of tea. Also looking at pictures online the thick walls implies the internal dimension is a lot less. I'm no expert on any of this so I'm happy to be corrected.

Cheers,

Martin

[Garethr]

Martin

I'm using composite Ali panels for the walls of my Obsy. They consist of two thin Ali panels with a thin layer of foam between. Not sure where you live but I will probably have 6 or 7 left over each being 8x4

Gareth

[cloudnine]

Hi Gareth,

The Ali panels with the foam sounds an interesting idea. I noted this with interest from your 'Home build observatory' thread. I'm probably 4-6 months behind you in terms of build as I'm demolishing old sheds and starting to do the groundwork (my garden slopes substantially, hence need retaining walls, etc.... which needs to look acceptable to the powers that be).

Are the panels bendy at all, i.e can they be used to clad the lower (cylindrical) observatory wall?

Martin

[alan687]

have you considered a canvas, ive never seen it done before but i think it would make a good job. as an example, the material used on microlight wings, its light, waterproof, can be painted and can be stretched.

im sure there is a similar material out there that wouldn't be as expensive, it could be stretched around the dome in sections.

just an idea

[Garethr]

Martin. Yes they are very flexible and should work. Just seen where you live so it's a bit far to travel.

[cloudnine]

No worries, Gareth. I wasn't expecting anything 

Is the ali-foam-ali an off-the-shelf product? I recall reading that they were from advertising hoardings or something?

[cloudnine]

Hi Alan,

If canvas can be made to be quite tough, and not flap around in gales then it's an option. I'm on the side of an exposed south-east facing hill with the winds channeling up the Otter Valley uninterrupted until it reaches my house. Even on days with light breeze it can be surprisingly gusty.

I'll add it to the list of things to investigate.

Martin

[JamesF]

I seem to recall reading a web page describing how someone had made their dome using cement render.

James

[JamesF]

Here it is.  This is more of a geodesic design, but I'm sure the same principle could be used in your case:

http://www.starshed.net/obs/thedome.htm

James

[cloudnine]

Cool. A stucco geodesic dome. Food for thought and yet another website full of useful tips and tricks.

Many thanks!

Martin

[JamesF]

On a practical level I mostly agree with Olly that small(-ish) domes aren't that practical, but life doesn't always have to be about what's practical and if I were going to build a dome I'd love to make a geodesic one.  I want two piers in mine though and that really does make a dome rather more awkward (and far too interesting to the planning authority).

James

[Garethr]

Martin.

Yes that's where I salvaged them from. As for flexibility I tried one in the garden this evening and managed to bend 1 sheet into a circle(slowly) so possibilities there. Have used a couple to infill the bottom of SWMBO greenhouse as these areas will not be accessible once Obsy is built so replacing cracked glass is gonna be difficult Worth keeping an eye on any local builds going up and asking when they are finished if you can have them. In the construction industry any items recycled is a bonus to the client and contractor as the don't have to to dispose of them but can claim they are recycled.

[alan687]

Hi Alan,

If canvas can be made to be quite tough, and not flap around in gales then it's an option. I'm on the side of an exposed south-east facing hill with the winds channeling up the Otter Valley uninterrupted until it reaches my house. Even on days with light breeze it can be surprisingly gusty.

I'll add it to the list of things to investigate.

Martin

if it was stretched and secured properly the wind would not be an issue, only problem i would see with it would be security.

Like i said before just an idea but sometimes you have to think outside the box for a good idea.