Observatory building materials

[Ivor]

I'm trying to decide on the best material to build an observatory from, in particular the dome. From my research so far a big concern is internal condensation so any design needs to minimise the creation and allow it to drain off outside easily. My initial idea was to use a mix of plywood and MDF however thinking on I'm now concerned about its ability to absorb water and also the likelihood of warping causing the dome rotation deteriorating over time.

I'm now looking for alternative materials I'd prefer to use one material but with different thickness for both aesthetics and ease. My current idea is to have a rigid frame (~5-8mm thick) and then use a thinner version (~3mm) to allow flexure when covering the frame.

So before going any further, am I worrying too much about using wood based materials?

On my internet travels I've see various materials used none of which I have personal experience of so I'm looking for some ideas.  There are numerous Plastic/ PVC/ Polypropylene/ Acrylic/ Polycarbonate materials out there but before going to a supplier I was hoping to find someone with experience of dealing with these materials so I know the right questions to ask.

For example what about these material?

http://www.plasticsheets.org.uk/palopaque-gloss-white-pvc-8-x-4-sheets-1783-p.asp
http://www.plasticsheets.org.uk/polypropylene-sheet-black-1565-p.asp

[Mac]

From my research so far a big concern is internal condensation

Huge bug bear, the only way i've managed to get around the condensation is to have a heater on permanently,
its set for about 8C,

and an auto himidity fan set to half way,
so far. There dosent seem to be too much condensation on the roof, or in the laptop.

My other problem at the moment is water ingress from the split dome and under the floor, but thats another matter.

Mac.

[Carole]

I have a dehumidifier (DIO) going most of the winter and get no problems at all with condensation.  I leave everything set up from one session to another including the camera. 

Carole

[RobertM]

Not had any moisture in my wooden roll off bar any that gets in while I'm imaging.  In fact even condensation on the tube/mount etc from the previous night is more often than not gone when I look in the morning.  It has to be a very cool humid night (light fog) before the wood gets even remotely damp.   One or twice I have had condensation but it's been nothing to worry about.

Robert

[Ivor]

I don't have the space for a ROR and I believe the condensation issues are more prevalent in a dome.

I think a dehumidifier is unavoidable, but I'd like to minimise its workload by picking the right materials.

I looked at pulsar dome at the weekend it's designed to allow internal condensation to roll off outside.

[MarkH]

Hi Ivor, some time ago I made a dew sheild from heavy daler card for want of something easy do work with. What I didn't realise at the time was that it was an unexpected good choice. Firstly it doesn't get cold to the touch, secondly it doesn't get any condensation forming on it at all. What happens is it becomes slightly damp and slightly soft. The following day it is always dried out and back to normal. So it  may be a good idea to line the roof with something similar that is absorbent.

[mickw]

If the card is getting damp it's absorbing moisture.
Polystyrene is cheap and easy to work with.  If the observatory is going to be lined with a sheet material (plywood/hardboard or whatever) fibreglass will do the trick.

[MarkH]

Yes Mick that was the point of my post that absorbing the moisture prevented it forming as condensation in  the form of droplets and dripping onto the lens.

[MarkS]

I echo Robert's remarks.  My wooden observatory had no condensation problems.

At least it didn't until the roof was forced into its pathologically retracted position.  The interior then got pretty wet: