Constant damp weather

[Tinker1947]

I don't know if it would work but i would stick bubble wrap to the inner walls......

[Oddsocks]

The last few months have been particularly bad for condensation with high humidity levels right across the UK, recently I had to bring all of my engineering tools and diy power tools indoors from the garden shed as everything out there was running with water.

Control of condensation in a single skin observatory needs more than one method of attack.

Adequate ventilation is important and normally there will be sufficient airflow through the gap between the walls and the dome but if the observatory is in a very sheltered location or surounded by shrubbery and not exposed to the wind then the ventilation through the gap will be insufficient. A 4" solar powered caravan fan on the south facing wall set to blow air in to the observatory will provide good airflow for at least five hours a day and will help to keep the air moving.

A waterproof membrane should be laid across the floor, below any floor covering, to prevent damp rising from the ground below, raised decking seems particularly good at allowing dampness to permeate from below, much more than solid concrete which I found suprising so a well-sealed floor membrane is a must.

Thermal insulation of the walls and dome will reduce condensation on those surfaces and the least expensive way is a film of bubble wrap applied using double sided tape, normal packaging bubble wrap is way to flimsy and wont last but the stronger metalised polyester bubble foil sold in DIY stores for insulating roof spaces and dry-lined walls is great for this and is not too heavy for double sided tape to hold it in place. As long as you take care not to bang into the walls while using the observatory then this material will last many years.

A better looking alternative is the self-adhesive thermal-accoustic matting sold for application to the walls and roof linings of cars and vans, this can be closed cell foam with or without a metalised foil facing, easy to keep clean but easy to tear and damage or plain open-weave matting which is stronger and usually finished in matt black but needs regular vacuuming to keep clean.

Stopping condensation forming on the scope, mount, power supplies, computers etc is not easy, good ventilation will help but can only go so far, a small 150w frost protection heater of the wire element type set to 5 deg will improve things, avoid the oil-filled radiator types, they take much too long to cool down when you open the observatory and switch them off, the wire element type will cool in fifteen minutes.

Scope covers used inside the observatory should be fully breathable, the waterproof covers sold to protect scopes in the open are totally unsuitable since they trap moisture inside the cover and stop it evaporating away.

Finally a dehumidifier is a must for most observatories, it does not need to run continually, though you can set many of them to monitor and maintain a set humidity this can be a rather costly undertaking in fuel bills, in my old Skyshed Pod I ran a dessicant type dehumidifier for one hour each day and used an environmental data logger to see what was happening, after one hour the humididy in the observatory had dropped to below 20% and 23 hours later it was back up to 60% but this was enough to keep dampness at bay.

My Skyshed POD already had thermal insulation in the walls and fixed half of the dome but condensation used to form on the un-insulated lifting section of the dome and drip on the floor before I began using the dehumidifier.

My Pulsar observatory is due for delivery in a months time and I will be lining it with self adhesive open weave thermal-acccoustic car matting @ £7 per square metre, fitting a mains powered trickle fan in one wall (observatory receives no direct sun for most of the year so solar fan would be no good for me), the scope cover is an old heavy wool blanket and I will be using the frost protection heater full time plus dehumidifier for an hour a day.

A safe, permanent, mains power supply to the observatory is a must if you are going to use frost protection heaters and dehumidifiers etc.

William.

[gnomus]

Thank you for this detailed post. I am currently using a (not-plumbed-in) dehumidifier. I have had a couple of nights when, with the roof off, I have had water running down the walls of my observatory. Do you think your thermal acoustic foam would help with this? Also, I did a search for 150 watt frost heaters - jings there are a lot of them about (although I didn't find many that were 150 W). Do you have any specific recommendations for a heater and for the foam?

Thanks again.

Steve

[Tinker1947]

Thank you for this detailed post. I am currently using a (not-plumbed-in) dehumidifier. I have had a couple of nights when, with the roof off, I have had water running down the walls of my observatory. Do you think your thermal acoustic foam would help with this? Also, I did a search for 150 watt frost heaters - jings there are a lot of them about (although I didn't find many that were 150 W). Do you have any specific recommendations for a heater and for the foam?

Thanks again.

Steve

Heating a ventilated room or obby in this case is like throwing money out of a open window, the cause is the temperature on a single thickness wall, get the wall double up and the running water will go away, if i had a Dome i would fibre glass the walls then clad them in 12mm T&G, the dome its self would need similar treatment the shape is a real pain but as a single sheet of fibre glass its a dew magnet.....

[gnomus]

Heating a ventilated room or obby in this case is like throwing money out of a open window, the cause is the temperature on a single thickness wall, get the wall double up and the running water will go away, if i had a Dome i would fibre glass the walls then clad them in 12mm T&G, the dome its self would need similar treatment the shape is a real pain but as a single sheet of fibre glass its a dew magnet.....

My observatory is a ROR with an interior wall lined with plywood.

[tteedd]

Hi Oddsocks and Tinker

Many thanks for the advice.

T&G?

This morning the Obs' is dry, dehumidifier tank 1/3 full. So it seems that I have a temporary cure. Mind you it was not so cold last night. 2ndry mirror seems clear in daylight so perhaps I was imagining things in my alarm - or my dryer was not up to clearing it properly.

The weather in general through the autumn has been windy and wet rather than still and cold which is probably why I have not suffered before.

I'm off to B & Q to get an outside socket. I've needed one for years (with a petrol mower I've not felt the pressure to fit one) but I do not like cables trapped in doors or windows overnight.

My intention for power was originally to replace the garden shed behind the observatory with a new one (astro-shed). Fitting solar panels to it's S facing roof. The cables from the observatory to this location are already in place. I did not really want 240V in the observatory. I felt I could power everything I wanted from 12 & 24V dc.

I had intended to paint the inside black but will now consider an insulation layer first. May also fit a fan. But I'm not sure I want a heater, probably a waste of energy but I do want to leave the scope and equipment fitted so will, in the end, do whatever is necessary.

[Tinker1947]

My observatory is a ROR with an interior wall lined with plywood.

Same as mine, appears to be dry as a bone, even the poloycarbonate roof, the old ply plus rubber always had some drips on it.....

[Tinker1947]

Hi Oddsocks and Tinker

Many thanks for the advice.

T&G?

This morning the Obs' is dry, dehumidifier tank 1/3 full. So it seems that I have a temporary cure. Mind you it was not so cold last night. 2ndry mirror seems clear in daylight so perhaps I was imagining things in my alarm - or my dryer was not up to clearing it properly.

The weather in general through the autumn has been windy and wet rather than still and cold which is probably why I have not suffered before.

I'm off to B & Q to get an outside socket. I've needed one for years (with a petrol mower I've not felt the pressure to fit one) but I do not like cables trapped in doors or windows overnight.

My intention for power was originally to replace the garden shed behind the observatory with a new one (astro-shed). Fitting solar panels to it's S facing roof. The cables from the observatory to this location are already in place. I did not really want 240V in the observatory. I felt I could power everything I wanted from 12 & 24V dc.

I had intended to paint the inside black but will now consider an insulation layer first. May also fit a fan. But I'm not sure I want a heater, probably a waste of energy but I do want to leave the scope and equipment fitted so will, in the end, do whatever is necessary.

T&G = Tongue & Groove timber

[Davey-T]

Thank you for this detailed post. I am currently using a (not-plumbed-in) dehumidifier. I have had a couple of nights when, with the roof off, I have had water running down the walls of my observatory. Do you think your thermal acoustic foam would help with this? Also, I did a search for 150 watt frost heaters - jings there are a lot of them about (although I didn't find many that were 150 W). Do you have any specific recommendations for a heater and for the foam?

Thanks again.

Steve

I use one of these with a plug in thermostat.

Dave

http://www.qvsdirect.com/2ft-120w-tubular-heater-with-wall-brackets-white-ip55

Edit: cheaper on EB

[Astroboffin]

My observatory is a ROR with an interior wall lined with plywood.

So why would you have water running down the walls with the roof off.....very strange, that should never happen

If warm air hits a cold surface then yes it will condense and run down, but with your roof open I can't see why or how air would condense on the interior walls....as soon as you open the roof, within a few mins the temperatures would equalise.

Even if the inside of your obsy was very warm, it would not condense on the inside walls unless they were very cold, and with wood, that's not usual.

Scratching my head....

AB

Edit: sorry just re read your post, you have a dehumidifier running and the warm air from that is condensing on the interior walls, makes sense now, forget the dehumidifier you do t need one, just ventilate your obsy properly and all will be fine, as long as it is 100% watertight.

I think people who use dehumidifiers have a big ventilation problem, if not enough ventilation you will get damp, and you are dealing with the damp by using a dehumidifier, solve the damp problem at the source.....more ventilation...simples...:)

AB

[gnomus]

So why would you have water running down the walls with the roof off.....very strange, that should never happen

If warm air hits a cold surface then yes it will condense and run down, but with your roof open I can't see why or how air would condense on the interior walls....as soon as you open the roof, within a few mins the temperatures would equalise.

Even if the inside of your obsy was very warm, it would not condense on the inside walls unless they were very cold, and with wood, that's not usual.

Scratching my head....

AB

Edit: sorry just re read your post, you have a dehumidifier running and the warm air from that is condensing on the interior walls, makes sense now, forget the dehumidifier you do t need one, just ventilate your obsy properly and all will be fine, as long as it is 100% watertight.

I think people who use dehumidifiers have a big ventilation problem, if not enough ventilation you will get damp, and you are dealing with the damp by using a dehumidifier, solve the damp problem at the source.....more ventilation...simples... :)

AB

I also painted the walls with some bathroom paint.  I did this because of the mould resisting agents in bathroom paint.  Although I went for  matt finish it still has a 'satiny' look to it.

I should also add that generally I have no issues of this sort.  It has happened twice when RH and dewpoint were very close together.

[Gina]

Arranging good ventillation without the rain blowing in is not easy.

[Garethr]

I think my problem is that there is so much moisture in the air. Ventilation isn't the problem when the wind blows I can feel the air moving inside its just the air contains so much moisture.

Gareth.

[Astroboffin]

I also painted the walls with some bathroom paint.  I did this because of the mould resisting agents in bathroom paint.  Although I went for  matt finish it still has a 'satiny' look to it.

I should also add that generally I have no issues of this sort.  It has happened twice when RH and dewpoint were very close together.

The problem with bathroom paint is that it is not breathable, you should use "new plaster paint", as it allows moisture in and out so no issues.

I will guess that eventually that paint will lift and blister...the wood should be allowed to breath, the paint might stop mould on the surface, but will nor stop it from inside or behind the wood, if any damp gets between your layers of wood on your obsy walls, it will get trapped, especially if you have a non breathable membrane on the outside of your obsy.

It sounds like all bad news, but easily solved with more ventilation, my shed is full of holes but water can't get in, and never had a drop of moisture on anything, ever.

AB

[Astroboffin]

I think my problem is that there is so much moisture in the air. Ventilation isn't the problem when the wind blows I can feel the air moving inside its just the air contains so much moisture.

Gareth.

But that will in turn be moved back our through the ventilation, it need to have a constant movement of air in and out, for it to work.

As long as the inside and outside temps are similar then no issues, but if you have heat inside then you will cause condensation.

You don't want that moisture you mention, to condense......

So ventilation and no heat, to keep inside and outside temps almost the same, but it has to be completely waterproof, that is the key here.

AB

[Garethr]

True but I think the timbers are sucking up the moisture as it passes by.

[Stub Mandrel]

But that will in turn be moved back our through the ventilation, it need to have a constant movement of air in and out, for it to work.

As long as the inside and outside temps are similar then no issues, but if you have heat inside then you will cause condensation.

You don't want that moisture you mention, to condense......

So ventilation and no heat, to keep inside and outside temps almost the same, but it has to be completely waterproof, that is the key here.

AB

I bet you wear a kilt

[Astroboffin]

I bet you wear a kilt

No a skirt.....

[tteedd]

Back to my wet old style pulsar observatory!

And thanks to William (Oddsocks) for his detailed reply.

I have had the de-humidifier in for a few weeks now and have experimented with ventilation (jacked the dome up to allow airflow). Neither totally conclusive. I still get condensation in the top of the dome but my equipment seems to stay dry in either case.

One thing I have noticed, opening up in day time, the scope is usually colder than the outside air/or surrounding air and subject to instant condensation when the cover is removed.

It seems that I am at the parting of the ways and have two options.

1. Put in large amounts of ventilation to ensure inside and outside temperatures are near equilibrium.

2. Install de-humidifier and heater (or aircon).

The second means a mains power supply and the end of my scheme to run totally on dc from solar panel and batteries.

Either way I think I also need to try and insulate the inside of the dome.

More comment from anyone with experience of a GRP observatory, particularly and old Pulsar model, would be welcome.

Meanwhile when I am away and unable to monitor the situation I will bring the scope indoors.

[Tinker1947]

Insulate the dome walls will stop condensation its that simple, well the idea is i have suggested sticking bubble wrap to the walls and dome, not seen anybody having tried it yet though......

[Astroboffin]

Back to my wet old style pulsar observatory!

And thanks to William (Oddsocks) for his detailed reply.

I have had the de-humidifier in for a few weeks now and have experimented with ventilation (jacked the dome up to allow airflow). Neither totally conclusive. I still get condensation in the top of the dome but my equipment seems to stay dry in either case.

One thing I have noticed, opening up in day time, the scope is usually colder than the outside air/or surrounding air and subject to instant condensation when the cover is removed.

It seems that I am at the parting of the ways and have two options.

1. Put in large amounts of ventilation to ensure inside and outside temperatures are near equilibrium.

2. Install de-humidifier and heater (or aircon).

The second means a mains power supply and the end of my scheme to run totally on dc from solar panel and batteries.

Either way I think I also need to try and insulate the inside of the dome.

More comment from anyone with experience of a GRP observatory, particularly and old Pulsar model, would be welcome.

Meanwhile when I am away and unable to monitor the situation I will bring the scope indoors.

The ventilation need to really be at the highest and lowest pointsto get the full effect.....

[Astroboffin]

Insulate the dome walls will stop condensation its that simple, well the idea is i have suggested sticking bubble wrap to the walls and dome, not seen anybody having tried it yet though......

That won't always stop it, but delay it, the walls will still cool and any warm air can still condense on the bubble wrap, especially with it being plastic and certainly not breathable, but if you have heat in the obsy then insulation will be good, but for cheapness and ease, just ventilate top and bottom and keep it water tight...and all will be good....simples

Also dehumidifiers will probably work but why go to the expense when you should treat the damp at the source and not just try and get rid once it occurs.

AB

[Stub Mandrel]

If the problem is damp condensing on the equipment when the dome is opened in the day, insulation will make the problem worse by delaying the warming of the interior.

Free passage of air will help balance the temperatures, so insulation with ventilation might be a cure.

I'm learning that this is very different from a workshop, which it is possible to keep nearly airtight, if well insulated and temperature controlled. The gap between my workshop and the utility room is covered but not sealed and can be a sauna of steam with the tumble-drier working, but this never seems to trouble my tools. Very different If I was to open the roof!

[Oddsocks]

Insulate the dome walls will stop condensation its that simple, well the idea is i have suggested sticking bubble wrap to the walls and dome, not seen anybody having tried it yet though......

http://www.iankingimaging.com/show_article.php?id=22

[yesyes]

I seem to have no damp inside the scope room or warm room without running a dehumidifier or heater. The roll off roof has a gap all around for ventilation with some overhang to stop rain coming in.

What I do start to get problems with is the T&G cladding on the front. With this weather the timer has been wet / damp for months now and it's starting to turn grey. I have only treated it with clear wood preserver and teak oil because I like the natural look of the wood. I think I will have to paint it once it has completely dried out.