Advice wanted on thickness of concrete for POD, etc

[broadway1]

I've managed to secure a second-hand 3-bay Skyshed POD that I will take delivery of in a couple of weeks time, with the intention of having my Edge 11 and W.O. FLT110 mounted on a (still to be delivered) EQ8 on a tripod inside. Next step is to put down a base for the POD to stand on, and I would like any advice on thickness (and possibly construction) that you could recommend.

If you have had a contractor put a similar base in recently, I would be interested in how much this cost you.

Clear skies,

John

[Earl]

Decking for the pod and a concrete peir pedestal, if you check the altair astro site they have some examples to look at also the pod website.

[Bizibilder]

I would suggest a base of at least 6" of concrete, preferably on a base of good hardcore.  However I would not suggest putting the mount on a tripod - as you are building a base you can easily install a pier.  To do this you will need to make the base in two parts.  Firstly a block of concrete, around 2' cube in the centre - this is cast into a hole so it ends up level with the final floor).  This will need some bolts in it to hold the pier.  The rest of the base is poured around this block but without touching it (most folk put a layer of something between the two "pours" of concrete, like expanded polystyrene or builders foam - especially made for making expansion gaps in concrete).  The "gap" only needs to be around half an inch.  The pier is then bolted to the central block and your Pod is fixed to the main base.  The reason for having the gap between the two concrete parts is to prevent vibrations from things like yourself walking about being transmitted to the mount.  Hope this helps - please ask if you want more details.

You can buy a pier or have one made by your local steel fabricator (much cheaper!!!).  Altair astro also sell the correct adhesive for sealing the Pod to the concrete.  (PS Concrete - even if poured professionally - can be relativly cheap and once down is maintenance free).

[broadway1]

Thanks for your comments so far. Please be tolerant, but I prefer to stick with my plan to use the tripod. Information on the depth of concrete and hardcore to use is most helpful, as is the idea of the use of sealant to seal the POD to the concrete - I must have missed this on the Altair website - is this easy to remove or does it set rock hard?.

Anyone got any actual cost data?  I am concerned I will end up paying a "Surrey" premium, based on the one quote I have had so far.

Clear skies,

John

[Bizibilder]

You may find that hiring a mixer for a day would be cheaper - unless you are very fit and used to hard labour!!

[broadway1]

Unfortunately for me, I had a mild stroke back in September, so I am not prepared to attempt making a concrete base myself.  However, so far this hasn't put me off imaging, and it did lead to my wife finally saying I could have an observatory ! So not all bad lol.

Latest image at: http://www.flickr.com/photos/29838100@N02/10573060544/

Clear skies,

John

[dmahon]

I'd use 6" of concrete poured directly onto compacted ground - if it's not, then put 3-4" of compacted (hire a whacker plate) hardcore down first. If going directly onto compact earth, make the edges a few inches thicker (ie dig deeper around the perimeter).

My advice:

Get readymix (minimix) in if access permits

If access doesn't permit, get readymix and hire a few blokes with wheelbarrows

If you really want to mix yourself, hire a cement mixer but still get a friend with a wheelbarrow to help

If you're going to do it solo, buy a tube of radox to put in the bath afterwards

Given the temperature in the coming months, you may want to add an accelerator to the mix

I wouldn't bother with reinforcement, will only make it a real bitch to take up in 15 years time. If you're worried about cracking add fibres instead.

[dmahon]

Alternatively, just put it on decking. Ideally with a small concrete block in the middle with a pier bolted to it. Cheaper and easier.

[dmahon]

As to cost - £200 for the concrete plus formers and a days labour for a builder and his mate to dig and pour. Add £50 to hire a mixer/whacker and another £50 for hardcore. If they have a mini JCB, half a day but add £100 for the machine hire.

But I bet they quote you a couple of thousand.

[George]

Alternatively, just put it on decking. Ideally with a small concrete block in the middle with a pier bolted to it. Cheaper and easier.

More than adequate

POD's weigh next to nothing so anything more than decking is overkill and going to be a unnecessary cost. 3 pads can be cast for the pier legs far more cheaply than than one big pad for the POD.