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GlassWalker

Pier foundations

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I've just had an Altair Skyshed pier delivered. Also have possibly found a builder to do the foundations for me as I suspect I'm lazy enough it'll never happen if I DIY. The pier's webpage suggests a hole 3 ft deep and similar in size to the base plate template, which is a square of 40cm sides. Assume it'll get poured in one, and might be padded out with bigger lumps of rubble. Garden is a mess so I have flexibility in what goes down, but will probably go the route of decking around the pier.

So I'm wondering if I should stick to the 3ft x 40cm x 40cm block? Or if I might want something different? I'm primarily concerned about the ground shifting as it's a clay soil I'm in which is pretty good at holding water. How about going wider but shallower? Mount is an EQ6 and I'm sure my future scopes will only go up in weight, not down.

More generally, I don't have any plans for an observatory at this time, as due to my tiny enclosed garden the pier has to go pretty much in the middle of it to maximise the sky view. So my plan is to leave the mount fixed in place, polar align it well and forget. But it'll be outside in all weather, rain or shine. Would a posh bag be sufficient protection? I've seen one made of heat reflecting materials I can't find the link of at this time... but still I'm worried about possible heat, frost and condensation that might happen. Any tips?

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In regards to the foundation I wouldn't go shallower. I would also go wider but thats just me. Rather safe than sorry.

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The Sky at Night series of articles on a dome build suggested a main cube under the pier 3 foot in each dimension topped by a smaller one foot cube. I ended up with one a bit shallower as the contractor misunderstood the requirement.

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I take the renegade view that there is less need for giant pier foundations than is widely supposed. Yves' substantial Mesu Mount 200/ODK14 is freestanding on its own feet on a concrete floor around 4 inches thick in our obseratory. Images at 2.4 metres FL and with thirty minute subs show no issues of any kind. Sure, the land on which you place it will vary but I tend to be sceptical of the need for manic concreting.

YVES-M.jpg

M51-HaLRGB-22-Hrs-ODK14-V2-M.jpg

Monster concrete won't do any harm but we are not using three hundred ton scopes.

Olly

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Olly, you say it is "only" 4 inches thick, but how big an area is it? Way I see it, it has to resist turning. Long and thin, or thin and flat would probably do well there. Something a bit blockier might resist turning less well, but easier to lay without taking up a large area.

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A lot depends on the ground you're putting the foundation onto. Olly's place I suspect is a few inches above the bedrock, other obsys are built over clays or peaty soils which might shift if the ground became wetter or drier (my fathers house on clay subsided in a dry summer as the clay shrank). Climate also plays a part- the 'massive concrete block' pier theory originates from the States where the Continental Climate means winters are much colder and 'frost ground heave' might occur, unlikely in lowland UK though.

My own obsy pier is concreted to the bedrock which was only 18" down. But I have also sucessfully imaged from a tripod on a slab patio with no issues.

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Find out about your ground conditions.

Find out about your ground conditions.

Did I mention Find out about your ground conditions.

Check for services running across the location there could be water, gas or sewage pipes down there and I dont mean your own dometstic supplies. There are companies that will do this for you check the net and its always good information to have about your property in any case.

Put down a small pile of sand for a week and look at it from the house are you sure thats were its going. Concrete is a [removed word] to get out of the ground !!!

Think about the finish square sides and a nice smooth top it not difficult and worth the effort. Shuttering and floating it looks good and it will provide a good contact for the pier this isnt difficult.

Nothing worse to look at than bumpy lumpy concrete.

plan to take a week off afterwards either to stay up late and enjoy your new pier or lie in bed with a bad back !

K.

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I've agreed in principle with a builder to do it, so it'll be his back not mine! I've done my back in possibly from other work anyway... plan is to have the top nicely boarded into a square shape (is that shuttering?), about level with the ground so it'll not be too hard to hide in future if it should ever be necessary. And I'll (eventually) cover the area with decking anyway.

As for late viewing, that'll be more down to the weather! That reminds me, I need to order some more bits to go with this... always the way!

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So I'm wondering if I should stick to the 3ft x 40cm x 40cm block? Or if I might want something different? I'm primarily concerned about the ground shifting as it's a clay soil

Personally, I don't thinkk there's any merit to over-engineering something like this. You're not going to put a massive load (like a building) on top of the concrete-work, so it's load-bearing properties are largely irrelevant. At worst, you'll have about 1 person's weight on the foundations and a person can easily stand on an unsupported paving slab without it sinking, shifting, cracking or any other bad thing happening to it.

As for the ground shifting; I doubt it would happen and even if it did, so what? The worst possible scenario is that you'd have to re-do your polar alignment ever so slightly. It's not as if you'd end up with the Leaning Tower of Swindon. :laugh:

Also, don't forget about the future. It's unlikely that you'll want THAT pier in THAT location for all time (or that the people you eventually sell the house to would want it at all). So I'd suggest 2 things:

First, make the shape thicker at the bottom, so it's keyed into the ground

Second, have the top of the concrete a few inches below ground level. That way it'll be easy to cover over the pier with earth / grass when it's time to say goodbye to it.

Edited by pete_l

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Done 2 pier bases for my PierTech pier, both were 3ft in depth and 18" square. Both sites had decent soil, no clay. No issues on the first in 2 years, second one is only a couple of weeks old so early days yet.

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Would a posh bag be sufficient protection? I've seen one made of heat reflecting materials I can't find the link of at this time... but still I'm worried about possible heat, frost and condensation that might happen. Any tips?

is this what you were looking for

http://www.widescreen-centre.co.uk/Catalogue/365%20Series%20Covers.html

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On the pier, as said already I've gone for the guidelines on the Altair Astro page. The top will be easily hidden by decking if I ever decide to remove it.

The cover, the telegizmos covers are what I'm looking at, although I've not quite hit the order button yet while I work out what size to go for.

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If you have got clay soils they can shrink in hot weather and swell in the wet. A simple test if the clay is shrinkable is get hold of a lump and roll it in your hands if it resembles plasticine and stays in a firm ball then it's likely to be shinkable clay. If it is, then the rule of thumb for a foundation is to go down a mimimum of 1m to get out of th shrinkable zone in the UK. if you do decide to go shallower make sure you leave plenty of flexibility to re-level the pier should the foundation move.

A member NLO told me his pier is now un-useable as he did not dig a deep enough foundation in clay soils, but it took several years of long hot summers!

At the end of the day if it is to be permenant you don't want to do it over again so do it right first time. But if we have summers like the last 2 you won't need to worry about shrinkage!!!!

If your clay is anything like it is here it's a bitch to dig out!

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if you do decide to go shallower make sure you leave plenty of flexibility to re-level the pier should the foundation move.
I thought we'd come to the conclusion that piers do NOT need to be level for G.E mounts? Just so long as you can re-do your polar alignment (and the thing won't fall over), any orientation is usable.

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The hole has been dug and filled with concrete. Actually the builder got carried away and went a bit deeper and wider than I originally requested, doing about 60x60x100+ compared to the requested 40x40x90. This was in order to make it easier to dig the hole, although he might not have been thinking it was easy when it came to hand mixing the concrete. He claims he hit rock at the bottom, so I might have more support than I thought.

Anyway, that's left alone to set now, and I just have to resist the temptation to have a look at it. The pier, when it eventually goes in place, doesn't need to be perfectly level as this one has an adjustable top plate.

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is this what you were looking for

http://www.widescree...ies Covers.html

I think these are great, Ive had mine for a couple of months now (the 365 type) for my c.925/NEQ6, early days but so far no problems at all.

They are expensive but I got my direct from the states...... AND saved myself a few quid.... Rip Off Britain or what ? !!

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For a covering system that seems to work very well have a look here: http://stargazerslounge.com/topic/122340-a-homemade-freestanding-pier/page__hl__%20freestanding%20%20pier__st__20 The upturned plastic bin does most of the work in protecting the mount, the covers just keep the water at bay. Hope it gives you some ideas.

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Hi GlassWalker

Is your pier now in place and up and running.

Only I'm looking at the Altair Astro myself and would welcome your opinion.

Thanks

Mike

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It's partially set up. Enough to use, but not a final install. When I stop being lazy I want to level the pier a bit more. This isn't essential as you can correct for it on the top plate, but cosmetically I have a slight lean I want to tune out. It does pretty much what you expect it to. The only detail I overlooked myself is its height. When set up, it is quite a bit lower than the tripod that comes with the EQ6, so I find it uncomfortable to use visually. I did get the Skywatcher EQ6 extension separately to help with that, but that slips around too much so I can't use that without some physical modification I need to decide on at some point, perhaps next summer when days are long again.

On the installation, my smart idea of having the concrete base slightly below ground level might not be the wisest either, as I'm finding water collects there as the surrounding soil is saturated. The idea here is that in future if I want to move house it'll be easy to hide the base.

Also I'm finding the moisture I'm getting under the telegizmos cover is reducing. I have a theory on this... the sand I used to fill the pier may not be completely dry, so it is evaporating into the cover before condensing. Over time I hope it'll dry out then this'll stop happening.

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I think these are great, Ive had mine for a couple of months now (the 365 type) for my c.925/NEQ6, early days but so far no problems at all.

They are expensive but I got my direct from the states...... AND saved myself a few quid.... Rip Off Britain or what ? !!

Or get one of these

http://www.poundland.co.uk/product-range/a-z/chair-cover/

my EQ6 has been sat outside under one for a couple of months. No water ingress so far.

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