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My obs build * inside now kitted out*.

MikeD

By MikeD
in DIY Astronomer

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MikeD

MikeD

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Well I have made a start on my 8' x 8' roll off roof observatory build. :D

I moved the old 6' x 8' shed

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Cut a tree down that was in the footprint of the new 8'x8' shed :wicked:

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Dug a 3'x3'x3' hole for the plinth.

Took me a while to dig as after 3" of soil I had to dig through 30 odd inches of a 80/20 clay/flint mix

(the flint made it a real pain as they stopped the spade dead when I hit them) >:D

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To add to this as I decked my whole garden( hate mowing

:lol:) a few years ago, so had to remove the soil through the house as I have no rear access to my garden.

I bagged it up and took a total of around 58 bags (in 8 bag loads) to the dump

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Next job is to mix up a tonne of concrete and fill it back in. :roll:

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I have never mixed concrete before so any tips on mix ratio and method would be greatfully received.

Mike.

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Andrew*

Andrew*

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I have never mixed concrete before so any tips on mix ratio and method would be greatfully received.

I was told for C-20 (probably what you need): 1 concrete : 4 coarse sand : 2 fine sand : 0.55 water (this depends on the "slump". You might only need .45 water or as much as .65 water depending on the moisture in the sand - no idea how to calculate this...)

HTH

BTW, looking good going!!

Andrew

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centroid

centroid

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Off to a good start there Mike, and I guess you're a few pounds lighter after digging that hole, and carting all those bags of soil throug the house.

I have to agree with JV, in saying do you REALLY need a cubic yard of concrete to support your pier?

There is an awful lot of hype talked about pier bases, and just how big they need to be.

If your pier base, and observatory floor are all joined together as 'one', then maybe a bit of extra concrete thickness is called for. However, if they are isolated from one another, then you can afford to ease back on concrete.

My Pier base is an 18" cube of concrete, with a 12" cube on the bottom to act as a bit of 'key' against any potential sideways movement.

The has supported my pier, along with the 10" LX200GPS, and 'piggy-backed' ED80 for some considerable period, without any vibration problem or movement. It now supports the 12" LX200R with 'piggy-backed' ED80.

In your case, the hole is dug now, so you migjht as well fill it up as planned, but you could have saved yourself a fair bit of digging, bag carrying, and concrete.

If you are going to be using 3/4" aggregate in you concrete mix, then a ratio of 5:1 or even 6:1 of aggregate to cement, is what I would use.

Keep the 'piccies' coming, I do find it of great interest to see 'backyard' obsy's being built.

Dave

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MikeP

MikeP

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If you haven't already concluded it yourself, hire a mixer. Mixing that sort of volume and getting a good consistent mix each time is back-breaking.

Dave is right, 5:1 or 6:1 of coarse aggregate to cement is perfectly OK.

Mike

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MikeD

MikeD

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I thought i was over kill, but I read on cloudy nights that 36" was the way to go

I recommend a minimum 36 inch diameter plug. It can, of course, be 36 inches square, but most contractors have access to a 3-foot auger which reduces the hole digging operation to about a 15 minute job.

The plug depth must be down to, or deeper than, the frost line, or three feet deep, which ever is greater. Failure to adhere to this requirement will result in not just minor settling, but listing of the pier by 10 degrees or more from frost heaving! The frost line in your area is well known to local contractors and is a firm requirement in building codes. Look it up and make your plug deeper.

so I thought better to go too big instead of too small.

Thanks for the concrete info guys. :lol:

Mike.

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anthony

anthony

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Good progress Mike on something that is quite hard work.

Its certainly a big hole and it may be overkill, but I am also of the mind that these things you do only once, so where reasonable, over engineer each bit. (Mine is 3' cubed too, and the chap who made my pier raised his eyebrows a couple of times :lol:)

Keep the piccies coming

Anthony

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saturn5

saturn5

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I must admit 3ft cubed does seem a bit much,a ton of concrete,one things for sure is the pier wont move,when i get round to digging mine(next week or two,work permitting)i will be going for 2ft cubed max.not because i think 3ft cubed is overkill but i cant be bothered digging a hole that big.

Cloudy Nights is an American site so things are a bit different in certain places over there regarding frost,

As for digging below the frost line here,the amount of frost we get or have got over the last several years is minimal,even up here in the North of Jockland so there is no threat of a pier tilting 10 degrees or more from frost heaving.

If i did dig a hole that size i would use it to bury my light polluting neighbour :lol:

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Kaptain Klevtsov

Kaptain Klevtsov

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One way round doing loads of concrete mixing is to chuck loads of big rocks in the hole and glue them together with the concrete.

Take care with the mixer as it will try to take the shovel off you and kill somebody close by if you stick it too far in.

Great start though, that hole would have taken me months as I'm very lazy.

Kaptain Klevtsov

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CELESCOPE

CELESCOPE

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Nice one Mike looking good , mine,s no where near that thickness , ,but then again i,m not imaging from the Dome , but can jump up and down beside mine with no movement on the puter screen , anyway ,keep them images coming ,love to see it all come together

Rog

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MikeD

MikeD

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One way round doing loads of concrete mixing is to chuck loads of big rocks in the hole and glue them together with the concrete.

I still have all the bricks in the first image can I chuck them in?

Take care with the mixer as it will try to take the shovel off you and kill somebody close by if you stick it too far in.

Will do. :shock:

Mike.

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GordonCopestake

GordonCopestake

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Great start! Cloudy Nights is a great resource, but like all americans they like things bigger then they need to be...

But that being said, better to be too big than too small! Fill it with your bricks, rubble, tiles, anything solid like KK said. The mixer will cost you £30 and save you a broken back, but I wouldn't like to face my missus if I had to cart all that through the house!

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lunator

lunator

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Mike

When I put my base doen it was a realy mixed bag of bricks, stones, paving slabs I was amazed at how the mix came together once the concrete was added.

The line about the frost issue is quite important in the US but here inthe UK we don't have frost that are that bad...

I'm looking forward to seeing the pier in place.

Cheers

Ian

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centroid

centroid

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All 'in hand' then Mike :lol:

Chemical bonding does work very well indeed, so it will be nice and secure.

I already had my pier to-hand, so made a template to hold the bolts in position, and cast them into the concrete. Only one 'shot' to get it right though :D

Dave

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