Concrete Pier base surround ??

[Craney]

Hello there,

The concrete from my 2x3x2 ft  pier base is going 'off' at the moment   ( gonna leave it about 36 hours ).    After removing the shuttering there will be a 3 inch gap around the block iteself.     ( BTW, this is stand alone pier  sunk into the garden patio and not part of an observatory ).

What is the general advice on filling  this 'space'   with regard to isolating the block and  ( soon to be attached ) pier   from vibration of the surrounding ground ??

Should it be left empty or  filled with large diameter pebbles etc ??    

I am planning to  surround the  base of the pier itself with these kind of  pebbles, for  aesthetics and drainage.

 

Any  nuggets of experience most welcome.

Cheers,

Sean.

[Saganite]

Hi Sean,

 

I too have a 'stand alone ' pier in my garden and I just put stone pebbles all around for speed and cheapness, however, that for me was a bad decision. My scope is a 5" f15 so the pier is pretty high, and at times I need my stepladder in place. The problem is ,a stepladder on pebbles is not a good idea. I have managed for a year, 18 months, but have now scraped them all away and I am in the process of putting an 8' diameter ring of slabs around it. Whether this becomes a problem itself from rising warm air, well I will have to see. I did consider putting grass around it  but cutting it would then be a faff because I have erected a curved trellis screen around the North and East directions to shield me from all light sources.

My Observatory is open plan and evolving...

 

[Craney]

Thanks @Saganite      Yes I had a few ponderings on how high the pier will actually end up.   I eventually decided to sink the 'top surface'  of the block about 25cm below the patio.   This means the pier -mount interface will about 80cm proud of the horizontal, which should be good for HEQ5 and EQ6 extensions and scopes from a 12" F4  cooling tower to my dinky new 140 Mak.

I think in light of your comment I may  close in the diameter of the circular pebble ornamentation.   One never knows just when I need to adjust the far end of a scope aimed at the zenith. and need the kitchen chair....although I don't think I will be going to an F15 refractor..... just yet.

[Saganite]

Probably a wise precaution. I have used scopes standing on stone, tarmac etc, and I cannot say I have noticed a problem but  I am committed now and will have to 'suck it and see'.

I don't see a problem in winter which is my main observing time with this scope.

[Astrokev]

Does the shuttering go all the way to the bottom of the block? If so - i’m not sure why you did this, as it’s easier and more effective to pour concrete in direct contact with the soil. It may also be difficult to remove. However, assuming you can get the shuttering out, I’d suggest back filling with concrete. If this is a faff, tightly packed earth is probably ok, as a block the size you state is unlikely to move!

If transmitted vibration is a concern, polystyrene may help?

[Gina]

The shuttering on my block/pier just went down to about an inch below ground level.  Just enough to hold it and stop the concrete running out.  Screwing held the wooden parts together.

[Astrokev]

Reading your post again I now realise that your question was more about insulating the block and pier from vibration (presumably meaning you moving about around the pier). Since I have an obsy, my pier is unaffected since the obsy floor is not in contact with the block. I’ve therefore got no direct experience for piers on a patio etc, however I know folks who have just bolted a steel pier to a much smaller block of concrete in the ground without any insulation at all. This has worked perfectly and has not affected imaging. I’m therefore of the opinion that the risks of gently moving around the pier are somewhat exaggerated. That said, I wouldn’t advocate jumping up and down, or bashing the pier itself!

[Craney]

8 hours ago, Astrokev said:

Does the shuttering go all the way to the bottom of the block?

About 2/3rds down.  I put shuttering in so that I could precisely place my bolt template.  The pier has no variation with regard to the PA pin, so I had to have a degree of confidence that everything was going to be more or less lined up when the  beast of a pier finally sinks onto the  stud ends.   I will post some pictures when it is complete.

Yes the question was about transmitting vibration from near to the pier.   I did not want to go through all this effort to create something that would be prone to nearby movement, like just bolting the pier to the concrete patio slabs.

 

Well , last night I went for it and put loose pebbles down the outside with some sharp sand.  Shuttering was a bit problematic to remove, but it did eventually yield.

Todays job is the patio surface and hopefully a useable pier.

[Hallingskies]

Decking?

[Craney]

2 minutes ago, Hallingskies said:

Decking?

Well. maybe not a total replacement for the whole patio, but possibly a  small 'step' that  surrounds the pier.  This  would act as an aid in aligning etc  especially with the big Newtonians I have ,  and also provide a no-go area when taking exposures.

 

[Hallingskies]

That’s the idea, just to act as a bridge and stop you treading on the pier block really.  At my last house I did something similar.  I also put some tiny battery operated leds on the corners so I knew where I was in the dark!

[Astrokev]

14 hours ago, Craney said:

About 2/3rds down.  I put shuttering in so that I could precisely place my bolt template.  The pier has no variation with regard to the PA pin, so I had to have a degree of confidence that everything was going to be more or less lined up when the  beast of a pier finally sinks onto the  stud ends.   I will post some pictures when it is complete.

Yes some pictures would be good. I’m struggling a bit to understand your explanation above. 

[Craney]

On 04/05/2019 at 22:13, Astrokev said:

Yes some pictures would be good. I’m struggling a bit to understand your explanation above. 

I've uploaded some.    Job done, hopefully it will be OK.

Sean.