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Should I be concerned about Honeycomb in Pier?

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#1 Bry

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Posted 02 July 2020 - 09:01 AM

Hello!

 

I just poured a concrete post for my SkyShed pier.  Yesterday, I removed the sonotube form and discovered a considerable amount of 'honeycomb' around the post. 

 

When mixing the concrete, I erred on the side of not over watering to ensure a stronger bond.  But, of course, that also means the concrete was less fluid and more prone to honeycomb.  I had attempted to use an electric sander as a vibrator to help consolidate the concrete, but obviously it wasn't very effective.

 

Here are some pictures.  It looks ugly, for sure, but I'm more concerned about the structural integrity.  

 

Should I be concerned about the structural soundness of this post?

 

Clear skies,

-Bry

 

Attached Thumbnails

  • Honeycomb1.jpg
  • Honeycomb2.jpg
  • Honeycomb3.jpg


#2 lee14

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Posted 02 July 2020 - 09:18 AM

I seriously doubt there's a structural issue. Tapping the surface with a hammer would reveal any extensive interior cracks. It looks pretty massive, may 8 - 10 inches?  If the surface appearance bothers you, you could skim coat it with an application or two of mortar, or even 'Quickwall', which is high strength mortar combined with fiberglas.

 

Lee


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#3 AstroBrett

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Posted 02 July 2020 - 09:24 AM

Do you have longitudinal rebar along the length of the pier?  Concrete is very strong in compression, but has little strength in tension.  The purpose of re-bar is to provide strength in tension so the composite material is strong under both regimes.  Any off-center load will introduce flexure, where one side on the pier will be in compression and the other side will be in tension. As an example, the center of mass of a wedge-mounted SCT will be off-axis with respect to the pier, and will introduce a considerable torque and flexure, while the center of mass of a counterweighted equatorial mount will generally be close to the centerline of the pier and will not. In the former case, one side of the pier will be under tension, while in the latter the entire pier will be under compression.

 

If you are mostly loading the pier in compression, I don't think the honeycomb will matter. If your setup will induce tension in the pier, and the concrete is unreinforced, it might be a problem. 

 

I hope that helps.

 

Brett     


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#4 Bry

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Posted 02 July 2020 - 09:47 AM

...It looks pretty massive, may 8 - 10 inches?  ...

 

Lee

Thanks, Lee!  Very helpful.  The post is 16'' in diameter.  I used a 48'' length sonotube.  A little over 39'' of the tube is above grade.  I dug another 24'' below grade (live in California with negligible frostline issues).

 

Do you have longitudinal rebar along the length of the pier?  Concrete is very strong in compression, but has little strength in tension.  The purpose of re-bar is to provide strength in tension so the composite material is strong under both regimes.  Any off-center load will introduce flexure, where one side on the pier will be in compression and the other side will be in tension. As an example, the center of mass of a wedge-mounted SCT will be off-axis with respect to the pier, and will introduce a considerable torque and flexure, while the center of mass of a counterweighted equatorial mount will generally be close to the centerline of the pier and will not. In the former case, one side of the pier will be under tension, while in the latter the entire pier will be under compression.

 

If you are mostly loading the pier in compression, I don't think the honeycomb will matter. If your setup will induce tension in the pier, and the concrete is unreinforced, it might be a problem. 

 

I hope that helps.

 

Brett     

Thanks, Brett!  Yes - I did include rebar along the length of the pier, so I should be good from that perspective.  Plus, I use an EQ mount, primarily with a 132mm refractor, so the center mass should be more compression than tension in my case.

 

Again - thank you all for the quick replies!  I'm resting a little easier now...

 

-Bryant


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#5 MikeTahtib

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Posted 02 July 2020 - 09:51 AM

I wonder if it was poured too dry if the cement is strong enough.  Cement doesn't dry, but hardens, and needs enough water to create the correct chemical composition.  Is it powdery or flakey?



#6 petert913

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Posted 02 July 2020 - 10:02 AM

It ain't goin' anywhere  :)



#7 macdonjh

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Posted 02 July 2020 - 11:16 AM

Honeycomb on the surface is unlikely to affect anything.  However, if you made your mix really dry, or didn't vibrate or compact the concrete as you filled your Sonotube you may have voids in the interior of the mass.  That can affect the overall strength of your pier.  Even so, it's unlikely to be harmful to your installation.  Even loading your 16" diameter pier with a couple of hundred pounds of gear will only be a small fraction of what it can support.  Even if that load is horribly unbalanced.

 

If you don't like the look of the honeycomb, get some mortar, make a fairly wet mix and apply it as a skim coat to cover the voids.  You can also buy a rubbing stone to smooth the mortar surface after it begins to harden.


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#8 Lola Bruce

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Posted 02 July 2020 - 11:30 AM

Wrap it with canvas or something you can keep wet for a day. Goal is to kick of any dry cement. After a while for cure give it a thunk to see if it's solid.

 

I think it would look good wrapped in small river rock pebbles.

 

Bruce


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#9 SonnyE

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Posted 02 July 2020 - 11:35 AM

If anybody asks, just tell them, "Yeah, I designed to look that way. Ain't it kool?"


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#10 Carl N

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Posted 02 July 2020 - 12:20 PM

Could even coat with garage floor epoxy in a neat multicolor. Would look good in that honeycomb surface.
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#11 OldManSky

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Posted 02 July 2020 - 01:58 PM

Wrap it with canvas or something you can keep wet for a day. Goal is to kick of any dry cement. After a while for cure give it a thunk to see if it's solid.

 

I think it would look good wrapped in small river rock pebbles.

 

Bruce

That.  Keep it wet during curing.  That won't reduce the honeycomb, but it will insure that all of the dry cement reacts properly and hardens well.

If the look bothers you, wait for it to cure then put a layer of mortar on the outside, troweling it smooth.  Coat the whole thing with concrete sealant after it's fully cured, and paint it :)


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#12 123456

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Posted 24 July 2020 - 10:57 PM

Just get a 10 lb bag of sand grout
Like you would use with tile
And get the rubber towel
Mix it wet.
And smear it on Lots of colors


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