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Old 10-18-2012, 08:29 AM  
JoeD
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Originally Posted by MoreCowbell View Post
I am doing a project that involves pouring new concrete footings for several steel columns in my basement. I want as good a bearing surface between the concrete and the column base plate that I can get, which is why I am trying to think through how I will get the footing surface as level as I can get it.

If you are that concerned about the contact patch between the post and the footing then I would pour the footing and let the the concrete start to set up. Before it is solid place the post on the pad and level it. The concrete will be a perfect fit the bottom plate of the post. If you mix the concrete dry enough you could probably place the post right away.


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Old 10-19-2012, 11:17 AM  
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If you are that concerned about the contact patch between the post and the footing then I would pour the footing and let the the concrete start to set up. Before it is solid place the post on the pad and level it. The concrete will be a perfect fit the bottom plate of the post. If you mix the concrete dry enough you could probably place the post right away.
With this method there will be zero PSI on the concrete surface after it sets but this may be OK.


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Old 10-19-2012, 01:41 PM  
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I don't understand the comment about zero PSI on the concrete surface.

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Old 10-19-2012, 04:04 PM  
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I am sure MoreCowbell has done his concrete work by now and it looks perfect from my house.

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Old 10-19-2012, 04:13 PM  
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I don't understand the comment about zero PSI on the concrete surface.
Uncured concrete cannot support weight since it is a semi-liquid so
-unless concrete expands while curing (and it very well may)-
the surface of the concrete will just barely be in contact with the undersurface of the materials above it, so no pressure will be on the cured concrete surface.

If you drive a wedge between the cured concrete and the material it is supporting, that wedge may be seeing hundreds of pounds of compressive force, depending on how thick it is and how "elastic" the structure of the building is.

At least that is how I imagine it.
Strain gages can confirm or deny this idea and that's a bit beyond DIY stuff.
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Old 10-19-2012, 04:53 PM  
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You haven't concedured the weight of the post on the wet concrete.
http://www.orbitalfasteners.co.uk/en/products/no1-steel-metal-horseshoe-trouser-shim-galvanised-50x50x3mm

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Old 10-20-2012, 09:00 AM  
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"...MoreCowbell has done his concrete work by now"

I dunno, neal, he may still be drawing lines on the walls and flipping his level around
to get it accurate to the millimeter.

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Old 11-12-2012, 08:38 PM  
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Quote:
Originally Posted by JoeD View Post
If you are that concerned about the contact patch between the post and the footing then I would pour the footing and let the the concrete start to set up. Before it is solid place the post on the pad and level it. The concrete will be a perfect fit the bottom plate of the post. If you mix the concrete dry enough you could probably place the post right away.
I sort of ended up doing just what you described. I hung the column from above about 1/2" above the finished height of the footing surface and wrapped the baseplate with plastic wrap. I then placed the concrete and let it stiffen up for a few hours so the L-bolts would stay in place then lowered the column enough to where it just barely pressed into the concrete. After the concrete cured I removed the plastic and bolted the column down. The pictures explain it better than I can. Thanks.
dsc_1591.jpgdsc_1592.jpg
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Old 11-13-2012, 08:06 AM  
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Concrete form has leveling legs I see. I did a similar deal with hidden ones on PT deck for my AC.

BTW, cowbell, did you ever check your level for accuracy?

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Old 11-13-2012, 04:03 PM  
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This
http://www.egamaster.com/en/component/egamaster/categorias/220/Measuring_And_Detection/Spirit_Levels
says 0.5 mm out of 1 m, 1 in 2000, 0.03 degrees, is high accuracy.



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