JoeD

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.

Wuzzat?

With this method there will be zero PSI on the concrete surface after it sets but this may be OK.

JoeD

I don't understand the comment about zero PSI on the concrete surface.

nealtw

I am sure MoreCowbell has done his concrete work by now and it looks perfect from my house.

Wuzzat?

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.

nealtw

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

notmrjohn

"...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.

__________________
[CENTER][FONT=Comic Sans MS]Measure twice, cut once.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]Look at the nail, not the hammer. Watch the fence, not the blade.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.[/FONT][/CENTER]

MoreCowbell

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.

notmrjohn

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?

__________________
[CENTER][FONT=Comic Sans MS]Measure twice, cut once.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]Look at the nail, not the hammer. Watch the fence, not the blade.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.[/FONT][/CENTER]

Wuzzat?

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.