Concrete Footings: Preparing for the Pour

Today we are ready to begin pouring concrete for our building addition.  After a day or so of digging up the ditch for the footings, Tom and crew do last minute prep work.

Tom checks the ditches where the footings will be poured.  The dirt should be compact and clear of vegetation.  If  grass or weeds are left in the ditch they could rot and cause the footing to settle.  Over digging the ditch should be avoided so that the crew does not have to throw uncompounded dirt in at the last minute.

Concrete is strong in compression and weak in tension.  Rebar is needed to help even out the properties of concrete.  Rebar is a type of steel rod that is barbed or ribbed.  Rebar creates tension strength in the concrete.  The top of a footing is normally under compression.  Any concrete below the center of the footing is under tension. 

Since all concrete will crack at a certain point, the rebar acts as a balance to help distribute the qualities of concrete after it dries.  The rebar helps hold cracked concrete together.  The weight on top of the concrete will force the top edge of the footing together to prevent bending because it is pulling against the rebar.

Higher areas of load bearing should have bigger footings.  A bigger footprint in the dirt allows for a heavier walls to be poured.

Rebar should be set up in the footing ditch and tied together so that it does not rest on the ground.  The rebar should be surrounded by concrete at two inch spacings all around.  Burning rebar happens when the rebar doesn’t get covered fully by the concrete and water seeps in alongside the rebar and rusts the rebar.  Lap joints should be set up at nineteen rod diameters. 

Rebar should be firmly tied to keep it in place when wet concrete is applied. 

It might be a good idea to wet the ditch down with a garden hose.  If  the dirt is too dry during the concrete pour, moisture will get pulled out of the concrete and cause the outside circumference of the concrete to dry out quicker than the inside.  Water will get wicked out of the concrete in a dry or sandy soil.  The inside of the concrete is left to cure at a slower rate and cause a plastic shrinkage crack.