Mailbox Under Construction
Notice that the masonry stones at the bottom of this mailbox column appear to decrease in size as they reach the rear of the column.
This is an optical illusion created by the fact that the concrete footing is level. (Notice that we carefully cut the lawn pad so that it will continue to grow around the base of the mailbox column when we have completed our work).
A LEVEL FOOTING helps counter any incline that might exist on your curbside parcel.
Column Mailbox Footings
Mailbox footings might just be the most important part of any column curbside mailbox. Although we don't want the footing showing under the column, neither do we want it to be so narrow or shallow that it doesn't hold during inclement weather.
But aesthetics isn't the only consideration. We take into account our local area's frost line, the type of soil we will be digging in, and whether the location is prone to drainage issues.
We see a lot of column mailboxes that, like this one, have been installed on a nearly non-existant concrete pad.
Although we don't have an appreciable frost line here in NE Texas, a substantial concrete pad is still important.
It helps carry the weight of the brick or stone
It provides a level surface on which to build
It counters water penetration that can lead to soil shifts during inclement weather.
Adjusting for Soil Types
After estimating the minimum depth of your concrete footing, the next step is to determine your type of soil. Clays, silt, and sand cannot bear the same amount of weight as "strong soils." This graph will help you understand the difficulties involved: (Please be advised that some soils have been deemed at 1000 lbs/sq foot. Err on the side of caution).
The depth of the concrete pad is determined by these factors:
1) The height of the column (Add 1" depth for every 3" in height).
2) The type of soil
3) Frost Line Depth (Dig 6" below frost line).
4) The rate of incline
5) Whether aggregate stones are required to facilitate drainage
6) The weight of building materials including cinder blocks, (if used).
How Deep should my Column Mailbox Footing Be?
Correcting for bad soil:
1) Do not backfill using excavated soils.
2) Compact the soil using a motorized compactor.
3) Introduce approximately four inches of 1.5 inch gravel into the base...(your hole must be excavated deeply enough to allow for this step).
4) Use transverse (crosswise) 1" or 2" rebar within the concrete form and at least one vertical piece of rebar in the center.
Correcting for poor drainage:
1) Press a layer of 2"-3" cobbles into the mud before building your concrete form.
2) If the issue is severe, you may want to insert a three inch pvc pipe angled toward the curb.
3) Be sure to pump out water prior to pouring concrete so that the base of the concrete footing does not weaken from absorbing excess moisture.
Correcting for inclines:
1) Remember that the back of the hole will appear deaper than the front in order for the footing to be level.
2) If you are using rebar, be sure to keep both the crosswise and vertical pieces level.
3) The streetside portion of the footing should meet ground level.
We have been building column mailboxes for more than two decades. We take considerable time making sure that our concrete footings are solidly built using all the analytical and/or power tools at our disposal. Our goal is that none of our clients ever have to experience a mailbox that resembles the Leaning Tower of Pizza.
If you are not the DIY type, please remember us. As always, we will put our expertise to work to help you devise a column mailbox you can be proud of for years to come.
Visit our Sister Sites:
Plano Column Mailbox Prerequisites
How long should a Column Mailbox Footing Cure?
It is our experience that if a footing is deeper than 4", it requires approximately 48 hours to cure. Even with today's "quick acting" cements, it is best to ensure this foundation is fully stabilized prior to adding any weight onto it.
Which is heavier - Brick or Stone?
Modern brick is an extremely dense product and therefore, certain porous stones are much lighter. (When calculating the potential weight of your column mailbox, don't forget to include cinder blocks if you use them for the interior framework).
What if I encounter a "Soft Spot" while Digging?
After determining how deep the soft spot is, it can usually be treated as if it were bad soil. Another option is to widen the entire footing, making sure to add sufficient rebar to ensure its strength.