In this video, This Old House general contractor Tom Silva shows how to dig and pour concrete supports.
1. Lay two long straight 2x4s on the deck, allowing them to extend out to the center of the two footing holes.
2. Hang a plumb bob from the end of one 2x4. Set a footing form in place directly below the plumb bob. Adjust the form until it's centered on the plumb bob.
3. Use a pointed shovel to scribe the dirt around the form.
4. Move the form out of the way and dig the footing hole down to the frost line or 4 feet deep.
5. Repeat Steps 2 through 4 to create the second footing hole.
6. Set the footing forms into the holes. Check that they're centered below the plumb bob, then backfill around the footing forms with dirt.
7. Set a fiber-form tube on top of each footing form. Measure 8 inches above the surrounding grade and make a mark onto each tube.
8. Cut the tubes to length with a circular saw.
9. Set the tubes on top of the footing forms and backfill with dirt. Again, use the plumb bob to ensure the tubes are centered.
10. Mix concrete in a wheelbarrow and then shovel the wet concrete into each hole, stopping about 12 inches from the tops of the fiber-form tubes.
11. Into each tube insert four ½-inch-diameter x 48-inch-long metal reinforcing bars.
12. Add more concrete to completely fill each fiber-form tube.
13. Tap the side of the tube with the shovel to release any trapped air.
14. Take a 1x2 and poke down into the tube several times to settle the concrete.
15. Use the 1x2 to screed off any excess concrete from the top of each tube.
16. Allow the concrete to cure for two days.