Pouring concrete footings is an important first step in building any structure. Properly poured footings provide a stable foundation to support the weight of the walls, floors, roof, and anything else built on top. While pouring concrete can seem intimidating, it simply requires careful planning, the right tools, and step-by-step execution. Here is a complete guide to successfully pouring concrete footings for your project.
Choose the Right Concrete Mix
The first step is selecting the right type of concrete. For most residential footings, a mix of 1 part cement, 2 parts sand, and 3 parts gravel aggregate is sufficient. This is generally a 3000 psi mix. However, for heavy structures like multi-story homes, commercial buildings, or structures in areas with poor soil, a stronger 3500-4000 psi mix may be required. You can buy premixed concrete or mix it yourself.
Considerations for Mix
- Strength: Footings need a dense, durable concrete to prevent cracking under load. Aim for at least 3000 psi.
- Workability: The mix should be wet enough to flow into the forms, but not soupy. A slump test of 3-5 inches is ideal.
- Aggregate size: Use a maximum 3/4 inch crushed stone. Larger stones can leave voids.
- Entrained air: Air entrainment improves workability and freeze-thaw resistance. Most bagged mixes include it.
- Reinforcement: Steel rebar adds tensile strength. Use #4 or #5 bars, spaced 8-12 inches apart.
Calculate Concrete Volume
Before mixing and ordering concrete, calculate the total volume you will need in cubic feet. Measure the length, width, and depth of each footing area. Multiply together for total volume, then add 10% more for spillage and overages. Having too little concrete partway through a pour can ruin the job.
Set Up Forms
Forms create the outer structure to hold the concrete until it hardens. Use 2×4 or 2×6 lumber to build forms 2-4 inches wider than the footer dimensions. Drive stakes outside the forms to hold them in place. Consider key form requirements:
- Forms must be level across the tops. Use a transit or laser level.
- Seal form joints with caulk so concrete doesn’t leak
- Coat inside of forms with release agent so concrete doesn’t stick
- Brace forms well so they don’t bow under concrete weight
- Set form height for footing thickness required by code or plans
Add Steel Reinforcement
Once forms are built, cut and place steel rebar inside according to code or engineering requirements. Steel reinforcement strengthens the concrete to prevent cracking under structural loads. Key rebar considerations:
- Place bars 2-3 inches from bottom and sides of footing
- Overlap bars at joints by 40 bar diameters
- Tie bars together with wire to hold in place
- Stand bars on chairs or blocks for proper spacing
- Observe required spacing between bars (usually 8-12 inches)
Order and Transport Concrete
Call your selected concrete supplier about 1 week before your planned pour. Confirm your ordered cubic yards and specify your mix design, slump, and any special conditions like pumping. Choose a provider with mixing trucks to deliver fresh, quality concrete throughout the pour.
On the day of the pour:
- Give 24 hour notice for concrete delivery time
- Check forecast and reschedule if rain is expected
- Clear a path for the truck to access the pouring area
- Have tools and forms ready before concrete arrives
Prepare for the Pour
Just before the concrete truck arrives, follow these steps:
- Wet down forms to prevent absorption of water from concrete
- Double check form alignment, bracing, and rebar setup
- Stage tools like shovels, come-alongs, and floats nearby
- Remove debris from foundation area
- Designate spaces to washout tools and prohibit trucks
When the truck arrives:
- Direct it into position near pour area
- Confirm concrete specifications match your order
- Insert slump cone for driver to check consistency
Start Placing Concrete
With forms prepped and concrete ready, you can begin carefully placing it into the footings:
- Pour in lifts: Fill forms 6-12 inches at a time to avoid aggregate separation
- Vibrate or tap: Use a concrete vibrator or tap forms with hammer to settle concrete
- Maintain 2-3 inch clearance around rebar to avoid honeycombing
- Don’t overwork: Excessive vibrating or tamping results in weak spots
- Check form alignment periodically and adjust bracing
- Order loads timed so concrete always stays plastic
- Avoid cold joints: New loads should blend into still-plastic previous loads
Strike Off and Finish Concrete
As you fill the forms, use a straight 2×4 lumber “screed” to strike off the excess concrete flush with the top edge of the forms. This creates a flat, level surface. Additional finishing creates a smooth top:
- Bullfloat the surface to embed large aggregates just after strikeoff
- Darby back and forth to flatten and smooth the surface
- Float lightly to fill minor voids and depressions
- Edge the perimeter with an edging tool for a clean finish
Do not overwork the surface, as this weakens the concrete. The footing top surface does not need to be polished smooth.
Cure and Protect Concrete
Fresh concrete must be protected as it cures for several days. Premature drying leads to weak spots and cracking. Follow these curing steps:
- Cover surface with curing compound or plastic sheeting
- Keep concrete moist for 3-7 days, misting as needed
- Do not allow vehicles, materials, or equipment on footings for at least a week
- Avoid freezing temperatures for the first 24 hours or damage can occur
- Forms can usually be removed after 2-3 days if concrete is hard
With proper curing, concrete footings gain strength over 28 days to fully support the structure. Now you’re ready to build on top!
Frequently Asked Questions About Pouring Concrete Footings
Here are answers to some common questions about pouring concrete footings correctly:
How deep should concrete footings be?
Footing depth depends on frost line, soil conditions, and load. As a rule, go down to solid bearing about 12 inches below frost line. Heavy structures may need deeper footings.
What size rebar for footings?
Use #4 or #5 rebar, spaced 8-12 inches apart. Go with larger #5 bars for heavy loads. Place bars 2-3 inches from footing bottom and sides.
How much gravel under concrete footing?
Spread 4-6 inches of gravel fill under footings for drainage and stability. Compact it thoroughly before pouring.
Can it rain on fresh concrete footings?
Avoid pouring right before rain. If caught off guard, cover concrete with plastic sheeting, move forms tight together, and mist cure the surface.
How long do I wait to build on concrete footings?
Let concrete cure for at least 7 days before building. Wait 3-4 weeks to fully reach design strength. Test cylinder samples can verify if gain strength properly.
What is the ratio for 3000 psi concrete?
A typical 3000 psi mix is 1 part cement, 2 parts sand, and 3 parts aggregate gravle or crushed stone by volume. Add just enough water for 3-5 inch slump.
Should footing concrete be vibrated?
Proper vibration removes air pockets and settles concrete fully around rebar. Under vibration leaves voids. Overdoing it segregates the mix. Vibrate just until concrete is consolidated.
How do you screed concrete footings?
Use a straight, clean 2×4 lumber piece. Rest it on side forms and drag back and forth, sawing off excess concrete. Move across entire surface to leave flat, level surface.
Conclusion
Pouring concrete footings provides a solid base for any building project. With good planning, proper tools, and attention to detail throughout the pouring process, you can achieve strong, durable footings that provide long-lasting support. Protecting and curing the concrete fully allows it to gain strength over the first month after pouring. Observe local building codes for specific footing requirements. With care and patience, even first-timers can successfully tackle this foundation project. The finished footings will provide peace of mind that the structure above rests on a stable base.