Pour Concrete Footings
Fill holes with concrete using cardboard tube forms. Use 3000 PSI concrete and set post anchors while the concrete is still wet for a solid foundation.
Quick Summary
3-4 hours
Moderate
3000 PSI minimum
48-72 hours
Why Proper Footings Matter
The Foundation of Your Deck
Footings are literally the foundation of your entire deck. Every pound of weight - the lumber, furniture, people, and snow loads - transfers through the posts to these footings. Improperly poured footings can sink, crack, or heave, causing your deck to become unstable or unlevel over time. This is not a step to rush.
Concrete footings serve several critical functions: they spread the deck's weight over a larger area of soil, they anchor the posts to prevent lateral movement, and they extend below the frost line to prevent heaving during freeze-thaw cycles. Taking the time to pour them correctly now will save you from expensive repairs later.
Most deck failures and code violations stem from inadequate footings. Building inspectors pay close attention to footing depth, diameter, and concrete quality. Don't cut corners here - your deck's safety depends on solid footings.
Materials You'll Need
Concrete and Forms
- 3000 PSI concrete mix - Calculate about 0.6 cubic feet per 8" diameter x 12" depth
- Cardboard tube forms (Sonotubes) - 8", 10", or 12" diameter as specified by your plans
- Gravel - 4-6 inches for drainage base
- Post anchors/brackets - Galvanized or stainless steel
Tools Required
- Concrete mixer or large mixing tub
- Shovel and wheelbarrow
- Hand tamper or steel rod
- Level (4-foot and torpedo)
- Work gloves and safety glasses
Concrete Calculator Tip
For a 10" diameter tube that's 42" deep, you'll need about 0.8 bags (60 lb) of concrete per footing. Always buy 10-15% extra to account for waste and spillage. It's better to have extra than to run short mid-pour.
Step-by-Step Instructions
Prepare the Holes
Before pouring concrete, ensure your holes are properly prepared. Add 4-6 inches of gravel to the bottom of each hole - this provides drainage and prevents water from pooling under the footing. Tamp the gravel firmly with a hand tamper or the end of a 2x4 to create a stable, compacted base.
Set the Tube Forms
Cut your cardboard tube forms (Sonotubes) to length if needed. Place each tube in its hole, ensuring it extends 2-3 inches above grade level. This raised lip keeps moisture away from the post base. Use a level on top of the tube to ensure it's perfectly plumb.
Backfill around the outside of the tube with soil or gravel to hold it in position while you pour. Pack it firmly so the tube doesn't shift when you add concrete.
Mix the Concrete
Use 3000 PSI or higher concrete mix. Follow the package directions for water ratios - this is critical for proper strength. The ideal consistency is like thick oatmeal: wet enough to flow into the form but not soupy. Concrete that's too wet will be weak; too dry won't fill all the voids.
Mix only what you can pour in 15-20 minutes. Don't add extra water to concrete that's starting to set - this dramatically weakens the final product.
Pour the Concrete
Shovel or pour concrete into the tube form, filling about 6-8 inches at a time. After each layer, use a long stick, piece of rebar, or shovel handle to "rod" the concrete - push it up and down repeatedly to consolidate the mix and release trapped air pockets.
Continue adding layers and consolidating until the tube is filled to the top. Tap the outside of the tube with your hand or a hammer to help settle the concrete and release air bubbles near the edges.
Set Post Anchors
While the concrete is still wet (within 20-30 minutes of pouring), set your post anchors. Push the anchor into the center of the footing until the base plate is at or slightly below the concrete surface. Use a torpedo level to ensure it's perfectly plumb in both directions.
Double-check that the anchor is aligned with your layout strings - this is your last chance to adjust position. Once the concrete sets, moving an anchor requires demolishing the footing and starting over.
Allow Proper Curing
Concrete needs time and moisture to cure properly. Cover the footings with plastic sheeting or damp burlap for the first 48-72 hours. In hot weather, mist the concrete several times daily to prevent too-rapid drying, which causes cracking and weakness.
Wait at least 48 hours before attaching posts - 72 hours is better. For maximum strength, wait a full 7 days before putting significant loads on the footings. Concrete reaches about 70% of its strength at 7 days and full rated strength at 28 days.
Common Mistakes to Avoid
Adding Too Much Water
Soupy concrete is easier to pour but dramatically weaker. Every extra gallon of water per cubic yard reduces strength by about 200 PSI. Stick to the recommended water ratio even if mixing is harder.
Not Consolidating Properly
Skipping the rodding step leaves air pockets that weaken the footing. Those voids can fill with water, freeze, and crack the concrete. Take the time to consolidate each layer thoroughly.
Misaligned Post Anchors
Post anchors that are off-center or tilted create problems throughout the entire build. Posts won't be plumb, beams won't be level, and your deck will never look right. Check alignment multiple times before concrete sets.
Building Too Soon
Impatience is the enemy of strong footings. Putting loads on concrete before it's cured can cause micro-fractures that grow over time. Wait the full 48-72 hours minimum, longer in cold weather.
Weather Considerations
Hot Weather (Above 80F)
- - Pour in early morning or evening
- - Keep materials shaded before use
- - Use cold water for mixing
- - Work quickly - concrete sets faster
- - Mist footings frequently while curing
- - Cover with wet burlap and plastic
Cold Weather (Below 50F)
- - Never pour on frozen ground
- - Avoid if temps will drop below 40F within 24 hrs
- - Use fast-setting concrete mix
- - Insulate footings with blankets
- - Extend curing time significantly
- - Consider postponing if below freezing
Frequently Asked Questions
How deep should deck footings be?
Deck footings should extend below the frost line in your area, which ranges from 12 inches in southern states to 48+ inches in northern regions. Check your local building code for the exact depth requirement. Footings that don't reach below the frost line can heave during freeze-thaw cycles, causing your deck to become unlevel.
What PSI concrete should I use for deck footings?
Use 3000 PSI concrete for deck footings. This strength rating is sufficient for residential deck loads and is readily available at home improvement stores. For larger decks or areas with poor soil conditions, you may want to upgrade to 4000 PSI concrete for added strength.
How long should concrete footings cure before building?
Allow concrete footings to cure for at least 48-72 hours before attaching posts and continuing construction. For maximum strength, wait 7 days. Concrete reaches about 70% of its strength in 7 days and full strength at 28 days. Avoid putting heavy loads on fresh footings.
Can I pour deck footings in cold weather?
Avoid pouring concrete when temperatures are below 40F or when freezing is expected within 24 hours. Cold weather slows curing and can weaken the concrete. If you must pour in cold weather, use fast-setting concrete, insulate the footings with blankets, and never pour on frozen ground.