Install Post Anchors
Set galvanized post bases in wet concrete while ensuring they're level and properly aligned. Adjustable post bases offer flexibility for fine-tuning post positions.
Quick Summary
10-15 minutes
Galvanized steel
Level + string lines
Alignment
Why Post Anchors Matter
The Critical Connection
Post anchors are the connection point between your concrete footings and your wooden posts. A poorly installed anchor means crooked posts, misaligned beams, and a deck that never quite looks right. Getting this step correct is essential for everything that follows.
Modern post anchors serve multiple purposes beyond simply connecting wood to concrete. Quality anchors elevate the post above the concrete surface, preventing direct contact with standing water and dramatically extending the life of your pressure-treated posts. They also allow for slight adjustments during installation and provide a solid mechanical connection that resists lateral forces.
The old method of embedding posts directly in concrete is now considered poor practice by most building codes. Concrete wicks moisture into the wood, accelerating rot from the inside out - often invisibly until the post fails. Post anchors solve this problem while making future post replacement much easier.
Types of Post Anchors
Embedded Post Anchors (Set in Wet Concrete)
Advantages
- - Strongest connection to concrete
- - No additional drilling required
- - Lower cost per anchor
- - Single installation step
Disadvantages
- - Must position perfectly while concrete is wet
- - No adjustment after concrete sets
- - Requires precise timing
- - Mistakes require breaking out footings
Adjustable Post Bases (Bolted to Cured Concrete)
Advantages
- - Position can be adjusted before final tightening
- - Install after concrete fully cures
- - Easier to achieve perfect alignment
- - Better standoff height (1-2")
Disadvantages
- - Requires drilling into cured concrete
- - Additional hardware cost
- - Extra installation step
- - Slightly weaker than embedded (still very strong)
Recommendation for DIYers
Adjustable post bases are recommended for DIY deck builders. The ability to install them after concrete cures removes the time pressure, and the adjustment capability makes it much easier to achieve proper alignment. The small extra cost is worth the peace of mind.
Choosing the Right Anchors
Material Options
- Hot-dipped galvanized - Best value, excellent corrosion resistance for most applications
- Stainless steel - Required for coastal areas or ground contact, highest corrosion resistance
- Powder-coated - Decorative option, may require touch-up over time
Size Matching
- 4x4 posts - Use 4x4 post base (actual 3.5" x 3.5")
- 6x6 posts - Use 6x6 post base (actual 5.5" x 5.5")
- Load rating - Check manufacturer specs match your deck design loads
ACQ Treated Lumber Warning
Modern pressure-treated lumber uses ACQ (Alkaline Copper Quaternary) preservative, which is highly corrosive to standard galvanized hardware. Always use hot-dipped galvanized (G185 or better) or stainless steel post anchors with ACQ lumber. Electroplated zinc coatings are not sufficient.
Step-by-Step Installation
Re-establish Layout Lines
Before setting any anchors, re-establish your string lines from the ledger board to the batter boards. These lines define the exact centerline of your beam and show where each post should be located. If you removed the strings during concrete pouring, take time to set them up again precisely.
Measure the diagonals from each corner of your layout to verify it's square. The diagonal measurements should be equal. If they're off by more than 1/4", adjust your string lines before proceeding.
Mark Anchor Positions
Using a plumb bob hung from the string line intersection, mark the exact center point on each footing. This mark shows where the center of your post anchor should be positioned. Double-check by measuring from the ledger board to confirm distance is correct.
Position and Set the Anchor
For embedded anchors: While concrete is still workable (within 20-30 minutes of pour), push the anchor standoff or bolt pattern into the center of the footing. Push down until the base plate is at or slightly below the concrete surface.
For adjustable bases: Center the anchor plate over your mark. Use the anchor as a template to mark bolt hole positions. Drill holes using a hammer drill and concrete bit (typically 1/2" for 3/8" anchors), clean holes thoroughly, insert concrete anchors, position the plate, and tighten bolts.
Check Plumb and Alignment
Use a torpedo level on two adjacent sides of the anchor bracket to ensure it's perfectly plumb (not tilted in any direction). An anchor that's even slightly tilted will result in a post that's visibly crooked.
Measure from the center of each anchor to your string lines. All anchors should be the same distance from the ledger. Also measure the spacing between adjacent anchors to confirm they're correctly positioned relative to each other.
Final Adjustments and Secure
Make any final position adjustments needed. For embedded anchors, this must happen while concrete is still workable - typically within 30-45 minutes of pouring. Use a small amount of concrete to fill any gaps around the anchor base.
For adjustable anchors on cured concrete, once alignment is verified, tighten all bolts to the manufacturer's specified torque. Don't over-tighten, which can crack the concrete or strip the anchor threads.
Common Mistakes to Avoid
Rushing Embedded Anchor Placement
Once concrete begins to set, you can't adjust anchor position. Take time to verify alignment before concrete becomes unworkable. It's better to mix concrete in smaller batches and set one anchor at a time than to rush and misalign them.
Ignoring Plumb
A tilted anchor means a tilted post, which cascades into problems with beams, joists, and decking. Check plumb in both directions (parallel and perpendicular to the house) for every anchor.
Wrong Anchor Size
A 6x6 post in a 4x4 anchor won't fit. A 4x4 post in a 6x6 anchor will be loose and unstable. Double-check your post dimensions against anchor specifications before purchasing.
Inadequate Corrosion Protection
Standard zinc-plated anchors will corrode quickly with ACQ-treated lumber. The anchor will fail long before the wood rots. Always use hot-dipped galvanized (G185 minimum) or stainless steel.
Working with Adjustable Post Bases
Why Adjustable Bases Are Worth the Extra Cost
Adjustable post bases cost $15-30 each compared to $8-15 for embedded anchors, but they offer significant advantages for DIY builders:
- Install after concrete fully cures - no time pressure
- Can reposition slightly if footing location is off
- Greater standoff height (1-2") keeps wood drier
- Easier future post replacement if needed
- Less stressful installation process overall
Installation Tips for Adjustable Bases
- - Wait at least 48-72 hours after pouring before drilling into concrete
- - Use a hammer drill with carbide-tipped concrete bit
- - Drill holes 1/4" deeper than anchor length
- - Clean dust from holes using compressed air or vacuum
- - Don't force concrete anchors - they should drop in easily
- - Tighten in a star pattern to ensure even pressure
Frequently Asked Questions
What type of post anchor should I use for a deck?
For most deck applications, use hot-dipped galvanized or stainless steel post anchors rated for your post size (typically 4x4 or 6x6). Adjustable post bases are recommended because they allow fine-tuning post position after concrete cures and keep the wood elevated above the concrete surface, preventing moisture damage.
How do I ensure post anchors are aligned?
Use string lines stretched from the ledger board to batter boards beyond the footings. All anchors should be the same distance from the ledger and equally spaced from each other. Measure from each anchor to the string lines and check diagonals to verify square before the concrete sets.
Can I adjust post anchors after concrete dries?
Embedded anchors cannot be adjusted after concrete cures - you would need to break out the footing and start over. Adjustable post bases bolted to cured concrete can be repositioned by drilling new holes, but this weakens the footing. This is why careful alignment before concrete sets is critical.
Do post anchors keep wood from rotting?
Quality post anchors elevate the wood post 1-2 inches above the concrete surface, preventing direct contact with standing water and improving air circulation. This significantly extends post life compared to posts embedded directly in concrete, which trap moisture and accelerate rot.