I have poured 11 piers + footings for my deck. In each I placed a J-bolt in the center to attach my adjustable post base to. Despite my best efforts some of the tops of the piers aren't perfectly level meaning our post would not be perfectly plumb.

How can I resolve this issue? I've seem/been told there are several options.

  1. Grind the pier with a grinder to make it level
    • pros: fix the issue at the source, maximum area of contact from pier to base
    • cons: not sure how to ensure levelness, dust, could remove too much material
  2. Place shims between the concrete pier and the adjustable post base
    • pros: inexpensive
    • cons: reduces contact area between pier and base, durability
  3. Apply some concrete patching to level out the tops
    • pros: ?
    • cons: durability concerns, unsure if it's adhere to top of pier
  4. Cut the 6x6 post at an angle to adjust for any non-level piers
    • pros: none I think!?
    • cons: getting exact angle will be difficult, creates patches on patches

I'm inclined to fix the issue at the source with a grinder. However, I'd like to know what others think. By no means am I an accomplished builder.

How would you solve this issue?

  • If you'd used a grinder, what can I ensure I get a nice level surface?
  • If you'd use shims, should they be plastic, composite, metal?
  • Advice from @popham is good, but how out-of-level are we talking, here? Would a washer under one side fix everything? Commented Sep 30, 2023 at 23:08
  • a washer might be sufficient but as with shims would there be concerns about weight distribution not be spread out over the full bottom of the base? Commented Oct 1, 2023 at 1:25

2 Answers 2


Buy some mortar and bed your post bases in the mortar when it's still workable. Use a level, of course. S type mortar that you'll commonly find at hardware stores is fine. You've got a surface area of 3-1/2" square, so the 1800 psi minimum bearing strength would get you 22000# of strength.

  • Embedding the post base in the mortar might defeat the purpose of the adjustable post base. I got adjustable ones as the bolts, while largely in a start line, aren't quite perfect, and I needed the additional leeway. Commented Sep 30, 2023 at 22:35
  • @Ryan Taylor, when do you intend on finalizing your post base positions? After the deck is sitting on them? I imagine that most people would buy adjustable to accommodate some variation in J bolt positioning, but the J bolts are set in concrete now. I think you should run out a string line and prescribe the final positions now.
    – popham
    Commented Sep 30, 2023 at 23:01
  • In terms of when... I was thinking I'd do so after the initial posts and beams were constructed, since the beam would be pretty straight. I thought that might help find the best alignments for the bases, then I would tighten them in place. Is that the last responsible moment? I am concerned about making an unrecoverable error. Commented Oct 1, 2023 at 1:24
  • Ryan Taylor, if you level your foundations by bedding a piece of galvanized sheet metal, say, instead of the post base, then you can move those bases years after the deck is complete. If the base is out of level, however, then moving horizontally may also imply downhill and shift elevations on you. You can fix that change in elevation by wedging the base up and filling below the spacer with hydraulic cement, but all of this complexity seems crazy.
    – popham
    Commented Oct 1, 2023 at 1:36
  • Ryan Taylor, I'll always make a CAD drawing of work like that. It reduces my error rate greatly. There's a free program called LibreCAD that is a halfway decent clone of AutoCAD LT, if you're interested. I'm on Linux, but I'm pretty sure that they distribute a Windows version too. And technically you could tear off those post spacers if they were bedded in mortar at the wrong location. In construction the only "unrecoverable" errors are causes of death.
    – popham
    Commented Oct 1, 2023 at 1:38

I upvoted the @popham answer, but wanted to note that grinding isn’t the devil you appear to think it is.

Buy a diamond cup wheel and a mask. Remaining dust isn’t an issue because you’re outdoors. Level is set with a level. You won’t grind too much, and even if you did, you’d just go to the other side.

While perfect is, well, perfect, getting to 1/8" over a foot is pretty darn good.

  • 1
    I mean, if a washer is sufficient to level it, it should be well within the range of a little griding.
    – Huesmann
    Commented Oct 1, 2023 at 12:56
  • 1
    This is the approach I am going to take. Once complete, pending success, I'll accept this answer. I will move slow and methodical. I like that this solves the problem at the root and will provide maximum surface area for the post base connector to concrete pier. Commented Oct 3, 2023 at 12:47
  • I've begun grinding away at the first pier and it's a lot better than it was. As best as I can tell with my level I only have a pitch of 1/8". If I understand that right, that's 1/8" slope over 1 ft. How level is level? Should I grind away that pesky 1/8"? Commented Oct 6, 2023 at 17:18

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