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How to secure deck beams to concrete blocks?

GreyWolf92 | Posted in General Questions on

Ilowes bought these concrete deck blocks from Lowe’s to build a deck.

I am putting ~1ft 4x4s on the blocks to raise off the ground.

Problem is, the space in the block is more for 4”x4” rather than 3.5” x 3.5”. Additionally it’s not completely flat inside the block… so it wiggles quite a bit. 

Am I supposed to pour concrete in these first to secure the post, or will it be enough just by the weight of the deck? Do I need a simpson post bracket before placing the beam (I thought the point of these were that post brackets are not needed)?

Thank you for your advice.

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  1. Expert Member

    Grey Wolf,

    Unfortunately they are sized for both nominal and actual sized 4"x4"s, which means they can be a bit sloppy. if you want a tight fit you may need to cut some 1/2" pt material and pad out the bottom.

    Remember those blocks are a really just a shortcut to provide some support for a deck. They don't provide any uplift protection of lateral support, and won't meet most codes. If you want any of those attributes you need to form and p0ur the footings yourself.

    More important than a connection to either the block or the beam is some bracing from the post to the structure above to keep the deck from simply toppling over. If it's that close to the ground some diagonal 4"x4"s secured with structural screws will probably suffice.

    1. GreyWolf92 | | #2

      Thanks for the info! Yea I decided I will just put some liquid nail on the bottom of them beam (connection to cement block).

      So basically the weight of the deck will hold these down and stable?

      1. Patrick_OSullivan | | #3

        You're saying beam, but I think you mean post.

        > So basically the weight of the deck will hold these down and stable?

        Impossible to say without understand the design of the deck. If the deck is free standing, only having posts on these blocks is likely going to be a pretty shaky structure unless it's cross braced well.

  2. PLIERS | | #4

    Liquid nails would potentially connect your post to the block better but stability would remain the same. I think it depends on how big your deck is. I would get a lot of concrete blocks and keep them close together. I’m not sure about distance between posts because don’t know how weather in your area is and how big the deck is. Either way having more blocks and posts would make your deck more stable and keep it from moving.

    1. Expert Member
      MALCOLM TAYLOR | | #5

      I don't think the spacing or number of blocks will make any difference to how stable the deck is. Only bracing or moment connections between the posts and beams above will do that.

      1. GreyWolf92 | | #6

        Thanks Malcolm. Can you explain a bit more in detail when/where the diagonal beams would go? Before or after the joists? If there is a diagram you can share, that would be great.

        Do you mean like this:

        Or like this:

        Deck is 6x24

        1. Expert Member
          MALCOLM TAYLOR | | #8

          Grey Wolf,

          Like the second link. The decking should keep everything fairly square. You just need something to keep it from falling over.

          On decks that close to the ground, I prefer to p0ur a footing with an integral pier up to the bottom of the beams. That deals with both vertical and horizontal loads so no bracing is necessary, and makes the framing a lot easier.

    2. GreyWolf92 | | #7

      Liquid nails helped with the wiggling. Yea you're right might not do much structurall but helps keep them stable when installing the beams.

      I also used composite shims.

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