Announcement

Collapse
No announcement yet.

Concrete Deck Piers

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Concrete Deck Piers

    Hello,

    I am looking for some advice on the concrete piers I just poured for my deck.

    When I removed the cardboard from my piers I was expecting to see nice smooth concrete, but instead it is rough and filled with little voids. I used Quikrete concrete and mixed it in a wheelbarrow with measured amounts of water, etc., and was careful to tamp it down as I poured. The footings are a full 48" below grade, and I'm wondering if I should be concerned about the quality and longevity of my (first-time) concrete work.

    Would really appreciate any suggestions on what went wrong, and if there are any repairs or recommended fixes I need to do?

    Thanks in advance!
  • Thread Continues Below...

  • #2

    Re: Concrete Deck Piers

    The mix may have been too dry? Vibration rather than tamping would have helped.

    Put a parge coating on the exposed areas for appearances. The piers should be okay for many years.
    Egon
    from
    The South Shore, Nova Scotia

    Comment


    • #3

      Re: Concrete Deck Piers

      At the risk of sounding harsh you really shouldn't be taking the opinion of guys on the internet on potential structural issues.

      Is it a ground level deck or 2nd story deck?

      Did the building inspector approve the footings?

      Did you vibrate the footings when you were pouring them?
      Or tamp them down in any way?

      I vibrate my footings and use a piece of rebar in the middle of every sonotube.

      I would dig down around the worst looking ones and make sure they are solid throughout.
      Quikrete is not a great product for a finished look, it has large stones in it.

      Nathan
      Last edited by nnieman; 05-21-2020, 07:37 AM.
      Jerome likes this.

      Comment


      • #4

        Re: Concrete Deck Piers

        It does look like it might have been a bit on the dry side. I always get a stick and work it up and down in the tube where the exposed area is going to be to get the "cream" to flow to the outside. It is probably a better mix internally and I doubt if it will crumble and fail in your application. As was said, parging will make it pretty.
        billh
        MikeJunction likes this.

        Comment


        • #5

          Re: Concrete Deck Piers

          Originally posted by nnieman View Post
          At the risk of sounding harsh you really shouldn't be taking the opinion of guys on the internet on potential structural issues.

          Is it a ground level deck or 2nd story deck?

          Did the building inspector approve the footings?

          Did you vibrate the footings when you were pouring them?
          Or tamp them down in any way?

          I vibrate my footings and use a piece of rebar in the middle of every sonotube.

          I would dig down around the worst looking ones and make sure they are solid throughout.
          Quikrete is not a great product for a finished look, it has large stones in it.

          Nathan
          Concrete Piles:

          Engineered piles usually have a rebar cage installed. Size of rebar and number of rebar are dependant on design requirements. Spacing must also be in accordance to aggregate size as well as mandated side clearance. The post retainer also requires proper design involving holding power in. The concrete. There are very precise guidelines for vibration. Tamping could be used for non slump pours but those will not be common in sona tube pours.

          Soil conditions have to be evaluated for end bearing or friction piles. Digging down and looking will tell you little about the strength. Taking a core and analyzing it would be one way to go. But this would costly and it be more. Economical to just replace the pile.

          A few, very few of concrete pile design concepts.
          FD0504BB-5708-4FDF-BEDD-5BD9FE26C1DB.jpeg

          A piece of rebar down the center of a concrete pile is at the point of zero polar movement and does nothing for strength.
          Last edited by Egon; 05-21-2020, 08:36 AM.
          Egon
          from
          The South Shore, Nova Scotia

          Comment


          • #6

            Re: Concrete Deck Piers

            Originally posted by Egon View Post

            A piece of rebar down the center of a concrete pile is at the point of zero polar movement and does nothing for strength.
            Rebar down the center is not going to give the greatest strength, but to say it does nothing is just not correct.

            Comment

            • Thread Continues Below...

            • #7

              Re: Concrete Deck Piers

              Thanks everyone for your comments, I do appreciate it. As some have suggested, I think my mix might have been on the dry side, and probably needed heavier tamping. Was perhaps too cautious about making it too wet!

              It's a very small deck at 4'x4' (16 sq ft), and the underside of my 2'x8' framing is 24" above ground. Think I will take billh's and Egon's advice and parge it for appearances!

              Thanks again

              Comment


              • #8

                Re: Concrete Deck Piers

                Originally posted by drzaius View Post

                Rebar down the center is not going to give the greatest strength, but to say it does nothing is just not correct.

                Very true. It will add slightly to the compressive strength and if attached to the post anchor will aid in pull out strength. Most anchors will be designed for bending and side forces.
                Egon
                from
                The South Shore, Nova Scotia

                Comment


                • #9

                  Re: Concrete Deck Piers

                  I asked a planning engineer many years ago at my town hall about rebar in pier footings and he said unless the pier rises some feet above grade it is not required and it does nothing. He said it's all about compression below grade. As long as you don't have too dry a mix when pouring or a cold joint that could be an issue for frost heave reasons, don't bother wasting your money on rebar. So I was told.

                  I used my 18V Makita concrete vibrator for piers to avoid the honey comb look even though on the side of the Sonotube, it actually says 'Do not vibrate'. Go figure eh! Not sure why they have that warning. Maybe it is because it could cause the form to fail via maybe delaminating the cardboard of the Sonotube while still wet or that it could cause the form to shift place. Not sure, but it does say not to vibrate.

                  Parging it would mostly make them look prettier. Unless there are voids you have that are so deep that water can nest in crevices and subsequently freeze and cause the concrete to start breaking up, which is very unlikely they are that bad, I would just leave them alone.
                  Last edited by Lost in the Woods; 05-22-2020, 09:25 AM.
                  MikeJunction likes this.
                  Kevin

                  Comment


                  • #10

                    Re: Concrete Deck Piers

                    Originally posted by MikeJunction View Post
                    Thanks everyone for your comments, I do appreciate it. As some have suggested, I think my mix might have been on the dry side, and probably needed heavier tamping. Was perhaps too cautious about making it too wet!

                    It's a very small deck at 4'x4' (16 sq ft), and the underside of my 2'x8' framing is 24" above ground. Think I will take billh's and Egon's advice and parge it for appearances!

                    Thanks again
                    None of these notes defines your interpretation of "tamping." If you mean tapping/pounding (not "heavier tamping") on the surface that is an unworkable error. What should have been done is to emulate the mechanical vibration by aggressively "oscillating" up and down in a 3" or 4" stroke something as simple as a long 1" square stick in the mix, starting at the bottom as you gradually increase the pour, moving it upward with each ~4" added.

                    No mention is made of why they go as deep as 48" as to terrain, slope (?) or general soil condition - are they drilled in filled land for example? The left pic seems to show a steep slope.

                    The uniform voids across the full pour in the pic show it to be too dry.

                    Although unrelated to the mix, 8" framing for a 4' deck seems overkill. 6" would seem to be more than enough particularly is there are three joists across 48".
                    Start slow and wind down gracefully

                    Comment


                    • #11

                      Re: Concrete Deck Piers

                      "No mention is made of why they go as deep as 48" as to terrain, slope (?) or general soil condition - are they drilled in filled land for example? The left pic seems to show a steep slope."

                      Might be for something you probably never encounter. Frost. In my town the spec is ten feet to get below the frost line. I had helical/screw piles installed rather than try to make 10' deep holes for my deck.

                      Pete

                      Comment

                      • Thread Continues Below...

                      • #12

                        Re: Concrete Deck Piers

                        Originally posted by Woodwreck View Post

                        None of these notes defines your interpretation of "tamping." If you mean tapping/pounding (not "heavier tamping") on the surface that is an unworkable error. What should have been done is to emulate the mechanical vibration by aggressively "oscillating" up and down in a 3" or 4" stroke something as simple as a long 1" square stick in the mix, starting at the bottom as you gradually increase the pour, moving it upward with each ~4" added.

                        Although unrelated to the mix, 8" framing for a 4' deck seems overkill. 6" would seem to be more than enough particularly is there are three joists across 48".
                        Actually, your example of 'oscillating' describes what I did to a tee (including use of a 1" stick).

                        The 2x8 framing isn't required for the joists per se, but is required by local bylaw on the outside (rim) joists for attachment of 4x4 guardrail posts.

                        Comment


                        • #13

                          Re: Concrete Deck Piers

                          Originally posted by MikeJunction View Post

                          Actually, your example of 'oscillating' describes what I did to a tee (including use of a 1" stick).

                          The 2x8 framing isn't required for the joists per se, but is required by local bylaw on the outside (rim) joists for attachment of 4x4 guardrail posts.
                          Thank you for the joist clarification. Then that leaves two things. Presumably your slope appearing in the left pic explains 48" deep, but I don't take issue with that in itself.
                          I only comment in that 48"-worth of a lot of bags in a wheel barrow are really labor intensive and require more examination of the consistency of the mix.


                          Pete reminds me of an interesting point that i thank him for, in the tundra of Saskatoon. Not sure about Toronto*, but we have the likes of something similar in our cabin and homes in the Sierra Nevada toward Tahoe but which I clarified above:

                          Might be for something you probably never encounter. Frost. In my town the spec is ten feet to get below the frost line. I had helical/screw piles installed rather than try to make 10' deep holes for my deck.

                          Pete

                          * "In Northern Ontario it can get as cold as –50˚C, but the winter in Toronto is much milder. The temperature doesn't usually go below –20°C and the average winter temperature is only –4.6˚C." National Weather Service/Yahoo
                          Start slow and wind down gracefully

                          Comment


                          • #14

                            Re: Concrete Deck Piers

                            Your our concrete isn't consolidated. You simply didn't manage to get the voids out of the concrete.

                            You can consolidate concrete with a concrete vibrator or you can do it manually..... the way I do this is by rodding it (repeatedly plunging a wood or metal rod into the concrete to get rid of voids) then tapping the sides of the form with a hammer to get a good surface finish.

                            Concrete should be mixed as dry as possible while thoroughly hydrating the cement powder. The problem is that dry mix that makes the strongest, most durable concrete is also very hard to place properly. Most of us like to pour concrete with a little more slump than you did but never soupy. It's much harder to work with low slump concrete but that's the right way to do it ..... soupier mixes are a shortcut to avoid work.

                            Obviously I can't see what's going on below grade but you piers will likely hold up a deck just fine. There really isn't that much of a load with a simple deck .... all the pier has to do is transfer the weight of the deck to the ground.

                            Comment


                            • #15

                              Re: Concrete Deck Piers

                              Originally posted by dave_k View Post
                              Your our concrete isn't consolidated. You simply didn't manage to get the voids out of the concrete.

                              You can consolidate concrete with a concrete vibrator or you can do it manually..... the way I do this is by rodding it (repeatedly plunging a wood or metal rod into the concrete to get rid of voids) then tapping the sides of the form with a hammer to get a good surface finish.

                              Concrete should be mixed as dry as possible while thoroughly hydrating the cement powder. The problem is that dry mix that makes the strongest, most durable concrete is also very hard to place properly. Most of us like to pour concrete with a little more slump than you did but never soupy. It's much harder to work with low slump concrete but that's the right way to do it ..... soupier mixes are a shortcut to avoid work.

                              Obviously I can't see what's going on below grade but you piers will likely hold up a deck just fine. There really isn't that much of a load with a simple deck .... all the pier has to do is transfer the weight of the deck to the ground.
                              Thanks a bunch, this is helpful info, and good advice for next time.

                              Comment

                              Working...
                              X