How do you guys keep your walls perfectly straight?

Discussion in 'Hardscaping' started by cards1, Jan 6, 2009.

  1. CertPro

    CertPro LawnSite Member
    Posts: 139

    Zedosix - What is your thought process for switching between the two setting medium? I thought stone dust was a major no no
  2. zedosix

    zedosix LawnSite Silver Member
    Posts: 2,635

    I should call that stone screenings, not stone dust. I like to use stone screenings because it will pack harder and stay in place whereas sand will wash out with time.
    We use sand as a bedding layer for pavers because we want our brick to sink in when compacted, we want that sand to pull up into the brick joints and lock together as one unit. We then use restraint edging to hold the laying field in place. Now with a retaining wall we have one straight row of block, if we set that on an inch of sand there really is nothing to prevent the blocks from moving forward or sinking unevenly into the sand. A retaining wall usually has some amount of water directed to the base as well, and the sand will likely wash out over time faster than stone screenings.
    When our co. installs walls, we always bury one row (laid on screenings) and on the second row up we put a restraint edge.
  3. Hard at Werk

    Hard at Werk LawnSite Member
    from MA
    Posts: 19

    When we put up a wall we put in a base of at least 8" of crushed 3/4 stone depending on soil, water buildup etc.. level the stone using a laser as if i were to lay on it and then pack it like crazy. Then put about a half to three quarter inch of 1/4 stone (small clean stone no dust), and lay on that fine stone adding or subtracting 1/4 stone. Backfill with 3/4 clean stone ( NO GRAVEL !!!) at least a foot (depending on soil, height, water etc...). :weightlifter:
  4. CertPro

    CertPro LawnSite Member
    Posts: 139

    But doesn't the excessive amount of fines in screenings promote uneven settlement over time? Not to mention the breakdown of the screenings themselves.
    Last edited: Jan 7, 2009
  5. zedosix

    zedosix LawnSite Silver Member
    Posts: 2,635

    Guess that depends on how much you are using. We screed our granular to within 1/2" or less then add just enough screenings to level our base. How is this going to become uneven if our base is compacted and leveled first. Don't forget in a vehicular application (pavers) we have cars, trucks pedestrian travel, salt etc, this is where we can see a breakdown of stone dust. Not on a retaining wall, you lay the block it stays put. With sand all I am saying is it just moves to much with the initial laying of the base block, I'm sure if there was only 1/2" of sand and all methods of srw construction were practised, it would likely stand the test of time as well as stone dust.
  6. ford550

    ford550 LawnSite Member
    from PA
    Posts: 221

    NCMA allows screenings or sand to be used in retaining wall installations, they have indicated that either one is acceptable. Paver installations, screenings is not acceptable only concrete sand.
  7. STL Ponds and Waterfalls

    STL Ponds and Waterfalls LawnSite Bronze Member
    Posts: 1,177

    NCMA does spec up to 1" of course sand for SRW setting base, but I prefer 1/8" stone with dust. I tried the sand on one small seating wall and the jury will be out on that one for awhile. Screenings once setup after install is like concrete (but flexible)! I'm still worried about sand washing out, but if your base is setup right that shouldn't be an issue. Unless your setting in a thick bed of sand. If you screed your base in the first place you shouldn't need a setting bed, but that's in a perfect world.
  8. Hard at Werk

    Hard at Werk LawnSite Member
    from MA
    Posts: 19

    That's why we use fine crushed stone almost like a peastone but more angular. What it is that this stone is considered to be trap rock, just fine trap rock. Very easy to work with and there is no dust variable that will hold moisture or settle as much as screenings. It's clean and sizes range from about 1/8 to 1/4 . Even if NCMA does allow for use of concrete sand, I don't like it because its round and tends to move more and wash faster than trap rock.
  9. AztlanLC

    AztlanLC LawnSite Bronze Member
    Posts: 1,045

    I have being using 1/4" inch for quite sometime now and it works really good I use it for patios and walkways as well.
    Before we use to use sand or stone dust mixed with portland to avoid any sand migration but now it's only 1/4" or even 3/8"

    As far as keeping walls straight just use a string and the next rows have to be somewhat straight.
    If you try to use the string on every course then you end up not aligning the blocks with the pins lock up 100% and even you have a straight wall overtime the force coming from behind will push that wall out, in the best case scenario it will align the block to the ping worse it will force the block out and failure will start at that point.
    from time time to time some rows will vary they will not stay as the base row but unless the difference is a lot we fix misalignment once we install the coping.

    PS by he record I don't care what anyone will say about using it for patios and walkways this topic has being discussed several times so let's not start another bedding material tread.
    Last edited: Jan 8, 2009
  10. zedosix

    zedosix LawnSite Silver Member
    Posts: 2,635

    Its ok, not everyone is doing it the right way:)

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