sand and retaining walls

Discussion in 'Hardscaping' started by AllHardscaping, Jun 8, 2009.

  1. AllHardscaping

    AllHardscaping LawnSite Member
    Posts: 77

    Has anybody used a thin layer of sand over the top of your compacted gravel base to create a level setting base for retaining wall block? I always used a little bit of the fines from the grade 8 gravel but I saw a guy screed a really thin layer of sand on top of the gravel.

    If you have done this how has it worked out. Any problems in the future? Do you just tamp with hammer to set them? How deep do you normally have the sand?
     
  2. STL Ponds and Waterfalls

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

    When I got my NCMA cert they speced 1" of sand for a setting base as well as screenings (3/8 with fines. I did a small seat wall and some pillars last year set in a 1" sand base and haven't seen any problems. I still prefer using screenings and 3/4 minus instead of sand. I only used the sand on that job since it was there for the paver patio.
     
  3. AllHardscaping

    AllHardscaping LawnSite Member
    Posts: 77

    I got NCMA certified a few years back and they didnt have anything about sand. Maybe things have changed. It would be a lot easier going that route. I am just not convinced that it would be the most stable, especially a full inch. Thanks for sharing your experience with it.
     
  4. Bru75

    Bru75 LawnSite Senior Member
    Posts: 585

    I started doing this last year, and the results have been great. I use 3/4" pipe to screed the sand (concrete sand).
    The base still needs to be as level as you can get it, but this way you don't have to worry about those few gravels that are a little high and cause the block to rock back and forth.
    Saves a lot of time.
     
  5. AllHardscaping

    AllHardscaping LawnSite Member
    Posts: 77

    Interesting. When you say concrete sand do you mean just a well graded sand like you use under pavers or something that actually has concrete or portland in it?
     
  6. Bru75

    Bru75 LawnSite Senior Member
    Posts: 585

    The same as you use under pavers.
     
  7. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Posts: 6,412

    We frequently will use 1/2 inch of sand. Basically we get the gravel as close to perfect as possible (in terms of grade). Then we place approx 1/2 inch of sand and set block. The other week we had 100-feet of Cornerstone block (weighs approx 66# each) set in under 2 hrs. When I returned to the site I saw all this sand all over the footer. I thought "good god, they must have an inch of sane under that block". So I checked the thickness of the sand and I'd guess it was around 1/4".

    So, now I said we do 1/2-inch. Ok, well by the time you tamp the block into place, level, check elevation with laser - there's probably 1/4" under the block.

    We haven't had any problems yet. Like I said, you have to use it sparingly, and exercise common sense.
     
  8. AztlanLC

    AztlanLC LawnSite Bronze Member
    Posts: 1,043

    I like using 1" of 3/8 or 1/4" stone as the setting base but if we have to use sand we mix it 4:1 with portland
     
  9. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Posts: 6,412


    Why??




    ,
     
  10. AztlanLC

    AztlanLC LawnSite Bronze Member
    Posts: 1,043

    I don't want to risk the sand to migrate or wash out and I know 3/8 stone won't.
    I should've mentioned that when we use sand is only 1/2" or less thick and it gets mixed with portland
     

Share This Page