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Attended NCMA Class Today and....

Discussion in 'Hardscaping' started by LB1234, Feb 19, 2008.

  1. LB1234

    LB1234 LawnSite Gold Member
    Messages: 3,208

    I dunno I'm still really confused about the yes/no/maybe on weather or not filter fabric should be used behind the drainage stone.

    According to NCMA its not necessary and could cause more damage than good...yet engineered plans will call for it...yet the speaker today said we could use it provided it has an "adequate" permeability.

    :dizzy::dizzy::dizzy::dizzy:SO WHICH IS IT:dizzy::dizzy::dizzy::dizzy:
  2. amscapes03

    amscapes03 LawnSite Senior Member
    Messages: 398

    i took the class last month along with an employee of mine. i always have used filter fabric, and always will. it just makes sense to keep your drainage stone clean. Hey LB, was your class based on construction of 35' - 70' walls?
  3. LB1234

    LB1234 LawnSite Gold Member
    Messages: 3,208

    I wouldn't say a specific height but it definately was geared toward LARGE construction projects. To date we have yet to do a wall over 32 or so inches.

    Like I said the class was okay. But when we asked questions it was like well thats not on the test but we can go over it if you like...I dunno. Its like we were rushing to get out early so we can pay them get on our way and receive a piece of paper.

    Again, can anyone answer or elaborate on why engineers will spec for filter fabric but NCMA states it is actually detrimental to the 'global stability' of the wall? Anyone? Please?
  4. Paver Gangster

    Paver Gangster LawnSite Member
    Messages: 144

    I wonder where the instructor got that information.

    According to what I have read the NCMA has two positions on this issue:

    1. The filter fabric water flow rate should exceed the water flow rate through the system. Thats where an engineer needs to come in.

    2. This method is OK for many or most wall applications (I forget the exact language).

    Of course, the two books I have are from 1997 and I think 2002.

    Unless there is a new Tek sheet from NCMA that addresses this. Bears research. I know Anchor RWS preaches against this, dont know about other licensors.
  5. Paver Gangster

    Paver Gangster LawnSite Member
    Messages: 144

    "In some cases a geotextile filter is installed between the drainage fill and the infill to protect the drainage fill from clogging."
    NCMA Tek 15-8 which I beleive is from 2004 or 2005:

    Page 7, detail B
    NCMA Concrete masonry Designs, April 2004

    "Drainage fill: Drainage fill is free-draining granular material placed behind the wall to facilitate the removal of groundwater and minimize buildup of hydrostatic pressure on the wall. It is sometimes also used to fill the cores of the units to increase the weight and shear capacity. The dry stacked method of construction used for segmental retaining walls permits water to drain through the face of the wall, aiding in the removal of groundwater. In some cases, a geotextile filter is installed between the drainage fill and the infill to protect the drainage fill from clogging."
    NCMA website

    I'm beginning to think that EP Henry instructor might work for Anchor Retaining Wall Systems?
  6. iowa

    iowa LawnSite Senior Member
    from NW IA
    Messages: 305

    You make this post sound like you put the fabric between the drain stone and native soil. Just wondering if thats what you actually do? I think they call for the fabric to be behind the wall. Either way, I don't use it.
  7. Majesticman

    Majesticman LawnSite Member
    Messages: 76

    We only use it if it is spec'd by the eng. I think the reason it was ever started was to stop the bleeding of soil though the wall.

    Our area has a rock that will compact and not leave a path like washed gravel will but I noticed in areas where a lot of washed rock is used Gray walls are usually soil stained.
  8. LB1234

    LB1234 LawnSite Gold Member
    Messages: 3,208

    But this is my point.

    Say I receive my certification through NCMA and my next job engineer says use filter fabric AND in my contract I state we will build wall NCMA spec's.

    Technically, my contract could be voided, no?
  9. jbailey52

    jbailey52 LawnSite Bronze Member
    Messages: 1,094

    I think your contract should state they way you will build it, but once there is an engineer signing off.... you need to amend your contract to reflect the changes the engineer makes. Your following his instructions per liability issues.
  10. Paver Gangster

    Paver Gangster LawnSite Member
    Messages: 144

    The NCMA, like the ICPI, only certifies that you took the class, and passed the test, not that you install to NCMA recommendations (not specs).

    Your contract should state that you install to NCMA guidelines, except when otherwise specified by a licensed wall engineer for a specific job, or if the client elects to not pay for an engineer, to manufacturer's specifications which may or may not coincide with all NCMA guidelines.

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