Using styrofoam under a walkway

Discussion in 'Hardscaping' started by Woodland, Jul 25, 2007.

  1. Woodland

    Woodland LawnSite Member
    from Maine
    Messages: 207

    The project is to rebuild a small brick walkway, about 15' long. The current walk has heaved quite badly due to freeze/thaw in the spring. The previous installation was not dug down very deep and only sand was used (according to the homeowner). In addition, they get a lot of water flow in the spring. The soil is clay and the house is situated on a moderate hillside. I need to rebuild and alleviate the drainage/freezing issues. Rebuilding with a good sub-base will likely eliminate most, if not all of the problems but I don't want to take any chances. Also, the homeowner has talked to "others" who have suggested putting Styrofoam insulation under the walkway, similar to what is often done under cement slabs. I've never done this before, however, but it doesn't seem like a terrible idea. At the very least, if the walk does move, it will move in 4' x 8' sections! Anyway, my plan is to excavate deep and fill/construct with the following:

    1. Geofabric over existing subsoil
    2. 5" of 3/4 compacted crushed stone with drainage pipe that will exit from the side of the walkway
    This should allow any water traveling through the ground to move freely under the walk and out the drain pipe
    3. Geofabric over the stone to prevent mixing
    4. 4" compacted gravel
    5. 1" sand bedding layer
    6. Brick

    So where should I put the styrofoam? Seems the most logical place would be between the gravel and the sand BUT would this prevent water from percolating through the walkway, thus keeping the sand layer saturated and prone to freezing and heaving, and second, will the foam, that close to the surface make the walkway spongy?
  2. waltero

    waltero LawnSite Member
    Messages: 206

    It won't work!!!

    Have you ever filled up the ice cube tray? Did you notice that the cubes get bigger when frozen. That is what is happening in the ground when it freezes. When the ground freezes it has no where to go but up. Unless you plan on heating the ground so that it never freezes you can't stop it.

    The whole benefit to pavers is that they remain flexible during the winter and in the spring the ground will settle back down and the pavers will also with no damage as you would get with concrete.

    Just follow ICPI guidelines, drainage is very important and you shouldn't have any problems.
  3. ChampionLS

    ChampionLS LawnSite Bronze Member
    Messages: 1,066

    Wholly Molly. Way too complicated.

    Here's something to think about:
    I would completely lose the idea about the Dow foam board. All you need is some insects or rodents to chew it apart, and the whole thing will fail.

    The walkway heaved because there was NO base. As a simple homeowner project, somebody just put sand down and bricks on top. (sounds like my dad!) It will work and last for a few years, and eventually become wavy or worse. If you install the walkway as all the manufacturer's recommend, it should be trouble free forever.

    Excavate 9". Wrap your excavation with Geotextile separation fabric-and up the sides. Install 6" (nominal) of 3/4 modified stone, and compact in 2" lifts. Install 1" of concrete sand (no fabric layer) on top of your compacted base. Use PVC or Electrical EMT tubing etc. to evenly screed the sand. Lay your bricks on top of that. There are many edge restraint options. Usually a plastic edge restraint and 12" spikes are used. All exposed edges need to be restrained. After that, your ready to tamp. For clay bricks, place a sheet of Luan or Plywood on top and compact. Sweep dry sand on top to finish. If you want to avoid the natural moss that can grow in the joints, sweep in Polymeric joint sand, and lightly wet the area with water. Trim the excess fabric, finish off the sides with topsoil and enjoy.
  4. Woodland

    Woodland LawnSite Member
    from Maine
    Messages: 207

    Why would I wrap the geotextile up the sides of excavation? What mfg recommends that?

    Also, from the original post, there is a large amount of water runoff down this hillside, thus the layer of compacted crushed stone with drainage. Aside from the styrofoam, the walkway construction may be a bit over-designed but not wrong.

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