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Deck foundation gravel or concrete?

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  • Deck foundation gravel or concrete?

    I'm building a tent platform/deck out at the lake.

    Back of the deck will be on cinder blocks but the front will have to be 2-3 feet off the ground due to the slope.

    Soil is "poor", sandy silt or silty sand. No permafrost south facing on a side hill drains well goes basically from snow covered to dry very quickly.

    I have some 4x6 treated timbers to use for my front corners and I was going to concrete them in using sonotubes, but now I've read some advantages of just burying them using gravel which is easier, maybe about the same cost or a little spendier oddly enough, and easier to remove (don't think we ever will though)

    the main advantage I've read about the gravel is it supposedly keeps your below grade wood DRIER as the water goes right through the gravel vs possibly being held in by the concrete

    any thoughts on this??

  • #2
    I have done some construction work in the past and in situations you are refering to i don't see any need for concrete, cement, or gravel. If you are using treated lumber and it is deep enough, there is no real need for cement or gravel of any kind. The practice of filling pier holes with cement may be required in some areas of the country by code, but most of those are in flood or high wind areas, and gravel fill is usually only required in areas where drainage is poor. Another thing to consider is some "professionals" will fill around everything because it costs more! Sounds funny, but if you think about it its not really that suprising considering alot of guys will charge a % of the materials for labor, so the more materials they use the more they can charge for labor even though it takes the same labor to fill with earth as it does to fill with gravel. If you do reuse the material that was removed from the hole, try not to fill with any rocks larger than 1/2 of your fist due to the chance they can actually help frost push against the wood. Just a note: if the back of your deck is floating on top of the ground and the front is on piers that are dug in, don't expect it to stay level, the blocks can settle into the ground and drop several inches in sandy soil in just a few years with weight on them, i would put the whole thing on piers. Well thats just my $.02 and I hope I helped, and good luck with your project.

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    • #3
      the timbers I'm using are pressure treated and weathered
      but I'm thinking just buried in dirt they'll still rot out in a few years
      would you re-treat them with something?

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      • #4
        use pier blocks with adjustable brackets. So if it does sink or frost higher you can adjust each corner to level it back out.

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        • #5
          Originally posted by gottago View Post
          the timbers I'm using are pressure treated and weathered
          but I'm thinking just buried in dirt they'll still rot out in a few years
          would you re-treat them with something?
          the chemicals they use for pressure treating wood is forced way into it and contain heavy metals which don't go away easily, don't be fooled by surface looks, most of this stuff that is 20+years old can still be just as stable as new stuff from the store.

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