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Thread: Aggregate for base - help with my layers please!

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    Aggregate for base - help with my layers please!

    We have on order a 27 foot round steel above ground pool. We've dug out our area using a tractor to make it more or less level, and I'm working now on hand levelling the rest. Ground is undisturbed, with some clay (I can squish the dirt in my hand like playdoh). We live in Canada, with a lot of frost heave and full, full freezes in the winter. Our pool instructions call for trenching and laying 2inches thick of "rock dust" or mortar in a circle around the pool, 24inches wide, and the footings and rails will sit on top of this. Pavers are optional in the instructions, due to frost heave, and I feel we'll be best off just putting the uprights/footings right on this compacted rock-whatever trench (open to corrections )

    After calling around to the landscaping companies around here, all are suggesting a 25mm washed rock to use, as it will compact nice and firm, and allow for water to drain through the rocks to help us with drainage and frost heave.

    So, here's what we are thinking....and where I need help with my layers:

    1) Lay down a 2inch thick base of the washed rock over the full area (not just in a trench). So now we have a giant circle of rock. Of course will compact it down, level it, compact again, etc etc so it is firm.
    2) Install the pool walls and uprights on this base.
    3) Inside the pool, my understanding now is that I need to install my foam cove AND THEN put in material for my liner base, like foam or sand or foam and sand (Logic tells me I should do the base and THEN the cove.....but I'm reading otherwise?)
    4) This base inside the pool.....we are going to get 1inch of the extruded polystyrene (can't afford the 2inches ), and then we need something for between the washed rock and the foam.....we can a) use the appropriate sand or b) use more of the washed rock. If we go with sand, and underneath the sand as our main base is this washed rock, will the sand not just wash out into the cracks of the gravel? If so, should my layers be: washed rock, a liner or tarp, 1inch of sand, 1 inch of foam, then the pool liner?

    Does this all sound like the appropriate pool sandwich, so to speak? Or would you just trench out the 24by2inches for the washed rock, and then put your inside base right on top of the soil?

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    Casey's Avatar
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    Re: Aggregate for base - help with my layers please!

    If you're going to do the whole pool base in crusher ( what we call it here), then I'd do the crusher, set pool up, foam under layment, cove and then liner.
    I'd bet you my bikini you'll never get TFP water from a pool store!

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    Re: Aggregate for base - help with my layers please!

    Ok, perfect. Do you think the 1inch foam over the crushed rock will feel ok on the feet? And, so there is no real reason I need a 2inch base in there under the liner (like, the liner doesn't need that specific depth for any reason?)

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    Casey's Avatar
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    Re: Aggregate for base - help with my layers please!

    You should be fine. Triple tape your seams with heavy duty tape.
    I'd bet you my bikini you'll never get TFP water from a pool store!

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    Re: Aggregate for base - help with my layers please!

    I used 3/4" form under my pool and it is great. As stated, tape the seams. I used the extra wide gorilla tape.

    I also used the crush and run stone as the initial base, compacted down and it was by far the best thing that I did. I basically set up like concrete and provides an extremely solid/stable base.
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    Re: Aggregate for base - help with my layers please!

    Synergy2, you put the 3/4 foam right over the crush and it feels nice on the feet? This is all making me feel so much better Thank you both!

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    Re: Aggregate for base - help with my layers please!

    Her contractor is not recommending "crusher", or crusher run, or crush and run. or QP, or Quarry Process, or what is properly called Dense Graded Aggregate, or DGA

    DGA is a well graded mix, meaning it has an even amount of all sieve sizes from 3/4" down to fines (dust). This is what allows it to both pack quite densely and also have a very forgiving Proctor curve (it will compact to an adequate density over a fairly large moisture content range).

    Her contractor is recommending 25mm WASHED rock. Washed means it is POORLY graded - all the fines are washed out. It consists of nothing but 25mm pieces of stone, nothing bigger, and nothing finer. It will have a lot of voids in it. This is recommended to allow water to drain and hopefully mitigate the frost heaves that can happen in poorly draining soils (such as her native soil).

    20mm is roughly 3/4" - I assume your contractor wants to put in 3/4" clean crushed stone (as opposed to 3/4" round pebbles). For those in the US, 3/4" clean is what most people call "gravel" - those big piles of angular grey "rocks" that are about 3/4" in diameter that you see at construction sites.

    2" of 3/4 clean, especially over clay soils that are pumping, is not that much. Once you begin to compact you are going to embed at least an inch of it into the soil. Not much drainage. I honestly would be leery of putting 1" of foam board of 3/4" clean. I think ti would begin to break down, collapse into the void spaces, and then telegraph the underlying stone through to the bottom. I would go with a ring of stone, and sand (or DGA) in the middle.

    Take my advice for what it is worth - I am not a pool contractor, and my 27' ABG is on sand (on sandy fill that has been in place for at least 40 years). I was an engineer for an earthworks company - but that was many years ago and we did dams, foundations, soil testing, and pile driving - nothing involving foam board over stone, covered with vinyl under 4 feet of water.

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    Re: Aggregate for base - help with my layers please!

    Thank you so much for your post! I called two of the major rock-providers here, and neither really seemed to know what I was asking them, but both recommended the 25mm. I asked the second company about their 'road gravel' which has finer particles mixed in, and he thought they would just wash right out. Now I'm really wondering what to do... Phonedave...would you go with the washed rock even for the ring? Or should I keep phoning around until I find someone with the DGA you speak of? I wonder if my location is limiting my options, as so far I've seen nothing with remotely those keywords on these company websites.

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    Re: Aggregate for base - help with my layers please!

    I used the 1" Durofoam that contractors put under concrete poured floors, works great! Home Depot sells here in Manitoba, so chances are they do in in AB.
    http://www.homedepot.ca/product/duro...x-1inch/940438
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    Re: Aggregate for base - help with my layers please!

    Thanks for the suggestion, DarrelB! We're going to head to Home Depot today and see what they have

    And, I think I found the right aggregate..is this the 'crush' you are all referring to? "25mm Crushed Gravel is a mixture of sand, rock fines and rock that is best used as a packing gravel for underneath asphalt, concrete, driveways, garage pads, retaining walls and paving stones. It is a compaction material also known as 3/4" crush and road crush."

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    Re: Aggregate for base - help with my layers please!

    Quote Originally Posted by StephL View Post
    Synergy2, you put the 3/4 foam right over the crush and it feels nice on the feet? This is all making me feel so much better Thank you both!
    YEs I did. After I dug done to level, my pool base was essentially all clay just like yours. I compacted 3 yards of crush and run and then laid down the foam. I have never had any drainage issues or frost issues. This past winter was one of the coldest we have ever had and there were no problems at all. Once the snow melted, my foam was still in place just as I had left it when I took the pool down last fall. We also had 6.5 feet of snow in three days this past NOvember before the ground was even frozen. Nothing washed away.

    I did have to get new foam this year due to a bout of strong winds that broke a few pieces. However, the compacted base was as solid and true as when I laid it.

    - - - Updated - - -

    Quote Originally Posted by StephL View Post
    Thanks for the suggestion, DarrelB! We're going to head to Home Depot today and see what they have

    And, I think I found the right aggregate..is this the 'crush' you are all referring to? "25mm Crushed Gravel is a mixture of sand, rock fines and rock that is best used as a packing gravel for underneath asphalt, concrete, driveways, garage pads, retaining walls and paving stones. It is a compaction material also known as 3/4" crush and road crush."
    Yes, that's it.
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    Re: Aggregate for base - help with my layers please!

    Ditto what Synergy2 said, it is what we used under our pool and had flooding rains this year, no issues, and it did not settle, we are on our second year with this pool.
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