Pool subsoil

Butcher

LifeTime Supporter
Aug 13, 2010
112
Hello,

I am an excavator by trade and I am going to be building my first vinyl liner inground pool. The house I live in backs onto a ravine with about three to four feet deep of topsoil in the back yard. I need to raise the height of the pool a couple feet to match the grade at the house. In doing this I may only be digging a couple feet deep into the ground to get to the proposed elevation for the floor of the pool where the pool will sit. This could leave still a couple feet of topsoil under the elevation of the pool. I know when I do excavations for basement foundations we cannot put walls on top of topsoil. I guess what I am asking is should I remove the remaining topsoil from under the pool and fill it back up with some sort of aggregate or sand to the height of the bottom of the pool and compact it before doing the concrete floor for the pool?

Thanks in advance,
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Yea, you will need to strip the loom (thats topsoil for non new englanders) out down to what ever is below. You can bring in some processed gravel mixed with chopped up road asphalt (if you have that kind of material) or you can use 3/4" stone. The stone is nice, but it's expensive and overkill, imo. Processed gravel compacted in 6-8 inch lifts will work fine.

Thats a ton of loom by the way :shock: Any way you could sell that? :mrgreen:
 

Butcher

LifeTime Supporter
Aug 13, 2010
112
Thanks bk,

Yes we have that material, we call it recycled concrete. I was going to do the overkill method with 3/4 clear limestone but I like the cost of the recycled much better. I will compact it up to proposed under side of pool.
Getting rid of topsoil up here is no easy task. Gonna probably cost me rather than make anything on it. :hammer:
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Butcher said:
Thanks bk,

Yes we have that material, we call it recycled concrete. I was going to do the overkill method with 3/4 clear limestone but I like the cost of the recycled much better. I will compact it up to proposed under side of pool.
Getting rid of topsoil up here is no easy task. Gonna probably cost me rather than make anything on it. :hammer:
Where are you? Here in Mass good screened loom is worth a bit.
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Ohm_Boy said:
Thought it was loam? Isn't a loom one of those weaving things?
HA!

Well, yea, but in New England, it's pronounced "loom". Just like the town of Peabody is Pee-bu-dee, Quincy is Quinzy, and Worcester is Wu-stah, and the town of Leicester is Lester. :hammer:
go figure. :mrgreen:
 

Butcher

LifeTime Supporter
Aug 13, 2010
112
bk406 said:
Butcher said:
Thanks bk,

Yes we have that material, we call it recycled concrete. I was going to do the overkill method with 3/4 clear limestone but I like the cost of the recycled much better. I will compact it up to proposed under side of pool.
Getting rid of topsoil up here is no easy task. Gonna probably cost me rather than make anything on it. :hammer:
Where are you? Here in Mass good screened loom is worth a bit.

I'm located in Toronto Canada. Too much topsoil in my area.
What is the best material to use for the bottom of the pool in a cold winter climate? How thick should it be?

Thanks
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Define bottom. Do you mean the soil underneath the bottom, or the substrate right under the liner? If it's the latter, a sand/portland mix with a bit of fly ash is good. Almost the consistency of tile grout. No aggregate is needed. make it ~4 inches thick. Lots of guys use straight vermiculite, but IMO thats a cheap way to go and it wont hold up near like portland/sand mix. They do it because its cheaper and they can drop the liner in faster.

In terms of substrate under the concrete floor, depnds on whats there. If its virgin soil with a little clay in it, compact the devil out of it with a plate compactor and your good to go. What does your subsoil look like?
 

Butcher

LifeTime Supporter
Aug 13, 2010
112
Yes, I was talking about substrate under the liner. I saw a video that showed to put about 2" of poolcrete but 2" didn't seem thick enough to me. I thought I read somewhere that a two stage aggregate concrete base with a sand concrete finish coat could be used.
I read a couple articles that said the vermiculite was better than sand because it was less abrasive than sand, more porous to allow for a raise in the water table and better insulation from the cold earth. Of course these where from the manufacturers of the vermiculite.

I believe in my climate pool companies are using a sand concrete mix but not sure if they are just using it in one stage or a two stage. Wasn't sure how thick either.

The substrate under the concrete floor will have to be compacted recycled concrete to replace the extra depth of the topsoil. Under that below the topsoil layer I believe will be a silty clay.

I do back onto a ravine with a water shed that runs water when it rains and stands water during rainy months. The water table is pretty high here. I'm sure if I dig down 4' water will start to fill the hole.

Should I raise the pool up as high as possible to try and stay above the water table or will that not be necessary?
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Pool crete is good stuff. Vermiculite is better than sand, but 4" of pool crete (which is bascially portland/sand) is the best, IMO. It looks like tile grout coming out of the truck. Its a fairly dry mix You dont want aggregate in it either, really. Get your bottom compacted, shoot the grade again and if you need to stake the grade out on the slope or in the hopper run the pool crete up to the top of the stake and pull it just like you would a foundation.

If you have ground water, put a well point in so you can pump it out if you need to. It's done all the time.
 

Butcher

LifeTime Supporter
Aug 13, 2010
112
bk406 said:
If you have ground water, put a well point in so you can pump it out if you need to. It's done all the time.
During construction only or past that as well? Once the pool is in and full of water is it still affected by the water table?
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Yea, you need a dry well. If the ground water gets high enough, it can float the liner if you have to drain a little water for whatever reason. The most likely thing is you will get water behind the liner and it will bulge during heavy rains. A dry well with pump will take care of it. Just put it in when your building the pool.
 

Rico Laguno

Active member
Aug 19, 2010
35
Nyack, NY
Curious, you mentioned that pool crete (sand/portland) is the best of the 3 bottom options for a liner installed pool. However, I have noticed most builders in the NE quote out their pools with a vermiculite bottom. Can you guys expand a little on what actually makes the pool crete a better option?....is it sturdier?...better feel?

I think if you could expand a bit on this, it would help some of us who are also following this thread make better decisions
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
Well, like anything else, I guess it's a matter of opinion. Vermiculite is used a lot. It's pretty easy to do and goes down fairly quick. I think in general it does wear faster since it's softer. It's only a few hundred PSI, if that. So..if you have weight on it, over time it will get bumps in it. It actually wont hurt anything, really. Unless it gets too bad, its not that noticable in the day time.
"Pool crete" is basically a mix of porland, sand, and some times either a bit of vermiculite or fly ash. It's more expensive to do that way, but it wont get lumpy and bumpy like straight vermiculite will. It's ~3000 psi so its really durable. On a liner change, the potential to have to re-do or repair a vermiculite floor is higher than pool crete, for sure.
I wouldnt get too worked up over the use of vermiculite over pool crete, really. Both are good options. That being said, ifa builder offered pool crete over vermiculite, I'd opt for the pool crete. But, if i liked a particular builder for price, service, etc and he only used vermiculite, I wouldnt turn him down over it.
 

Butcher

LifeTime Supporter
Aug 13, 2010
112
I realize that, which is why I posted earlier that the info I got was from a manufacturer. :wink: :cheers:

Just thought someone else might like to read the article.

With the high water table where I live it might be a good option though. I am going to bring my machine in soon and dig a test hole to check soil conditions. Hope to start excavation of the pool sometime this week. I will post lots of pics as I go along. Headin' out back now to start marking the ground.
 

Other Threads of Interest