# Thread: Building 27' AG Pool

1. ## Building 27' AG Pool

I am constructing my first permanent ABG and have taken the advice given on this forum to heart. I have searched this forum and much of the information either says or implies that there is a crusing weight of water on the pool bottom. Some posts say that the weight of the water will crush a styrofoam bottom or other the pool bottom. It has caused a lot of doubt on my part that I can safely build this pool and why in the world they are allowed to manufacture and sell these pools in such an indiscriminate manner. I decided to apply some basic math to the problem and determined the following:

27' round pool manual says it holds 17,000 Gallons.
17,000 gallons
x 8.5 #/gallon
= 144,500 pounds of water in pool.

13.5' x 13.5' = 182.25 sq feet
182.25 sq ft x pi = 572 sq ft of area for 27' round pool

convert area to sq inches so psi can be determined
12" x 12" = 144 sq in per sq foot.
572 sq ft x 144 sq in = 82368 sq in of area in a 27' round pool

calculate psi on the botom of the pool
144,500 pounds of water / 82368 sq in = 1.75 psi pressing on the bottom of the pool.

I feel after this calculation that I can build this pool without having to over build the pool. I am making this post to help allay fears of other people about the effect of the water pressure on the pool bottom. The foam products that are avail in my area have a rating of 10 - 15 psi crush strength so are suitable for my pool. I talked with another local ABG owner that has had his pool for 5 yrs with a white foam bottom that he say had no divots or other depressions in the floor. These calculations seem to confirm this and the white Styrofoam is less expensive.
I have installed the pads for the uprights and am now leveling the pool floor.

2. ## Re: 1.75 psi pressing on the bottom of the pool

Thought I would add a couple of pictures these show the stepping stones that are ready for the uprights.

3. ## Re: 1.75 psi pressing on the bottom of the pool

Couple more Pictures

4. ## Re: 1.75 psi pressing on the bottom of the pool

You went through a lot of calculations to determine pressure but in reality, you only need to know the depth of the water to calculate the pressure.

PSI = Depth (ft) / 2.31 = 4 / 2.31 = 1.73 PSI

5. ## Re: 1.75 psi pressing on the bottom of the pool

Thanks Mark that sure beats my convoluted calculations. What is the 2.31?

6. ## Re: 1.75 psi pressing on the bottom of the pool

That's the magic number

7. ## Re: 1.75 psi pressing on the bottom of the pool

Yes it is a magic number. It converts feet of head to PSI. For static head, the depth of the water equals the static head so to derive this constant you start with the weight of water which is 62.3832 lbs/cu-ft and then just change the units:

Head ft/PSI = (144 sq-in/sq-ft) / (62.3832 lbs/cu-ft) = 2.31 ft / (lbs/sq-in) = 2.31 ft/PSI

8. ## Re: 1.75 psi pressing on the bottom of the pool

Thanks Mark. The ft/2.31 makes it much easier to find the PSI.
The pool has the bolts holding the walls together spaced very close together at the bottom and to some extent at the top. The center of the wall has a greater spacing between bolts. Each side of the SS panel has 31 bolts and nuts with 13 nuts and bolts in the bottom part of the wall. Is the force of the water pushing out that great?
I have the walls up and will be installing the foam floor and cove today. I was too tired to take pics yesterday but will post some pics this morning.

9. ## Re: 1.75 psi pressing on the bottom of the pool

The force of the water is greatest at the bottom and zero above the water line so that is probably why they have more bolts closer to the bottom. While 1.73 PSI does not seem like a lot of pressure, the total weight of the water is 143,000 lbs so the structure still needs to be fairly strong to hold it back.

11. ## Re: 1.75 psi pressing on the bottom of the pool

A few more pictures as the build progresses. I used 19 pieces of 4'x8'x3/4" extruded foam and 5 rolls of duct tape for the foam floor.
Foam floor complete

Liner removed from box

Laying out liner

All hands on deck to stretch out the liner

12. ## Re: 1.75 psi pressing on the bottom of the pool

Duct tape is not a good waterproof tape. It would have been better (and less noticeable because it is much thinner) to use homewrap/weatherbarrier tape (like for Tyvek).

13. ## Re: 1.75 psi pressing on the bottom of the pool

Nice job on the foam floor !!

14. ## Re: 1.75 psi pressing on the bottom of the pool

Cove being installed and taped -- the cove with the gap had not been installed it was just laid out. All the cove was butted tightly together and each joint taped. The bottom joint between the foam cove and the foam bottom was also taped. The cove tape was a single layer. No tape was applied between the top of the cove and the wall.

J-hook hung over the wall

We adjusted the liner by pulling from different directions to remove most of the wrinkles so the sides hung straight and got all the wrinkles out of the floor. The bottom liner seam fell on the cove all the way around.

15. ## Re: 1.75 psi pressing on the bottom of the pool

Your cove wasn't the peel n stick kind ?

16. ## Re: 1.75 psi pressing on the bottom of the pool

Now comes the Tom Sawyer part. Put about 2" of water in the bottom and told the kids they can play in it. They did not know they were removing the wrinkles. They slid on the bottom in all directions for hours. The foam bottom was smooth and had enough give to allow all the wrinkles to disappear.

There is about a foot of water in it now and the walls are hanging straight.
More pictures tomorrow.

17. ## Re: 1.75 psi pressing on the bottom of the pool

Looks great !

18. ## Re: 1.75 psi pressing on the bottom of the pool

You are going to love that liner! I have the same one!

19. ## Re: 1.75 psi pressing on the bottom of the pool

Thanks Jeff

- - - Updated - - -

Thank you Casey - my DW was hoping that it would not be so blue. Yours look wonderful. I hope we can keep our pool water looking like yours.

20. ## Re: 1.75 psi pressing on the bottom of the pool

Follow Pool School to the T and your water will look just like mine!

I can't remember when this one was taken but it doesn't look dark at all in this pic...

My current avatar and steps into the pool.

How it looked upon opening yesterday.

It looks like your pool will get some shade. My pool is in full sun ALL day long.

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