What is under my vinyl liner?

Player1

Member
Aug 25, 2018
8
Missouri
I purchased a house with a pool a couple years ago. When I purchased it, I noticed grooves in the bottom of the pool. They look like erosion trenches. I have attached a picture to show you what I mean. I think one or two more have appeared over the last couple of years.

The bottom of my pool feels solid iPoolMathn most places. However, some places feel squishy under the liner, like mud or sand. These spots seem to be near the top of the erosion trenches. So, what is under the liner? Why isn't it all solid?

My liner is between 10 and 12 years old and I think it's pretty close to replacement. I'm trying to figure out what kind of repairs are needed when the time comes. Will I need to do something to repair the trenches? Can you help me figure out what type of material my pool is made out of under the liner? The walls feel rough and even jagged under the liner almost like course concrete that wasn't smoothed over properly.

Edit: I think I may have posted this in the wrong section. Sorry about that. If a mod sees this, feel free to move it where it is supposed to go.
 

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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,802
Tucson, AZ
Depending on construction practices in your area, a vinyl lined pool can either have a sand base (cheap and low quality) or a vermiculite base (higher quality but more expensive). Vermiculite is a type of very smooth but porous cement and it is usually hand troweled along the bottom of the pool and up to the sidewalls. Vermiculite is used to allow water to permeate it so that high ground water doesn’t do anymore damage than cause a liner to float. A vermiculite base can break down over time and erode away but a sand base can easily get washed away.

Sounds like you’ll be doing a liner change in the near future. If so, budget money for repairs also because it sounds like your pool base will need work too. If the base is not vermiculite, then pay to have it properly applied when you change the liner as vermiculite is the gold standard for pool liner bases.
 
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Player1

Member
Aug 25, 2018
8
Missouri
Thank you. That helps a lot. I guess I will wait to see what I have when I pull up the liner. I have learned in another thread that it probably isn't in my best interests to replace the liner myself, but do you think I could do the pool base repairs fairly easily?