Vermiculite concrete floor cracking


Aug 9, 2022
Pool Size
Salt Water Generator
Hi Everyone,
I am new to this forum and am hoping we can get some help.
We are in the process of having a liner pool constructed.
A few days ago they came and put in the floor which is comprised of Vermiculite, Concrete , and Polymer ( pool mix). After two days we are noticing extensive hairline cracks throughout. The pool company is telling us it’s not an issue and happens because of hot weather or wind.
We aren’t so happy about it and don’t think that new pool should look like that.
Please see attached images and let me know your thoughts; Should we insist that they fix it before putting in the liner or just let it go? TIA


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TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
The vermiculite layer is not a "structural" component of the pool. It's purpose is to create a smooth and continuous bottom for the liner to rest on. It's also a porous material that is going to allow ground water to permeate through it. It terms of it's thickness relative to all the other structural components, it is basically like an eggshell and it will crack especially when the forces from hundreds of thousands of pounds of water come to rest on it. But those same forces will hold everything in place and allow the vinyl liner to be protected from the ground it is resting in. Ten to fifteen years from now when that vinyl liner gets changed, if you still happen to be around, you will be horrified at the appearance of the vermiculite layer or, at least, the pieces of it that will still be there.

This is one of those "sausage makers" moments - if you ever want to be able to eat sausage, don't watch how they are made ... likewise, it's best not to look too critically at the intermediate steps of a pool build unless you want to be upset every day of the build.
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