Nervous about my pool bottom material!


Jun 27, 2010
I'm having a pool installed now... water is going in as I type! 21 x 40 inground vinyl liner pool. Last week we had a bad heat wave (massachusetts). The pool company usually uses vermiculite for the hard bottom. But they didn't like how the vermiculite was mixing last week so they went to concrete/cement. They kept saying it's more expensive and stronger this way... they didn't want to do it but had no choice and ate the cost. Then the deep end sides went on last Friday... using a different concrete. Over the weekend, we poked around and went in it and it was hard, crumbly, and not smooth, bumps everywhere. Today they sanded it around the sides and went over the cracks with a vermiculite and within 2 hours, had the liner on and in goes the water.

I heard vermiculite bottoms are softer and better! Cement tends to crack and create sharp edges and can do a number on the liner. We expressed concern but they say they are experts and not to worry about it... we have an overbuilt solid pool.

Anyone have experience with any of this???


TFP Expert
LifeTime Supporter
May 10, 2010
SW Louisiana
In 30 years of dealing with a cement/concrete bottomed vinyl lined pool the only problems I have seen is when crawfish will tunnel under/through the concrete and cause a small 1-2 inch sink hole in the liner. Sometimes these sink holes develop small pinhole leaks after months or even years, which can usually be patched fairly easily (SCUBA gear helps if the leak is in the deep end). These minor sink hole imperfections are easy enough to patch when the vinyl liner is replaced. Things may be different in your part of the country where the ground likely freezes in the winter.



Well-known member
Dec 3, 2009
Central Massachusetts
You wont have any problems. I have concrete (pool crete actually). Mix of portland, sand and a bit of vermiculite. There is no aggregate in it. It's almost like grout. Yes, it's more expensive. Vermiculite is used because its cheaper. A pure vermiculite pool bottom, IMO, is inferior to pool crete.

If they finish it correctly, it wont crack and there will be no bumps or rough edges.

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