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What Is A Vermiculite Pool Floor

What Is A Vermiculite Pool Floor

You know what vinyl liner pools look like. You probably know that they’ve been a common inground pool for many years. You know that the surface of a vinyl liner pool is the liner itself. But do you know what lies beneath that liner? Do you know the surface beneath the surface? Do you know the not-as-pretty material used as the pool’s foundation?

Well, we’re here to answer all of those questions for you!

We’ve pretty much seen it all when it comes to pools, and yes, that includes vinyl liner pools! We install vinyl liner pools every year, so we have a great deal of experience with laying their foundation with precision and care.

And that foundation consists of a material called vermiculite, which is what we’ll be getting into in this article. We’ll tell you what it consists of, it’s advantages, disadvantages, and much more.

So, let’s get started!

What is Vermiculite?

Vermiculite is actually a mineral that expands when heated and often exists in the form of clay. However, what we use for inground swimming pools is a little different.

For our use, vermiculite is a mixture of the mineral known as vermiculite and Portland cement.


When preparing to lay the foundation of the pool, vermiculite must be mixed with water. It comes in bags as a dry mix, so upon mixture with water, it turns into a material with a similar consistency as cement. This allows for the vermiculite to be spread and smoothed out along the pool floor to create a stable but forgiving base because of its relative softness.

Process of Application

The process of applying the vermiculite floor of a vinyl liner pool is pretty simple, but pretty complex—we know, it’s weird.

The vermiculite comes in bags and its form is similar to sand. We pour that material into a bucket, wheel barrel, etc. and mix it with water. Sounds simple, right?

Well, the amount of water added to the vermiculite has to be precise to get the correct consistency of the final product. Too little water can create a product that is too dry and unable to be smoothed out correctly; too much water can create a product that is too similar to a liquid and therefore will not be able to create a firm base for the pool. So, you can see why the perfect ratio of vermiculite and water needs to be reached to create the right result.

Once the vermiculite is created, it is then applied to the pool floor. This process can be a lengthy one as each section of the floor needs to be at a specific depth to meet the pool’s specifications. So, it takes time to smooth and level out the vermiculite accordingly.


We’ll typically start at the deep end of the pool as well as the sides where the floor meets the wall panels, working our way towards the shallow end of the pool until completion.


The softness of vermiculite is actually a pretty hefty advantage for vinyl liner pools. It’s softer than grout, the other option for vinyl liner pool floors, and doesn’t harden in the same manner as concrete but not as hard. And when constructed correctly, a vermiculite floor will be fairly forgiving to anything that happens to get under the liner like rocks.

Another advantage of vermiculite is that it reacts well with wet soil and areas that are at a higher risk of producing ground water. Since the vermiculite we use is created with water, exposure to water once it’s laid as the foundation isn’t very detrimental. However, frequent exposure can lead to eventual damage.


A significant problem with vermiculite is that it can be more difficult to apply as the base of the pool. Even though it is a softer material, once it is applied and smoothed out, it can be difficult to remove or re-shape if applied incorrectly.

Instead of smoothing areas out if they are higher or lower than another, vermiculite must be chopped up and refinished, making the application process longer. But, if done correctly, this shouldn’t be an issue.

Application of vermiculite takes precision since it is a lumpy material and therefore difficult to level out, particularly in areas where the pool floor meets the pool walls and where the shallow end slopes to the can be a lengthy process. However, the final product is well worth the time and effort of your pool builder.

Aside from the application and characteristics of vermiculite, it is typically the same cost or a bit more expensive product than its competition, grout.

Does a Vermiculite Pool Floor Need to be Replaced?

Just as a liner needs to be replaced, parts of a vermiculite pool floor may need to be repaired or replaced.

It is possible for the vermiculite to corrode over time, especially if tears in the liner go unnoticed. Water can seep through these tears and make its way to the pool floor. If this is a repeating issue, you may find that the pool floor has corroded when you replace the liner.

We know that this is a risk of vinyl liner pools, which is why it is so important that you keep up with the required maintenance to limit damage to any part of it, including the pool floor.

We hope that this has given you some more useful knowledge about vermiculite and how it is used for vinyl liner pool floors!

If you have any further questions, you can check out our Learning Center where we have many more articles discussing vinyl liner pools and much more!