Hi all, Looking for some thoughts on base and backfill materials, specifically for a fiberglass installation. I have done lots of research and spoken with many experts (local and online) on the benefits and challenges of sand, gravel, round stone or pea stone, and even flowable fill.
Sand - seems to be the old standard, and while soft, and easy to grade for a base, it allows for settling and even wall bulging (especially when wet). I know many people talk about being able to 'wash' the sand into voids, but my research also indicates that this is not as effective as many installers and manufacturers will lead you to believe. I'm inclined to think that this may still be one of the best materials for base material (so long as water does not get under the pool shell and the base was prepared perfectly).
Gravel - 3/4" minus washed stone seems to be very solid, allows for water to pass through, naturally compacts when placed (upwards of 90%, I believe), and does not have the same challenges as sand. That said, even though the pieces are small and should not cause damage to a fiberglass shell, and some reputable installers will swear that there is not chance for damage, they are still angular and sharp in nature, causing potential for damage.
Round Pea Stone - My understanding is that this has many of the benefits of gravel, but without the sharp edges, thereby removing the potentially hazzardous sharp edges. Supporters will say that makes this a better medium than gravel, but others have said the stone's round nature act like ball bearings against each other and cause slippage and settling.
Flowable fill - I'm still learning of the properties of this material, however, it sounds as though it's extremely sturdy and easier to fill into difficult areas (without leaving voids or falling back), such as under stairs and swimouts. I know that most FG manufacturers reinforce these areas of their shells, but also that these areas are difficult to back fill and are prone to cracks if not backfilled properly.
Based on the below info, wondering if the best approach is a sand base with round peastone side fill and flowable fill underneath stairs and swimouts. Thoughts? Thanks.