Looking to install a hot tub in your backyard? A properly prepared base is essential for a stable and safe hot tub. But what type of gravel makes the best base?
For a stable and effective base for a hot tub, 3/4-inch washed clean crushed stone is a recommended choice. This type of gravel is large enough to lock together tightly when compacted, providing a solid foundation for the tub. Washed clean stone also provides excellent drainage and is self-leveling.
Contrary to popular belief, pea gravel is not a suitable choice for a hot tub base. However, it does have its uses, which will be discussed toward the end of this article.
Understanding the differences between gravel and crushed stone
There are several types of aggregate used in landscaping, which include crushed stone, gravel, sand, and fill. Each material has its own shape and size that determine its use.
When you’re looking at choices for a hot tub base, there are certain requirements that must always be adhered to in order to ensure your safety and prevent damage to the hot tub.
When laying a hot tub base made of stone, the most common choices are crushed stone or gravel. Therefore, the first thing that needs to be cleared up is the difference between the two.
What is gravel?
Gravel is a loose aggregation of stone fragments that have been formed naturally over a long period of time through the erosion and weathering of larger rocks. As water washes over the rock, it erodes, creating a smooth, shiny, and round surface.
According to the Udden-Wentworth scale, gravel can range in size from 2mm to 4mm (0.079-0.157 inches) or from 4mm to 64mm (0.157-2.5 inches). Gravel that is smaller than 2mm is considered to be sand, while larger pebbles measure above 64mm.
What is crushed stone?
Crushed rock, on the other hand, is made by machines that crush large rocks into smaller fragments. Crushing the rock creates stones that are rough and angular in shape. After being crushed, the stone is screened (“sieved”) so that it can be sorted into different sizes.
Most crushed stone is produced in quarries, and the sizes range from 10cm (4 inches) all the way down to stone dust. Screening is necessary as each construction project differs in its needs. For example, smaller stones are required for ready-mix concrete.
Although the characteristics of crushed stone make it far more suitable than gravel, there is a specific use for gravel when laying a base made from aggregate. I’ll address this later on in this article.
Get the perfect hot tub base with crushed stone
Crushed stone can provide a solid foundation for your hot tub, and it’s relatively easy to install. Here is why it makes the perfect hot base.
One of the reasons that crushed stone is ideal is because of its angular shape and rough surface, which lock together to create an immovable surface that is very strong and stable.
The fact that gravel is smooth and rounded means that it doesn’t lock together. This causes the base to shift, which compromises its support structure.
Shifting isn’t something that necessarily happens over a prolonged period of time. People have found that pea gravel has shifted out of place even during the installation process.
However, compaction is a double-edged sword. On the one hand, you need the stone to compact and lock together enough to provide stability, but on the other, you don’t want it to tamp down so much that drainage is prohibited.
One reason for choosing aggregate as a hot tub base is for its ability to provide superior drainage when compared to other materials like concrete.
Although pea gravel doesn’t compact well, its size is certainly excellent for drainage. This means we need a crushed stone that’s similar in size to pea gravel.
Measurements between 3/8” and 3/4” (mm) are ideal. This size is small enough to compact together but large enough to provide adequate drainage. However, when it comes to drainage, choosing the right type of crushed stone is as important as its size.
There are 4 types of crushed stone:
- Stone dust – Very fine dust, similar in size to sand, which is caused during the crushing process.
- Crushed stone – Crushed stone that contains a significant amount of dust in the mix.
- Clean stone – Crushed stone that has been screened to remove most of the dust.
- Washed clean stone – Crushed stone that has been screened and washed to ensure there is no dust whatsoever.
If there are any tiny dust fragments present in the mix, they will clump together and compact, restricting the flow of water. This problem is made even worse by the fact that stone dust hardens when it becomes wet.
Therefore, the most suitable type of crushed stone for a hot tub base is washed clean stone. The washing process is carried out specifically for projects that require a drainage system.
One of the most important requirements of a hot tub base is that it’s perfectly level. This is to ensure that the weight of the tub is evenly distributed.
Because gravel doesn’t lock together, it results in significant movement. Movement can occur when you get in and out of the hot tub and from the immense weight of the water circulating around the spa.
Prolonged movement can cause one side of the base to be higher than the other. It can also cause small pockets to open up between the pieces of gravel, causing the spa shell to bow. Any areas that lack support can result in cracks and other damage which are likely not covered under warranty.
To ensure proper support for your hot tub, it is recommended to have a crushed stone base that is at least 4 inches deep. This depth will provide enough gravel to lock together and form a solid foundation for the spa.
If your hot tub will be installed on a slope, you may need to add more than 4 inches of crushed stone to build up to a level surface. A crushed stone base with a minimum depth of 4 inches can support a weight similar to that of a concrete pad of the same thickness.
Wait! Pea gravel is a practical and attractive choice around your hot tub
To ensure a stable and safe base for your hot tub, it is important to measure the dimensions of the base of the tub and plan for a base that is several feet wider. This extra space will allow for spilling and splashing, which can occur when the tub is in use. You may need even more space for the side where the steps are.
One of the downsides of using crushed stone around the perimeter of your hot tub is that its jagged shape is very uncomfortable underfoot. This is where pea gravel comes in.
Pea gravel can be a great finishing touch for a crushed stone base for a hot tub. In comparison to crushed stone, pea gravel has a smoother and more rounded surface, which makes it more comfortable to walk on and less prone to causing accidents.
Pea gravel also comes in a wide range of colors, which allows for more creativity and flexibility in landscaping design. Using pea gravel as a border around a hot tub base can add a visually appealing and practical touch to the area.
Just ensure that the gravel isn’t so small that it sticks to the soles of your feet. Choose pea gravel that measures 10mm (3/8″).
Note: When planning for your base, don’t forget to also allow enough clearance space for your cover, cover lifter, and access to the internals.