By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. View our Privacy Policy for more information.
Blog Article

Sustainable bunker care: Why you should never add more sand to your bunker base to dry it out

Editorial Team
Sustainable bunker care: Why you should never add more sand to your bunker base to dry it out
December 8, 2023

Stockholms GK, Sweden

One of the significant challenges faced by golf courses is maintaining the ideal moisture level in bunker sand. Excessive moisture can lead to waterlogged conditions and algae growth, negatively impacting the bunker's appearance and playability.

This issue can appear more severe if there is a capillary breach below the sand, as is the case with most golf course bunker liners. Modern bunker sands also contain more of the fine silt and clay particles (below 0,2 mm), which is a result of the popular crushing method used to produce angular bunker sands. The USGA does not publish an official specification on golf bunker sands, but recommends a maximum of 3% of silt and clay particles (below 0,05 mm) in bunker sand.

USGAs particle size guidelines for bunker sand

The problem with this recommendation is that there is a significant difference between the particles within this gradation, where the particles below 0,02 mm or the very fine silt and clay are much more prone to migration. Rain and irrigation move these particles down over time, and finally the sand at the bottom of the bunker has so many of these fine particles that it stays too wet almost all the time.

A common solution deployed to address this problem has been to increase the sand depth in the base of the bunker well above the USGA recommended 4 inches. However, this approach is costly and provides only a short-term fix. In fact, it merely covers up the underlying issue that is likely to resurface within a year or two. The real problem lies in the fines (particles below 0,2 mm) accumulated within the sand, not the sand itself.

In this blog, we will talk about what causes the wetness in bunker bases and how CapillaryFlow’s new Capillary Wash Box technology can easily fix it.

The Capillary Wash Box

Bunker sand moisture levels

What determines the amount of moisture in sand in a golf course bunker? Presuming the grass around the bunker is alive, this depends on three things:

1. How deep is the sand?

2. How compacted is the sand?

3. What is the gradation of the sand, or how many fine particles does the sand contain?

So far, golf course superintendents have managed factors 1 and 2 with golf bunker maintenance programs such as raking, re-positioning and compacting. They often address factor 3 by adding more sand to the base of wet or dirty bunkers or opting for an expensive complete sand replacement.

But this is an expensive and time-consuming way to solve a problem that could easily be fixed with the correct method. 

Golf bunker sands will change over time, and keep changing due to the constant contamination and migration of fines and organic matter. Golf bunkers are also placed in very different microclimates on the same course. One south-facing fairway bunker will have very dry conditions compared to a green-side north facing pot-bunker. The key here is that the maintenance team needs to adjust the amount of fine particles in bunkers to the location, steepness of faces, and shape of the bunkers.

The key to a dry bunker floor therefore lies not in the quantity of sand but depends on two important factors:

1. Overall golf course drainage: There must be a well-designed drainage system on the golf course. Both surface drainage and pipe systems must be correctly built and designed to divert water to suitable locations, and the bunkers must be a part of this system. If the pipe does not remove the water quickly, the bunker will stay wet no matter what the sand does.

2. The regular removal of fines and organic matter: There is no way around this in the future. Top level golf course maintenance will involve regular adjustment of fine particles and organics in bunker sands. Apart from being significantly more sustainable as a practice, this also ensures the correct compaction of the bunker sand afterwards instead of the 2-4 week period of plugged ball lie, loose sand conditions of a new sand. To add new bunker sand to bunkers merely to create dryer floors and cleaner sand is totally unsustainable and golf courses should abandon them just like mercury pesticides.

The good news is that today, systems and tools for maintaining golf bunker sands have taken significant technological leaps. More precise, economical, and sustainable methods to reduce moisture in the bunker base are available, achieved by adjusting the amounts of fine particles and organic contaminants.

Introducing the solution: Capillary Bunker liners and Capillary Wash Box

Capillary Bunkers, in conjunction with the Capillary Wash Box, is the optimal bunker liner solution for golf courses. The combined solution not only provides golf courses with the unique capability to wash bunker sand, eliminating the need for costly sand replacement, but also allows golf courses to maintain a correct sand depth in bunker floors so that the bunker plays and performs as intended.

By efficiently removing fines from bunker sand, the Wash Box significantly enhances the overall performance of the bunkers. This reduces the occurrence of wet bunker floors, ensuring a consistent high level of playability over the course of years.

No other bunker liner, whether comprising fabric or porous aggregates, allows you to wash bunker sand. Capillary Bunkers and Capillary Wash Box are the only options that enable this process.

Overview of the Capillary Bunkers system, with the Bunker Liner, Edge and Wash Box

How Capillary Bunker liner and Wash Box work

The Capillary Bunker liner comprises Capillary Material, a patented pervious cement ­and polymer material – the only building material capable of rapidly draining water while also moving it upwards. The solution enables golf course superintendents to effectively control moisture across the entire bunker surface, a crucial factor for optimal bunker performance. When sand dries out on steep bunker faces, the risk of plugged ball lies and washouts increases, and soggy bunker bases affect playability. The Capillary Bunker liner swiftly drains excess rainwater while redistributing moisture to bunker sand during dry weather, retaining optimal moisture levels. This not only prevents washouts but also ensures impeccable playing conditions in any weather and terrain.

Additionally, the Capillary Wash Box enables golf courses to regularly wash the bunker sand, removing accumulated contaminants like algae, debris, silt, clay, and organic pollutants. This preserves the sand’s percolation rate, color, and desired playing properties, eliminating the need for frequent sand replacement.

Washing the sand with the Wash Box

The ability to rapidly drain excess water, move moisture up to the sand in dry weather, and wash the sand is one major reason why Capillary Bunkers and Wash Box represent a huge improvement over conventional bunker liners for golf courses. Furthermore, unlike other golf bunker liners, Capillary Material retains its strength over time.

Thousands of bunkers around the world, including many of golf’s top 100 courses, have successfully been renovated with Capillary Bunkers and Wash Box. On top of drastically improving the playability of bunkers, customers experience significant maintenance savings and +35% ROIs.

At CapillaryFlow, we're so confident in our technology that we offer an industry-leading 15-year structural and drainage performance guarantee on our complete Capillary Bunker system and equestrian sand footing solution, including liner, vaults, and wash boxes.


To conclude, do not ever add more sand in the base of bunkers to make them dry out! We cannot emphasize this enough.

Instead, use a Capillary Wash Box and water to effectively eliminate fine particles and organic contaminants from bunker sand. This will immediately dry up the sand to your exact desired level. 

In essence, if your bunker sand adheres to USGA recommendations, you should never have to exceed 4 inches (10 cm) on the bunker floor and always maintain less on the faces.

This is a big deal. This is real sustainability.


Want to know more about our products?

Would you like to know more about how our Golf Course and Bunker Renovation Services work? Or how Capillary Bunker liners can help you build bunkers with durable edges, consistent playability, washable sand, optimal drainage and significantly less maintenance? Contact us!


CapillaryFlow makes it possible to design baseball fields that are able to withstand tough playing conditions as well as ensure a healthy game experience for players.

Capillary Bunkers

Our proprietary Capillary Material makes it possible to have a bunker liner that rapidly drain while also retaining adequate sand moisture, creating the perfect playing conditions in golf course bunkers.

Capillary Edge

Use a durable bunker edge that molds and bends to any shape to ensure exact original bunker shapes throughout your bunkers’ lifetime, with no soil that ever escapes into the bunker sand

Geothermal heating icon

Capillary Geothermal

Capillary Geothermal distributes an even heat regardless of ground profile and let grass grow and sports be played for longer throughout the season.

Capillary Hydroponics grass icon

Capillary Hydroponics

The Capillary Hydroponics system enables us to grow strong and durable grass with significantly less maintenance and environmental impact


Optimal riding conditions in any weather by providing a ground material technology  offering superior drainage capacity and enabling use of subsurface moisture control - for the optimal footing


Capillary Hydroponic turf lengthens the season with natural strong grass that stays healthier even with a busy schedule


From pristine golf bunkers to precisely trimmed golf greens, our proprietary solutions make it possible to build and maintain some of the most beautiful golf courses in the world.

Green Cities

Our Capillary Hydroponics solution turns hardscaped surfaces into breathable, living spaces that augment the positive effects of greenery in urban environments.

Subscribe to our newsletter