Key Takeaways

• Bunker liners are typically installed to reduce washouts and/or sand contamination.
  
  
• Every liner option has advantages and disadvantages.
  
  
• Porous aggregate liners are a popular choice, but they cost more than other options and can create a perched water table in bunker sand that causes it to hold more moisture than desired.
  
  
• Other options may not be as durable as porous aggregate liners, or as effective for reducing washouts, but they typically cost less and won’t cause the sand to retain excess moisture.
  
  
• Even with a liner, it is still important to direct surface water away from bunkers and to implement maintenance practices that limit contamination.
  
  

This is an updated version of an article written by George Waters and former USGA agronomist Todd Lowe that was published in the October 5, 2018, issue of the USGA Green Section Record. This version contains new insights and current pricing estimates. Updated bunker liner cost ranges were derived with assistance from the Golf Course Builders Association of America and individual golf course construction and project management firms that work across the U.S.

Reducing Contamination

Reducing the contamination of bunker sand is another reason to install a liner. Creating a barrier between the bunker sand and subsoil prevents the upward migration of fine particles and stones into the sand, extending its useful life. A liner also prevents contamination of bunker sand with soil from the bunker floor during washouts and washout repair. If a bunker does not have a liner, washouts will erode the subsoil and contaminate the bunker sand.

Liners cannot prevent all types of bunker sand contamination, however. Some liners cannot be extended up the vertical edges of bunkers, leaving open the possibility of contamination from bunker edge erosion. Some courses have used one type of liner for the bunker floor and another to cover the edges as a way to address this issue. A liner also cannot prevent contamination that comes from outside the bunker. Examples include soil carried by surface water and airborne debris such as tree litter, grass clippings and dust. If external contaminants are a potential issue, additional management strategies will be needed to ensure the desired bunker performance.

Improving Playability

Bunker liners can improve playability in several ways. By reducing washouts, liners decrease the amount of time that bunkers are disrupted after a rain event. Fewer washouts also mean less issues with soft sand in recently repaired areas. Unless repositioned sand is carefully compacted during washout repair, buried lies can be problematic.

Liners can also help maintain the performance and consistency of bunker sand. Without a liner, subsoil contamination can slow drainage through bunker sand, eventually causing areas of a bunker to play more firmly or to hold water. A liner also prevents stones and pebbles from migrating into bunker sand and creating playability and maintenance issues in the bunker and on the surrounding turf. This is especially important for greenside bunkers because any stones or pebbles splashed from the sand onto a green can disrupt putting and damage mowers.

Some liners also improve moisture consistency in bunker sand. However, it is important to recognize that more-consistent sand moisture may not necessarily translate into the desired playability. There are many other factors involved in how sand plays and how its performance is perceived by golfers.

Are There Situations Where a Liner Is Not Necessary?

Bunkers that have gently sloped or flat sand, with surface water effectively directed around them, will not typically experience significant washouts. The sand in these bunkers will also have relatively consistent moisture – barring external factors like sprinklers that only hit certain parts of bunkers – because there is limited elevation change in the sand. If contamination is not a serious concern, there may be no reason to install liners in bunkers of this nature.

Potential contamination from stones or soil may not necessarily require a liner to be installed. Bunkers that experience some form of contamination can still provide adequate playability. In fact, some of the most famous golf courses in the world have small stones scattered throughout their bunkers. The size of the stones and their prevalence are key factors to consider. Contamination from native soil will decrease bunker sand performance over time, but the cost of installing a liner to prevent this issue should account for golfer expectations and be balanced against the cost of periodically replacing the sand.

Bunkers situated on extremely sandy soils are also unlikely to require liners, although some sandy soils do contain stones or fine particles that may make a liner desirable.

Liner Types

There are many different liner options to choose from and each has its advantages and drawbacks. Selecting the appropriate liner for your project requires balancing cost with performance goals and understanding golfer preferences at the facility. Researching the performance of liners in your area and testing various options on your site with your desired bunker sand is critical for achieving a satisfactory outcome.

Porous Aggregate Liners

Cost Range ($3.25-$6.50 per square foot, materials plus installation)

Advantages

Porous aggregate liners such as gravel with a stabilizing polymer and porous concrete are commonly used in bunkers today. These materials provide drainage throughout the bunker and have a texture that helps to hold sand on bunker faces. They are typically installed in a layer that is several inches deep, effectively eliminating contamination from the subsoil. Porous aggregate materials are more durable than most other liner options and hold up well to daily maintenance practices. They do not require any staples or fasteners, which eliminates a potential maintenance issue. These liners are typically installed by a contractor, and some products require a certified contractor.

Limitations

Porous aggregate liners are more expensive per square foot than many other options and require extra excavation during the bunker shaping process to account for the thickness of the liner. They also often require increased sand depth to improve surface dryness by exceeding the typical perched water table height – commonly 6-7 inches of sand or more – which increases total project cost. Porous aggregate liners cannot be formed up the vertical edge of a bunker, so sand contamination from the bunker edge is still possible if an artificial material isn’t used to create a seal around the bunker edge. Maintaining adequate sand depths is important with these liners to prevent golfers from striking a hard surface during a shot or having balls bounce off exposed liner.

Installing a layer of porous aggregate beneath bunker sand carries the risk of creating a perched water table that may cause the sand to remain wetter than desired. This issue is a particular concern in humid regions with more rainfall or on areas of a golf course that receive frequent irrigation. Wet sand creates firm playing conditions and may allow algae to become established, which can be both an aesthetic and playability issue.

Porous aggregate bunker liners also have specific requirements for their composition and installation. This may limit the availability of some products, restrict who can install them and influence installation timing. Products that require a spray-on polymer typically have moisture and temperature restrictions and it may not be possible to obtain or install concrete-based products below a certain temperature. Most porous aggregate liners also require a certain amount of time to cure before they are ready for sand. If the installation and curing process are not performed correctly, there is a risk that pieces of aggregate can come loose from the liner and contaminate the sand. The process of transporting large amounts of porous aggregate material throughout a golf course to install in bunkers can also be disruptive.

Tips for Success

It is essential to test the compatibility of porous aggregate liners and bunker sands. Both a bridging test and a water release curve test should be performed by an accredited lab prior to construction. The water release curve determines how many inches of sand will be required to avoid excessive moisture retention. If testing reveals that the required sand depth is greater than desired, a more affordable solution may be to create openings in the liner that allow water to flow freely into the bunker drainage system. Some courses have also created exaggerated low areas in the liner to allow for deeper sand and faster drainage, or some have created U-shaped grooves in the liner and laid the drainage lines above the liner itself to create free drainage. It is important to coordinate with the manufacturer when planning any modifications to the specified liner design and installation protocol so that you are fully aware of any performance or warranty implications. The moisture content of porous concrete products must be carefully monitored for the desired consistency. A simple test is to squeeze some of the product in your hand – the mix should stick and have a moist appearance without being runny.  

Fabric Liners

Cost Range ($2.00-$4.00 per square foot, materials plus installation)

Advantages

Fabric bunker liners have been in use on golf courses for decades. Their principle advantages are low cost in comparison to other liners, easy installation, reduced sand contamination and effective washout control. On steep bunker faces, white fabric liners can also create the illusion of adequate sand even if the liner itself and a small amount of sand are the only things present. Because fabric liners are flexible, the liner itself is also resistant to damage from frost heave.

Limitations

The limitations of fabric liners are well known. Pieces of the liner can be dislodged or torn and brought to the surface by mechanical bunker rakes or animals digging in the sand. Sections of liner can also come to the surface when the staples or nails holding the liner to the subgrade are lifted by freeze-and-thaw cycles or have corroded over time. Staples coming to the surface after being dislodged from the subsoil is another issue.

Once a section of fabric liner has come to the surface, the only way to properly address the problem is to pull back the surrounding sand, ensure that no sand is underneath the liner, and then reaffix the liner to the subgrade. If the liner is torn or damaged it may be necessary to install a patch. Unfortunately, when fabric liners come to the surface of a bunker the misguided solution is often to cut or tear the exposed piece and then cover the damaged area with sand. This compromises the integrity of the liner and is only a temporary solution. Sand will soon migrate beneath the liner in the torn area and eventually more liner will come to the surface.

Tips for Success

There are several approaches to managing the issue of fabric liners coming to the surface. It is commonly recommended to avoid using a mechanical bunker rake if fabric liners have been installed. However, choosing a low-cost liner that necessitates high-cost hand raking does not make much sense for many facilities. Mechanical rakes can still be used in bunkers with fabric liners, it simply becomes essential to maintain adequate sand depths to ensure that the rake does not snag the liner. Rake attachments will also need to be less aggressive to avoid digging deeply into the sand and catching the liner.

Follow manufacturer recommendations for the type of fasteners and proper spacing. When in doubt, more staples will not add much cost but may improve performance. Applying an industrial-strength adhesive along the seams of the liner and over top of the installed staples can help consolidate the liner and reduce the risk of failure in weak areas, although using adhesives is not guaranteed to prevent frost heave from lifting the staples.

Synthetic Turf Liners

Price Range ($3.75-$6.50 per square foot, materials plus installation)

Advantages

Synthetic turf liners provide many of the same benefits as traditional fabric liners, without some of the limitations. They are heavier and more durable than traditional fabric liners, making them less vulnerable to damage from mechanical rakes or animals. Synthetic turf liners reduce washouts and eliminate sand contamination from the subsoil. These liners also typically include a component that can be placed over the bunker edge, eliminating another potential source of sand contamination. Synthetic turf is flexible, making it resistant to damage from freeze-and-thaw cycles. It can also be installed in-house or by a contractor during a wide range of weather conditions. Synthetic turf liners are soft, which reduces any risks associated with the liner being struck during a bunker shot. They also will not create a perched water table in the sand.

Limitations

The weight of synthetic turf liners makes installation more challenging than traditional fabric liners. They also typically come in a multipart system with different components for the bunker floor, edges and around the drainage lines, adding complexity to the installation process. Bunkers that feature complex shapes and edges will lead to more waste as these products are cut to fit.

Tips for Success

Installing synthetic turf liners so that the grain of the fabric points up the bunker slope will help reduce washouts. Some facilities have also had success lining only bunker faces with synthetic turf liners. With these “hybrid” installations, the bunker floors are either left unlined or are lined with a less costly and/or more permeable material.  

Sod Liners

Cost Range ($0.50-$2.00 per square foot, materials plus installation)

Advantages

Lining bunkers with sod can be an effective, low-cost solution to limit contamination issues. The thatch and roots from the sod create a barrier that prevents stones and native soil from contaminating the bunker sand. Sod liners can also be joined with the surrounding sod to reduce contamination from bunker edges, and sod liners are resistant to damage from frost heave.

Limitations

The lifespan of sod as a bunker liner is unclear. Facilities have reported more than 10 years of effective performance, but that number could be higher or lower depending on local conditions. While the lifespan of sod liners may be shorter than other liner options, the cost of replacing sod liners is low. In most cases, sod liners could be entirely replaced several times before approaching the cost of installing a porous aggregate liner, but that would involve more disruption.

Sod liners will not provide enhanced drainage, nor will they provide much benefit in limiting washouts. Therefore, they are primarily an option for bunkers with gently sloped faces and effective control of surrounding surface water. In areas where animals digging in bunkers is an issue, sod liners may not be a good option. Mechanical bunker rakes can be used in bunkers with sod liners, but the same precautions should be taken as with fabric liners.

Tips for Success

The most important factor in achieving good performance from sod liners is allowing sufficient time for the turf to root into the soil before installing bunker sand. Typically, three to six weeks is recommended for establishment. When selecting sod for bunker liners, be aware that some turf species are more likely to grow through the sand than others. It might be sufficient to scalp and bury ryegrass, but Kentucky bluegrass and warm-season grasses should be sprayed with a nonselective herbicide prior to sand installation. If in doubt, applying a nonselective herbicide is an inexpensive way to make sure that grass from the liner does not grow through the sand. It is important to select sod for the liner that has either no mesh or a biodegradable mesh that will break down over time. Nonbiodegradable mesh can find its way to the sand surface over time and cause maintenance issues. Sod that has a higher thatch content would be preferred as a bunker liner because that organic material and root mass is what creates the barrier between sand and the subsoil.

Other Liner Types

Impermeable Liners

There is a broad range of impermeable liner options, including spray-on products and aggregates that can be compacted into an impermeable layer. Impermeable liners tend to be long-lasting and they are effective at eliminating contamination from the subgrade. They typically have a texture that helps sand adhere to slopes and they are relatively resistant to damage from mechanical bunker rakes. Some impermeable liners are potentially vulnerable to damage from frost heave because they are rigid.

Porous Rubber

There are several versions of porous rubber liners, some are mixed with a binding agent and spread while others come in rolls and are cut to size and stapled to the bunker floor or connected together with adhesive and not stapled. Porous rubber products are more durable than fabric liners and provide enhanced drainage. They are also flexible, making them resistant to damage from freeze-and-thaw cycles. The installation of rolled products is similar to any fabric liner, although the material is heavier and therefore more challenging to work with. Products that are mixed with a binding agent can be more difficult to install because they must be mixed on site and carefully spread over the bunker floor. There is also a risk that improper installation or damage during maintenance can cause pieces of the liner to flake off and contaminate the sand over time.

Conclusion

Making decisions about bunker liners is not easy. There is limited objective research on the topic and there are many factors involved in making the best decision for your course. Testing different liner options in a few demonstration bunkers prior to beginning a large-scale bunker project is strongly recommended. Liners will perform differently based on bunker design, the sand chosen, the maintenance program and the local environment. It is invaluable to allow golfers and decision-makers the opportunity to experience the playing conditions and observe how different liners perform prior to making a significant investment.

It is also important to recognize that bunker liners will not cure all issues on their own. Surface water management, subsurface drainage, sand selection, architectural style and maintenance practices in and around bunkers all play a role in the issues that many liners are selected to address. Making adjustments in these areas to protect bunkers from contamination and reduce the risk of washouts will help you get the most benefit from the liner you choose, and may allow you to select a lower-cost option while still achieving the desired results.