Waterproof Membrane Thickness Selection for Pool Liners

November 07,2022

What pond liner thickness do you need? 

Intended applications and installation conditions will determine what thickness of pond liner is required. While liners may be used in fish and agricultural pools for this article we will stick with using the word pond.

Generally, thicker pond liners aka waterproof membranes are more durable, puncture resistant, and offer higher tensile strength.

Thinner pond membranes are easier to handle and install if of the same material. Although the thickness is only a difference of a few mil or millimeters, the installation and life of the pond liner will be drastically different. 

In this article, we will look at factors that will help you pick the right thickness. Prefabricated fiberglass, hard plastic ponds, and water features are outside the scope of the article however pre-formed ponds do make great options for small garden ponds.

Note: EPDM, RPE, LLDPE, HDPE, PVC, and OBC liners all have their own characteristics, features, and benefits.  

How pond liner thickness is labeled:

Waterproof membranes or plastic materials in the US are labeled in "mil". mil derives from the standard measuring system which is based on Inches. 40 mil is equal to 0.04 inches.

Things to consider:

Pond depth length and width must be considered when purchasing a liner. For example, a pond liner that is 7ft x 10ft will allow you to build a 3ft x 6ft x 1.5ft pond.

With thin liners, it's recommended to use a layer of underlayment membrane, cloth, sand, or soft dirt or gravel. Concrete is also a great option but might be a larger expense or project for most. These materials will help disperse weight and reduce the risk of puncture from rocks or roots.

Consider adding a lightweight substrate of materials (soil, gravel, rounded stones) over the pond liner to protect it from direct sunlight and puncturing


20-mil pond liner:

In most cases, small pond liners with a thickness of 20 mils will be the starting point. These products may range from 10-20 mil. Products in this category are intended for small garden ponds or light landscaping installations. Ponds using this thickness should be kept relatively shallow with a small overall footprint. 

Offering lower costs, flexibility, and ease of installation makes 20-mil pond liners budget-friendly. Thus 20-mil liners are popular for consumers undertaking small garden or landscaping projects. 

However, because these small pond liners are thin they offer low resistance to punctures and foot traffic, critter claws, or roots. UV aging from direct sunlight is also a consideration. We think starting with a 30-mil thickness pond liner is a better investment.

For larger projects with deeper depths, larger dimensions or greater water volumes should use a thicker pond liner. Areas with tree growth and rocky landscapes also require a thicker liner. 

45-60mil pond liners:

Pond liners used in commercial applications are 45 mils or thicker. RPE liners are an exception because they have higher tensile strength than other liner materials. Membranes that use EPDM start at 30 mil thickness but commercial projects use above 45 mil. The thickness gives the liners additional resistance to punctures, leaks, and seepage. Ponds using 45mil liners and above can be quite substantial.

It's still recommended to use an underlay, possibly concrete. A good example is traditional Taiwanese concrete fish farming ponds converted to use synthetic liners like EPDM, OBC, PVC, etc.  

45mil liners are heavy and don't shape and bend as well as thinner liners making them a bit more difficult to work with. These characteristics make them more expensive to ship and install.

Projects using this type of liner are generally commercial aquifers, landfills, or projects that must isolate the contents from soil or groundwater.

Overkill for hobbyists and homeowners, unless there are specific reasons to use them like rocky or areas prone to shifting. 

Above 60-mil pond liner:

Liners that fall in this category make great underlayment to thinner pond liners. The thicker liners can be placed in areas that might have heavy loads. The thicker material will disperse weight, useful if projects require heavy machinery or vehicles to traverse on them.

60 mil and above are used for chemical storage in the gas, oil, or chemical manufacturing industries.

Used when there is a need to store dangerous waste or chemicals that can impact the local environment. As 60mil and above are heavily used in commercial and industrial applications they are considered the most widely used membrane. 

For many applications, the additional thickness isn't needed and the cost can quickly escalate when purchasing thicker liners. Always consult a professional or an experienced installer that can recommend the correct pond liner thickness. 

We hope the information provided was informative, please feel free to reach out to us using the web form if you have any suggested edits, comments, or questions.

You can learn more about our pond liner and waterproofing membranes by clicking this link. 


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