Whether you’re building a large backyard pond, expanding an existing water garden, or installing a custom stream, you’ll sometimes need to join pieces of EPDM pond liner.
Seaming liner can feel daunting – and for good reason. Water will quickly find any mistakes you make in this process, leading to frustrating and time-consuming repairs. That’s why it’s important to do the job right the first time.
Fortunately, seaming liner correctly isn’t difficult. As long as you take your time and follow directions carefully, you can create a seam that will last as long as the liner itself.
Keep reading to learn how our team uses Seam Tape, Cover Tape and Seam Primer to create a watertight seal for years of reliable performance.
Materials You'll Need:
Scrub Pad
Rags or Scrap Underlayment
Sharp Utility Knife
Board or Other Flat Surface
Do I Really Need All That Stuff?
YES! Now is not the time to cut corners. If the seam fails, your pond will quickly lose water. The only solution at that point is to tear apart the whole feature and start again.
So let’s get to know our materials:
Liner
EPDM (Ethylene Propylene Diene Monomer) is the only type of liner that can be seamed by the average pond builder, and the only one we trust for anything that needs to hold water. This rubber-like material is flexible and fish-safe, and can last 20 years or more when installed correctly. We recommend using 45 mil (about 1.14 mm) thickness; anything less is asking for leaks.
Seam Tape & Primer
You can’t use duct tape, Gorilla tape, or other household adhesives to create a lasting bond on pond liner. You need Seam Tape and Primer. Seam Tape is a double-sided, pressure sensitive adhesive that you will sandwich between your two pieces of overlapping liner. Seam Tape isn’t like regular sticky tape. Instead, it undergoes a chemical reaction when treated with Primer, creating a permanent seal.
Cover Tape
Cover Tape is a one-sided strip of uncured EPDM with adhesive backing that protects the finished seam. It provides extra protection against movement, weathering, and mechanical stress. Because it’s made from EPDM, it stretches and ages similarly to the liner itself while shielding the seam underneath.
Surface Prep
The most important step you can take to ensure a permanent seam is to keep the liner spotlessly clean and dry. EPDM Surface Prep is a contractor-grade cleaner formulated to remove dirt, oils, and talc from new liner, while quickly tackling dirt and scale buildup on older liner. Unlike soap and water, Surface Prep dries quickly, prepping your surfaces for a long-lasting bond.
A Word of Caution
Before you start seaming, ask yourself: Is there any possible way for me to complete this project with one piece of liner?
The seaming process is not complicated, but it requires time and meticulous attention to detail to do it right. We STRONGLY recommend using a single piece of liner whenever possible.
This is especially true if you’re thinking about seaming liner in a leaky pond. You are almost always better off replacing the entire liner (which may have more holes than you realize) than you are trying to tack on a new piece of liner.
The liner is literally the thing holding your pond together. A good seam, while strong, introduces a point of potential failure. So ask yourself again: Is there any possible way to do this job with one piece of liner?
How to Seam Pond Liner: A Step-by-Step Guide
We always prefer to use a single piece of liner, but sometimes there’s just no getting around making a seam.
If you find yourself in this situation, follow the steps below to create a long-lasting, watertight seal.
Step 1: Position and Clean the Pond Liner
Lay the bottom piece of pond liner on a clean, dry surface. (A board works well). Smooth it out completely.
Next, clean the liner. The No. 1 rule to creating a successful seam is to get both pieces of liner as clean and dry as possible.
Use a damp scrub pad (like Scotch-Brite) to remove as much surface debris from the liner as possible. Even if you’re using new liner, you still need to clean to remove dust, oils, and manufacturing residue that interfere with adhesion.
Next, pour a small amount of EPDM Surface Prep on a clean, lint-free cloth. Wipe the liner thoroughly where the seam will be made, extending slightly beyond the width of the tape you’ll be applying. Use a clean section of the cloth as it becomes dirty to avoid spreading contaminants back onto the liner.
Let the Surface Prep dry completely before moving to the next step. One of the advantages of using Surface Prep is its quick flash-off, so it should dry quickly. If you’re not using Surface Prep, some people like to dry the liner with a heat gun after cleaning. (Use extreme caution if you go this route so you don’t melt the liner).
Step 2: Apply Primer to the Bottom Liner
Thoroughly shake your Seam Primer before opening. Then, using a lint-free cloth or scrap of underlayment, apply the primer evenly to the bottom piece of liner. Move in a circular motion (like Mr. Miyagi).
Allow the primer to dry until it becomes tacky but not wet. This usually takes several minutes depending on temperature and humidity. You want it to look shiny but not milky. If strands of primer come up when you poke it, it’s not dry yet.
Step 3: Attach Seam Tape to the Bottom Liner
Holding the tape paper side up, pull it about 3 inches past the area that you’ve primed. Then, slowly and evenly press down on the paper to adhere the exposed tape to the bottom piece of liner.
Seam Tape is pressure-activated. You MUST have a smooth, wrinkle-free application to create a watertight seal.
Step 4: Clean, Prime and Adhere the Top Piece of Liner
Use Surface Prep to clean the top liner. Next, position your top liner so it overlaps with the applied tape, leaving a little hanging beyond the edge. Then fold it back down to expose the tape.
Prime the top liner and allow it to dry, just like you did with the bottom piece. Remove the brown tape and press the top liner down smoothly and firmly.
Step 5: Cut Excess Top Liner Away from the Seam
Pull back the top piece of liner to where the tape starts. Then use a sharp utility knife to cut away the excess liner.
Step 6: Reinforce the Seam with Cover Tape
Next, we’re going to use Cover Tape to reinforce the seam.
Apply primer to both sides of the seam. Then center the Cover Tape, remove the backing, and press it firmly into place. The perforation down the center of the Cover Tape should align with the seam underneath.
Press and smooth the Cover Tape to remove any air bubbles or wrinkles.
Cover Tape provides an additional layer of waterproof protection while helping protect the seam from movement, weather, and long-term wear.
Tips for Creating a Leak-Free Pond Liner Seam
Following these best practices will help ensure your seam lasts for years:
- Always seam clean, dry liner.
- Work in temperatures above 40°F whenever possible.
- Always use seam primer before applying seam tape.
- Thoroughly smooth out Seam Tape and Cover Tape.
- Allow the adhesive to fully bond before putting stress on the seam.
FAQs
Can I join pond liner after my pond is already dug?
Yes. Many pond builders seam liner directly inside the excavation. Just make sure the liner is clean, dry, and supported while you work.
Is Cover Tape required?
While the Seam Tape creates the waterproof seal, Cover Tape reinforces the seam and helps protect it from long-term movement and weather exposure. You don’t want to tear apart the pond to fix a bad seam, so it’s worth the extra step.
How long does a pond liner seam last?
When installed correctly, the seam can last as long as the EPDM liner itself.
Build with Confidence
Whether you’re installing a koi pond, water garden, pondless waterfall, or stream, taking the time to properly join your EPDM pond liner will help ensure your project stays watertight for years to come.
If you need help choosing the right pond liner supplies or have questions about your project, stop by Splash Supply Company or contact our team. We’re happy to help you build with confidence.